Re: Class 1 AC/DC adapter
Rich, Rich Nute ri...@sdd.hp.com Sent by: owner-emc-p...@majordomo.ieee.org 07/11/03 06:57 AM Please respond to Rich Nute ri...@sdd.hp.com To peter.tar...@sanmina-sci.com cc emc-p...@ieee.org Subject Re: Class 1 AC/DC adapter Hi Peter and Raymond: To verify the veracity of my memory, I went to my lab and took two manufacturer's C14 appliance inlets and applied 5kVac from both poles to the earthing terminal for 7 mins. each, with the instrument sensitivity adjusted to its maximum (eg, minimum current flow tripping the indicating circuit). Both showed no signs of breakdown, except for a misapplied lead on one of the EUTs (which was corrected as soon as DB was noted as the test potential approached 4.8kV; reapplying the leads more carefully and retesting proved very successful). No typographical error: 5kVac for 7 mins. The C14 inlet has 5 mm between mains and PE. This is a constructional requirement based on the location of the pins relative to each other. As a stand-alone, and having something better than a purely inhomegeneous field, the C14 inlet should readily withstand 5 kV -- forever. However, when wires are attached to the terminals, the clearances are necessarily reduced. Likewise, when the appliance inlet is soldered to a PWB, the traces on the PWB will reduce the spacings to less than 4 mm, and we can expect breakdown in the neighborhood of 5 kV. You are quite right that is the case applied to our ps. Best regards, Rich Thanks and regards, Raymond Li OSA This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Class 1 AC/DC adapter
Hi Peter: The body shape and dimensions, the pin sizes shapes, dimensions and orientations where they interface with an appliance coupler I know are defined. I don't have copies of all of the IEC60320 documents and am unaware that the product interior side of the appliance inlet is defined in those standards. The IEC 60320 does not specify the interior side of the inlet. However, IEC 60320 does specify a minimum spacing of 4 mm between mains and the PE anywhere on the inlet. In the best case, the interior would also meet the same spacings, 5 mm, as the mating face. Some manufacturers include a ridge between all terminals so as to guarantee the spacing is at least 5 mm. Do these standards also control the form-factors so that that one SMD has the same foot print as another? Same for through-hole devices? How the conductors are routed and the other shapes not addressed by a standard could conceivable contribute to DB at a finite potential greater than 2kVac specified in IEC60320-1. No, the form factor and foot print are not specified in IEC 60320. The distance and the conductor shape determine the electric strength of any pair of conductors or conductive parts. The greater the distance, the greater the electric strength. The more homogenous the electric field (created by the shape of the conductors), the greater the electric strength. Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Class 1 AC/DC adapter
Rich - The body shape and dimensions, the pin sizes shapes, dimensions and orientations where they interface with an appliance coupler I know are defined. I don't have copies of all of the IEC60320 documents and am unaware that the product interior side of the appliance inlet is defined in those standards. Do these standards also control the form-factors so that that one SMD has the same foot print as another? Same for through-hole devices? How the conductors are routed and the other shapes not addressed by a standard could conceivable contribute to DB at a finite potential greater than 2kVac specified in IEC60320-1. Regards, Peter L. Tarver, PE ptar...@ieee.org From: Rich Nute Sent: Thursday, November 06, 2003 3:07 PM Hi Peter and Raymond: Raymond doesn't have to do this. The dimensions of the standard C14 specify 5 mm between mains and PE. The dimensions of the pins determine the field shape. These two sets of dimensions set the withstand/breakdown of the C14. Therefore, each and every C14 will withstand 5 kV. The breakdown in Raymond's unit is not the C14 itself, but probably on the back of the main PWB, either where the C14 is soldered to the board or where the Y-caps are soldered to the board. This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Class 1 AC/DC adapter
Hi Peter and Raymond: To verify the veracity of my memory, I went to my lab and took two manufacturer's C14 appliance inlets and applied 5kVac from both poles to the earthing terminal for 7 mins. each, with the instrument sensitivity adjusted to its maximum (eg, minimum current flow tripping the indicating circuit). Both showed no signs of breakdown, except for a misapplied lead on one of the EUTs (which was corrected as soon as DB was noted as the test potential approached 4.8kV; reapplying the leads more carefully and retesting proved very successful). No typographical error: 5kVac for 7 mins. The C14 inlet has 5 mm between mains and PE. This is a constructional requirement based on the location of the pins relative to each other. As a stand-alone, and having something better than a purely inhomegeneous field, the C14 inlet should readily withstand 5 kV -- forever. However, when wires are attached to the terminals, the clearances are necessarily reduced. Likewise, when the appliance inlet is soldered to a PWB, the traces on the PWB will reduce the spacings to less than 4 mm, and we can expect breakdown in the neighborhood of 5 kV. Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Class 1 AC/DC adapter
Hi Peter and Raymond: In the sake of fairness, it should be noted that both of my EUTs had solder loops and were not intended for surface or through-hole mounting to a PWB. For the sake of our mutual edification, it would be interesting to see how the appliance inlet in Raymond's customer's power supply might perform, desoldered from the board and tested to determine its ultimate breakdown potential outside the power supply. This would be a good exercise for Raymond to also provide his customer with the best possible advice. Raymond doesn't have to do this. The dimensions of the standard C14 specify 5 mm between mains and PE. The dimensions of the pins determine the field shape. These two sets of dimensions set the withstand/breakdown of the C14. Therefore, each and every C14 will withstand 5 kV. The breakdown in Raymond's unit is not the C14 itself, but probably on the back of the main PWB, either where the C14 is soldered to the board or where the Y-caps are soldered to the board. Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Class 1 AC/DC adapter
Raymond - Please see the below. Regards, Peter L. Tarver, PE ptar...@ieee.org From: Raymond Li Sent: Thursday, November 06, 2003 9:18 AM Peter, I am pleased to give you greater details below as required. What we don't know (or I've lost track of): DK2) what mains connected part(s) are involved in the dielectric breaking down (transformer winding terminations, leads or bodies of filtering, surge suppression or other components and how they are mounted) According to Rich's suggestion, the PCB mounted AC receptacle contributes the breakdown. From the signs of breakdown, there were two places of breakdown between the mains copper tracks and earth copper track of the receptacle where have less than 5 mm spacing. Also per Rich Nute's other posts, it was stated that the electrical spacings in IEC60950 are conservative, inferring breakdown might not occur, even at significantly smaller creepages for the same applied potential. I agree with this statement and must suggest that the spacings must be much closer to 2.5mm (for Basic Insulation, up to 250Vac) than your earlier e-mails led me to believe. This is no doubt a problem with my interpretation of your problem statement. DK4) if the supply uses an appliance inlet, has a nondetachable power supply cord or if it a direct plug-in type and how the mains circuit is brought to the power conversion element(s) of the primary circuit The power is brought in via a detachable power cordset. As explained by Rich, the class 1 AC receptacle is designed for the hi-pot of 1,500 Vac. It cannot withstand 3,000 Vac together with associated pcb tracks. Probably why the designer has to design it in that way. Such design gives challenge at final stage testing in production and incoming QC. I think you may have misread or misinterpreted Rich's statement. Rich did not state the receptacle was at the probable root of the breakdown, but rather related to Basic Insulation used in Class I Equipment for which this style appliance inlet is used. I know from direct experience that an IEC320 C14 appliance inlet (assuming this is what's used) can withstand 3000Vac from both poles to ground. If the problem location is at the appliance inlet, it must be due to the particular implementation of the inlet, or at the board it's mounted to. To verify the veracity of my memory, I went to my lab and took two manufacturer's C14 appliance inlets and applied 5kVac from both poles to the earthing terminal for 7 mins. each, with the instrument sensitivity adjusted to its maximum (eg, minimum current flow tripping the indicating circuit). Both showed no signs of breakdown, except for a misapplied lead on one of the EUTs (which was corrected as soon as DB was noted as the test potential approached 4.8kV; reapplying the leads more carefully and retesting proved very successful). No typographical error: 5kVac for 7 mins. I note that IEC60320-1, §15.3, only requires 2kVac from both poles to the earthing terminal. This suggests to me that, if the appliance inlet was responsible for the DB, the implementation of the C14 design would have to be responsible. In the sake of fairness, it should be noted that both of my EUTs had solder loops and were not intended for surface or through-hole mounting to a PWB. For the sake of our mutual edification, it would be interesting to see how the appliance inlet in Raymond's customer's power supply might perform, desoldered from the board and tested to determine its ultimate breakdown potential outside the power supply. This would be a good exercise for Raymond to also provide his customer with the best possible advice. If you do this, Raymond, I'm certain the group would appreciate knowing the test results. Regards, Peter L. Tarver, PE ptar...@ieee.org This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Class 1 AC/DC adapter
Dear Guys, Many thanks for who responded to my queries. The information and suggestion given are very useful and informative. At the end of day, the ps is subjected to 1,500 Vac hi-pot test and, as a compromise, a 10A earth continuity test as suggested in routine tests of EN 60065. Raymond Li OSA ChengWee Lai c...@netscreen.com 06/11/03 08:54 AM To 'peter.tar...@sanmina-sci.com' peter.tar...@sanmina-sci.com, emc-p...@ieee.org cc raymond...@omnisourceasia.com.hk, ChengWee Lai c...@netscreen.com, 'Rich Nute' ri...@sdd.hp.com Subject RE: Class 1 AC/DC adapter Hello Guys, Apologies for getting into many IF's. Yes, our discussion is based on assumption and description provided. There are many unknown for us on his unit. I believe the fundamental of the safety concept, which have been discussed should be look in depth by Raymond. Maybe it is time for Raymond to give us some input over the different area we discussed. Best Regards, Chengwee From: Peter L. Tarver [mailto:peter.tar...@sanmina-sci.com] Sent: Wednesday, November 05, 2003 7:40 AM To: emc-p...@ieee.org Cc: raymond...@omnisourceasia.com.hk; c...@netscreen.com; 'Rich Nute' Subject: RE: Class 1 AC/DC adapter Let's look at these what ifs. From: ChengWee Lai Sent: Tuesday, November 04, 2003 4:38 PM Raymond might be able to convince Safety agency to accept PE continuity test with 1500Vac Hipot at the production line. However in the Scenerio with end customer, it could mean business or no business. Question regarding: Whether customer can accept his adaptor with only 1500Vac hipot tested where other power supplies can withstand 3000Vac? The only clear answer is some form of redesign is necessary. Simple solutions work best. For any reasoned advice, there are too many unknowns about the physical construction of the power supply. See the below for more on this. Would that affect his customer Safety testing, because his customer unit with his power supply only meet 1500Vac hipot after heating test? Only Raymond and his customers can answer this. Or what if Safety agency require his customer unit to do grounding test to accessible metal part? OK, but why? The discussions have centered around an SELV output, making the end product Class III. There would have to be some specific about the final application to justify this. We have no information to base such an assumption on. Regards, Chengwee As with many discussions on the list, practical issue discussions often get side tracked by the hypothetical and theoretical. More to the point, Raymond hasn't given us specifics on the physical orientation of parts in the power supply to any great degree. Proprietary information aside, we know: K1) the insulation between earthed parts and mains connected parts is somewhat better than Basic, but not Reinforced K2) the EST potential where breakdown occurs (though I've discarded the e-mail with the identified potential) K3) the breakdown is suspected (or possibly confirmed) to occur to the earthed board that is used as an EMC shield and which also electrically connects to an SELV output What we don't know (or I've lost track of): DK1) if the power supply is a linear or switched mode type (we can assume it's a SMPS, since EMC shielding was mentioned, but it would be nice to have confirmation) DK2) what mains connected part(s) are involved in the dielectric breaking down (transformer winding terminations, leads or bodies of filtering, surge suppression or other components and how they are mounted) DK3) what area or specific portion of the earthed parts are involved in breaking down (at solder connection points for lead wires, the copper on the shielding board) DK4) if the supply uses an appliance inlet, has a nondetachable power supply cord or if it a direct plug-in type and how the mains circuit is brought to the power conversion element(s) of the primary circuit With some of this additional information, a more practical solution may be possible, rather than talking around the specifics. A WAG or two: One issue that hasn't come up is whether or not the copper on the shielding board is facing the mains/primary circuitry or not. Based on the application and the general discussion, this board appears to be separate and independent of the mains/primary circuit board. If this is true, it seems logical that the board is single-sided. If the board is single-sided and the copper is facing the mains/primary circuit, has anyone considered flipping the board over and relying on the base laminate to provide Supplementary insulation to a clearance? If the first WAG is unusable, why not add a 0.4mm thick insulating sheet between the earthed board and the portion of the primary circuit involved in breaking down? This will effect margins and pricing, but sometimes one must
RE: Class 1 AC/DC adapter
Peter, I am pleased to give you greater details below as required. Peter L. Tarver peter.tar...@sanmina-sci.com 05/11/03 11:40 PM Please respond to peter.tar...@sanmina-sci.com To emc-p...@ieee.org cc raymond...@omnisourceasia.com.hk, c...@netscreen.com, 'Rich Nute' ri...@sdd.hp.com Subject RE: Class 1 AC/DC adapter Let's look at these what ifs. From: ChengWee Lai Sent: Tuesday, November 04, 2003 4:38 PM Raymond might be able to convince Safety agency to accept PE continuity test with 1500Vac Hipot at the production line. However in the Scenerio with end customer, it could mean business or no business. Question regarding: Whether customer can accept his adaptor with only 1500Vac hipot tested where other power supplies can withstand 3000Vac? The only clear answer is some form of redesign is necessary. Simple solutions work best. For any reasoned advice, there are too many unknowns about the physical construction of the power supply. See the below for more on this. Would that affect his customer Safety testing, because his customer unit with his power supply only meet 1500Vac hipot after heating test? Only Raymond and his customers can answer this. Or what if Safety agency require his customer unit to do grounding test to accessible metal part? OK, but why? The discussions have centered around an SELV output, making the end product Class III. There would have to be some specific about the final application to justify this. We have no information to base such an assumption on. Regards, Chengwee As with many discussions on the list, practical issue discussions often get side tracked by the hypothetical and theoretical. More to the point, Raymond hasn't given us specifics on the physical orientation of parts in the power supply to any great degree. Proprietary information aside, we know: K1) the insulation between earthed parts and mains connected parts is somewhat better than Basic, but not Reinforced K2) the EST potential where breakdown occurs (though I've discarded the e-mail with the identified potential) K3) the breakdown is suspected (or possibly confirmed) to occur to the earthed board that is used as an EMC shield and which also electrically connects to an SELV output What we don't know (or I've lost track of): DK1) if the power supply is a linear or switched mode type (we can assume it's a SMPS, since EMC shielding was mentioned, but it would be nice to have confirmation) Your assumption is correct - it is a SMPS that is commonly for digital and electronics products. DK2) what mains connected part(s) are involved in the dielectric breaking down (transformer winding terminations, leads or bodies of filtering, surge suppression or other components and how they are mounted) According to Rich's suggestion, the PCB mounted AC receptacle contributes the breakdown. From the signs of breakdown, there were two places of breakdown between the mains copper tracks and earth copper track of the receptacle where have less than 5 mm spacing. DK3) what area or specific portion of the earthed parts are involved in breaking down (at solder connection points for lead wires, the copper on the shielding board) DK4) if the supply uses an appliance inlet, has a nondetachable power supply cord or if it a direct plug-in type and how the mains circuit is brought to the power conversion element(s) of the primary circuit The power is brought in via a detachable power cordset. With some of this additional information, a more practical solution may be possible, rather than talking around the specifics. A WAG or two: One issue that hasn't come up is whether or not the copper on the shielding board is facing the mains/primary circuitry or not. Based on the application and the general discussion, this board appears to be separate and independent of the mains/primary circuit board. If this is true, it seems logical that the board is single-sided. If the board is single-sided and the copper is facing the mains/primary circuit, has anyone considered flipping the board over and relying on the base laminate to provide Supplementary insulation to a clearance? The earthing plane is a separate single-sided fibre glass pcb. The copper side is not facing to the mains circuitry. If the first WAG is unusable, why not add a 0.4mm thick insulating sheet between the earthed board and the portion of the primary circuit involved in breaking down? This will effect margins and pricing, but sometimes one must bite the bullet to get into the market or meet a customer's time constraint. As explained by Rich, the class 1 AC receptacle is designed for the hi-pot of 1,500 Vac. It cannot withstand 3,000 Vac together with associated pcb tracks. Probably why the designer has to design it in that way. Such design gives challenge at final
RE: Class 1 AC/DC adapter
Peter, I am pleased to give you greater details below as required. Peter L. Tarver peter.tar...@sanmina-sci.com 05/11/03 11:40 PM Please respond to peter.tar...@sanmina-sci.com To emc-p...@ieee.org cc raymond...@omnisourceasia.com.hk, c...@netscreen.com, 'Rich Nute' ri...@sdd.hp.com Subject RE: Class 1 AC/DC adapter Let's look at these what ifs. From: ChengWee Lai Sent: Tuesday, November 04, 2003 4:38 PM Raymond might be able to convince Safety agency to accept PE continuity test with 1500Vac Hipot at the production line. However in the Scenerio with end customer, it could mean business or no business. Question regarding: Whether customer can accept his adaptor with only 1500Vac hipot tested where other power supplies can withstand 3000Vac? The only clear answer is some form of redesign is necessary. Simple solutions work best. For any reasoned advice, there are too many unknowns about the physical construction of the power supply. See the below for more on this. Would that affect his customer Safety testing, because his customer unit with his power supply only meet 1500Vac hipot after heating test? Only Raymond and his customers can answer this. Or what if Safety agency require his customer unit to do grounding test to accessible metal part? OK, but why? The discussions have centered around an SELV output, making the end product Class III. There would have to be some specific about the final application to justify this. We have no information to base such an assumption on. Regards, Chengwee As with many discussions on the list, practical issue discussions often get side tracked by the hypothetical and theoretical. More to the point, Raymond hasn't given us specifics on the physical orientation of parts in the power supply to any great degree. Proprietary information aside, we know: K1) the insulation between earthed parts and mains connected parts is somewhat better than Basic, but not Reinforced K2) the EST potential where breakdown occurs (though I've discarded the e-mail with the identified potential) K3) the breakdown is suspected (or possibly confirmed) to occur to the earthed board that is used as an EMC shield and which also electrically connects to an SELV output What we don't know (or I've lost track of): DK1) if the power supply is a linear or switched mode type (we can assume it's a SMPS, since EMC shielding was mentioned, but it would be nice to have confirmation) Your assumption is correct - it is a SMPS that is commonly for digital and electronics products. DK2) what mains connected part(s) are involved in the dielectric breaking down (transformer winding terminations, leads or bodies of filtering, surge suppression or other components and how they are mounted) According to Rich's suggestion, the PCB mounted AC receptacle contributes the breakdown. From the signs of breakdown, there were two places of breakdown between the mains copper tracks and earth copper track of the receptacle where have less than 5 mm spacing. DK3) what area or specific portion of the earthed parts are involved in breaking down (at solder connection points for lead wires, the copper on the shielding board) DK4) if the supply uses an appliance inlet, has a nondetachable power supply cord or if it a direct plug-in type and how the mains circuit is brought to the power conversion element(s) of the primary circuit The power is brought in via a detachable power cordset. With some of this additional information, a more practical solution may be possible, rather than talking around the specifics. A WAG or two: One issue that hasn't come up is whether or not the copper on the shielding board is facing the mains/primary circuitry or not. Based on the application and the general discussion, this board appears to be separate and independent of the mains/primary circuit board. If this is true, it seems logical that the board is single-sided. If the board is single-sided and the copper is facing the mains/primary circuit, has anyone considered flipping the board over and relying on the base laminate to provide Supplementary insulation to a clearance? The earthing plane is a separate single-sided fibre glass pcb. The copper side is not facing to the mains circuitry. If the first WAG is unusable, why not add a 0.4mm thick insulating sheet between the earthed board and the portion of the primary circuit involved in breaking down? This will effect margins and pricing, but sometimes one must bite the bullet to get into the market or meet a customer's time constraint. As explained by Rich, the class 1 AC receptacle is designed for the hi-pot of 1,500 Vac. It cannot withstand 3,000 Vac together with associated pcb tracks. Probably why the designer has to design it in that way. Such design gives challenge at final
Re: Class 1 AC/DC adapter
Dear Rich, Many thanks for your detail explanation that is useful to me. Raymond Li OSA Rich Nute ri...@sdd.hp.com Sent by: owner-emc-p...@majordomo.ieee.org 05/11/03 02:58 AM Please respond to Rich Nute ri...@sdd.hp.com To raymond...@omnisourceasia.com.hk cc emc-p...@ieee.org Subject Re: Class 1 AC/DC adapter Hi Raymond: If the dc output is connected to the PE terminal, then the dc output could become live in the event of a fault in the basic insulation between mains and the PE terminal. I think it may not be the case in practice. Even the dc output is connected to the PE, if the basic insulation in the earth terminal should fail, the dc output still safe. It is because the leakage current will go to the earth path (low impedance) rather than the dc output + human body path where has much higher impedance. Agreed. The situation is that the PE must be able to carry the fault current in the event of a failure of basic insulation. Consequently, the PE circuit from the furthest point where a failure of basic insulation may occur must be capable of carrying the fault current -- up to 25 amperes (according to the standard) until the mains circuit overcurrent device operates. If the PE is connected to earth, then the dc output will not rise to the mains voltage. This is the principle of protection in the event of a fault. My reference to live in the event of a fault is the principle behind the determination of what conductors must be connected to the PE terminal and must be capable of carrying 25 amperes for 1 minute. If the adapter is sealed, then the only way to test for earth continuity is to check from the dc output side to the appliance coupler earth terminal. There is a comment from the supplier that the secondary components are not supposed to handle 25A current and unforeseen damage (early failure) may happen. Any comments? The supplier is correct. However, the issue is that of testing the PE circuit after the unit is assembled. This can only be done by testing between the dc output and the PE terminal. This means that the secondary circuit path must be capable of 25-amperes for 1 minute in order to test the PE circuit. In practice, the construction you describe can indeed pass this test. The single-sided PWB earth plane has sufficient cross-sectional area to carry the 25-ampere current. The leads to the PWB from the dc output to the PWB and from the PWB to the PE terminal must be reasonably robust (e.g., 22 AWG) and short length. This prevents these conductors form overheating during the test. I've dealt with a number of these adapters and have had no problems with the 25-amp test, dc output to PE terminal. Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Class 1 AC/DC adapter
Hello Guys, Apologies for getting into many IF's. Yes, our discussion is based on assumption and description provided. There are many unknown for us on his unit. I believe the fundamental of the safety concept, which have been discussed should be look in depth by Raymond. Maybe it is time for Raymond to give us some input over the different area we discussed. Best Regards, Chengwee From: Peter L. Tarver [mailto:peter.tar...@sanmina-sci.com] Sent: Wednesday, November 05, 2003 7:40 AM To: emc-p...@ieee.org Cc: raymond...@omnisourceasia.com.hk; c...@netscreen.com; 'Rich Nute' Subject: RE: Class 1 AC/DC adapter Let's look at these what ifs. From: ChengWee Lai Sent: Tuesday, November 04, 2003 4:38 PM Raymond might be able to convince Safety agency to accept PE continuity test with 1500Vac Hipot at the production line. However in the Scenerio with end customer, it could mean business or no business. Question regarding: Whether customer can accept his adaptor with only 1500Vac hipot tested where other power supplies can withstand 3000Vac? The only clear answer is some form of redesign is necessary. Simple solutions work best. For any reasoned advice, there are too many unknowns about the physical construction of the power supply. See the below for more on this. Would that affect his customer Safety testing, because his customer unit with his power supply only meet 1500Vac hipot after heating test? Only Raymond and his customers can answer this. Or what if Safety agency require his customer unit to do grounding test to accessible metal part? OK, but why? The discussions have centered around an SELV output, making the end product Class III. There would have to be some specific about the final application to justify this. We have no information to base such an assumption on. Regards, Chengwee As with many discussions on the list, practical issue discussions often get side tracked by the hypothetical and theoretical. More to the point, Raymond hasn't given us specifics on the physical orientation of parts in the power supply to any great degree. Proprietary information aside, we know: K1) the insulation between earthed parts and mains connected parts is somewhat better than Basic, but not Reinforced K2) the EST potential where breakdown occurs (though I've discarded the e-mail with the identified potential) K3) the breakdown is suspected (or possibly confirmed) to occur to the earthed board that is used as an EMC shield and which also electrically connects to an SELV output What we don't know (or I've lost track of): DK1) if the power supply is a linear or switched mode type (we can assume it's a SMPS, since EMC shielding was mentioned, but it would be nice to have confirmation) DK2) what mains connected part(s) are involved in the dielectric breaking down (transformer winding terminations, leads or bodies of filtering, surge suppression or other components and how they are mounted) DK3) what area or specific portion of the earthed parts are involved in breaking down (at solder connection points for lead wires, the copper on the shielding board) DK4) if the supply uses an appliance inlet, has a nondetachable power supply cord or if it a direct plug-in type and how the mains circuit is brought to the power conversion element(s) of the primary circuit With some of this additional information, a more practical solution may be possible, rather than talking around the specifics. A WAG or two: One issue that hasn't come up is whether or not the copper on the shielding board is facing the mains/primary circuitry or not. Based on the application and the general discussion, this board appears to be separate and independent of the mains/primary circuit board. If this is true, it seems logical that the board is single-sided. If the board is single-sided and the copper is facing the mains/primary circuit, has anyone considered flipping the board over and relying on the base laminate to provide Supplementary insulation to a clearance? If the first WAG is unusable, why not add a 0.4mm thick insulating sheet between the earthed board and the portion of the primary circuit involved in breaking down? This will effect margins and pricing, but sometimes one must bite the bullet to get into the market or meet a customer's time constraint. Regards, Peter L. Tarver, PE ptar...@ieee.org This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher
Re: Class 1 AC/DC adapter
Hello Chengwee: Whether customer can accept his adaptor with only 1500Vac hipot tested where other power supplies can withstand 3000Vac? This is an interesting question as it implies that the higher the withstand voltage the better the unit. The statement may even imply that a double-insulation scheme provides a better safeguard against electric shock than does a PE scheme. In fact, the two schemes provide equal protection against electric shock. There is no *inherent* advantage of one over the other. The 1500-volt withstand value is derived from the normally-occuring mains-to-earth overvoltages plus margin. In other words, the 1500-volt test represents an acceptable insulation that will not fail when subjected to mains-to-earth overvoltage. The 3000-volt withstand value is derived from testing two 1500-volt insulations in series. The 3000-volt test tells us that the two insulations, as a system, are acceptable, assuming that the voltage divides equally across each insulation. (The two insulations will never see overvoltages as high as 1500 volts.) There is no inherent advantage to a unit that passes a 3000-volt withstand test versus a unit that passes a 1500-volt withstand test. The only thing that the 3000-volt withstand test tells us is that the double-insulation system is intact. If I recall correctly, Raymond Li said that the unit in question passes 3000 volts primary-to- secondary, fails 3000 volts primary-to-earth, but passes 1500-volts primary-to-earth. This tells us that both the basic insulation and the double insulation are acceptable. Would that affect his customer Safety testing, because his customer unit with his power supply only meet 1500Vac hipot after heating test? If the customer wants double-insulation throughout the unit, then the adapter is unacceptable. If the customer wants a unit that is certified to a safety standard, then the adapter is acceptable. Or what if Safety agency require his customer unit to do grounding test to accessible metal part? Based on Raymond Li's description and on my own experience, I believe there should be no problem passing the production-line grounding test at 25-amperes. * Despite the preceding comments, such an adapter should easily pass double-insulation requirements between primary and ground, and between primary and secondary. In my experience, adapters designed to IEC 60950 can easily achieve more than 4500 V rms withstand. And, they can easily achieve 25 amperes dc-to-PE. So, I am a bit disturbed that the unit does not pass 3000 V rms to earth. This says to me that there is a clearance within the unit that does not meet the IEC 60950 requirements. I would further guess that the clearance is likely to be an operator-dependent clearance that is determined during the assembly of the unit. (The IEC 60950 clearance dimensions are quite conservative, and should not break down below about 5000 V rms.) Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Class 1 AC/DC adapter
Hi Peter: I have and continue to advocate (in IEC TC 108) that such classes should apply to CIRCUITS, not to products. If this is endemic in IEC (as your statement implies), it may require a elephantine effort. Good luck. Yes. And thank you. The IEC Class I and Class II is an attempt to categorize products according to the supplemental safeguard, i.e., earthing or supplemental insulation, respectively, against electric shock. The IEC Committee that developed the class definitions is an electrical installation committee, not a product committee. I would guess that they had electrical installations, not products, in mind when they developed the definitions. Its fairly easy to encase an outlet box in metal or plastic and thereby get *pure* Class I or Class II products. With the advent of TC 108, supplemental safeguards will be treated as independent supplemental safeguards without reference to the IEC classes. I believe this will demonstrate that the IEC class designations actually confuse product design and evaluation rather than help. (This string is an example of how we get tied up with the issue of IEC Class versus actual construction!) Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Class 1 AC/DC adapter
Let's look at these what ifs. From: ChengWee Lai Sent: Tuesday, November 04, 2003 4:38 PM Raymond might be able to convince Safety agency to accept PE continuity test with 1500Vac Hipot at the production line. However in the Scenerio with end customer, it could mean business or no business. Question regarding: Whether customer can accept his adaptor with only 1500Vac hipot tested where other power supplies can withstand 3000Vac? The only clear answer is some form of redesign is necessary. Simple solutions work best. For any reasoned advice, there are too many unknowns about the physical construction of the power supply. See the below for more on this. Would that affect his customer Safety testing, because his customer unit with his power supply only meet 1500Vac hipot after heating test? Only Raymond and his customers can answer this. Or what if Safety agency require his customer unit to do grounding test to accessible metal part? OK, but why? The discussions have centered around an SELV output, making the end product Class III. There would have to be some specific about the final application to justify this. We have no information to base such an assumption on. Regards, Chengwee As with many discussions on the list, practical issue discussions often get side tracked by the hypothetical and theoretical. More to the point, Raymond hasn't given us specifics on the physical orientation of parts in the power supply to any great degree. Proprietary information aside, we know: K1) the insulation between earthed parts and mains connected parts is somewhat better than Basic, but not Reinforced K2) the EST potential where breakdown occurs (though I've discarded the e-mail with the identified potential) K3) the breakdown is suspected (or possibly confirmed) to occur to the earthed board that is used as an EMC shield and which also electrically connects to an SELV output What we don't know (or I've lost track of): DK1) if the power supply is a linear or switched mode type (we can assume it's a SMPS, since EMC shielding was mentioned, but it would be nice to have confirmation) DK2) what mains connected part(s) are involved in the dielectric breaking down (transformer winding terminations, leads or bodies of filtering, surge suppression or other components and how they are mounted) DK3) what area or specific portion of the earthed parts are involved in breaking down (at solder connection points for lead wires, the copper on the shielding board) DK4) if the supply uses an appliance inlet, has a nondetachable power supply cord or if it a direct plug-in type and how the mains circuit is brought to the power conversion element(s) of the primary circuit With some of this additional information, a more practical solution may be possible, rather than talking around the specifics. A WAG or two: One issue that hasn't come up is whether or not the copper on the shielding board is facing the mains/primary circuitry or not. Based on the application and the general discussion, this board appears to be separate and independent of the mains/primary circuit board. If this is true, it seems logical that the board is single-sided. If the board is single-sided and the copper is facing the mains/primary circuit, has anyone considered flipping the board over and relying on the base laminate to provide Supplementary insulation to a clearance? If the first WAG is unusable, why not add a 0.4mm thick insulating sheet between the earthed board and the portion of the primary circuit involved in breaking down? This will effect margins and pricing, but sometimes one must bite the bullet to get into the market or meet a customer's time constraint. Regards, Peter L. Tarver, PE ptar...@ieee.org This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Class 1 AC/DC adapter
Hello Rich, 3. I believe you will have to use 3000Vac or 4242Vdc between primary and secondary side, unless you have a failure, then there are steps to go through to isolate the failure. The adapter has basic insulation between mains and the PE terminal, and reinforced insulation between mains and the dc output. If 3000 V rms is applied between mains and the dc output (which is grounded), then 3000 V rms is also applied between mains and the PE terminal. This may lead to early failure of the basic insulation. For this reason, Class I equipment is subject to only 1500 V rms hi-pot. (If care is taken in the design such that the basic insulation has an electric strength exceeding 3000 V rms, then the 3000-V test can be applied.) Yes, it can be argue to require only basic insulation Hipot test of 1500Vac, for Class 1 unit. You and Peter have discuss in quite a lot detail on this issue, regarding the definition of PE plus countinuity test and reinforce requirement. Raymond might be able to convince Safety agency to accept PE continuity test with 1500Vac Hipot at the production line. However in the Scenerio with end customer, it could mean business or no business. Question regarding: Whether customer can accept his adaptor with only 1500Vac hipot tested where other power supplies can withstand 3000Vac? Would that affect his customer Safety testing, because his customer unit with his power supply only meet 1500Vac hipot after heating test? Or what if Safety agency require his customer unit to do grounding test to accessible metal part? Regards, Chengwee This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Class 1 AC/DC adapter
Howdy, Rich. From: Rich Nute Sent: Tuesday, November 04, 2003 2:25 PM Hi Peter: No where does the standard state that by simply providing a Functional Earth, even through an appliance inlet (implying use of a power supply cord), the equipment is not considered Class II. Unfortunately, the IEC scheme of safety, Class I, Class II, and Class III, applies to products, not to circuits. I have and continue to advocate (in IEC TC 108) that such classes should apply to CIRCUITS, not to products. If this is endemic in IEC (as your statement implies), it may require a elephantine effort. Good luck. The IEC 60950-1 standard recognizes that Class I equipment may include some Class II construction. Indeed, the standard expressly states that SELV circuits may be separated from other circuits by double or reinforced insulation and tested accordingly (although the standard does not provide guidance on segregating Class I and Class II circuits for such testing). The circuit definition approach is, at least, widely used in IEC60950-1. I suspect the equipment classes. To illustrate my point consider a simple, real world example of a Pluggable Equipment Type A, telephone key system that complies with Class II requirements throughout, but out of necessity for market requirements, must support ground start or some other telecommunications circuit where an earth is required for operation. For convenience, the earth is derived from a power supply cord at the appliance inlet. Granted, the Functional Earth would now also have to employ Reinforced or Double Insulation from Hazardous Voltage Circuits (such as Primary Circuits, a bulk ring generator's output, etc). However, for this product to necessarily be considered as Class I because the earth is derived from an earth provided through an appliance inlet is harsh, at best. The standard does not support make such a claim. With regard to testing the complete product that includes both Class I and Class II construction, i.e., hi-pot and grounding continuity, the applied tests are for Class I, not Class II. This is the point I was trying to express to Raymond Li. I agree, in general, with your EST assessment of Raymond Li's product; I only take exception to a portion of how you arrived at your conclusion. We differ primarily in the practical method for the production line earthing impedance test. Regards, Peter L. Tarver, PE ptar...@ieee.org feeling a little like AA Milne and William Goldman. This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Class 1 AC/DC adapter
Hi Chengwee: In my years working in power supply industry, I have never done the ground continuity test between Earth terminal to the DC output for adaptor. Normally I wouldn't trust the PE path with anything less than 18AWG or equivalent. There are two kinds of tests that I have in mind. First is the type test which is done during the evaluation of the unit. Second is the production- line test. For the type test, the test point can be at the site where basic insulation is interposed between the mains and the earthed conductor or part on an unassembled unit. This test does not subject the functional earth to the high current. Many cert houses require production-line ground continuity tests; some require the test current to be 25 amps. So, this test must be performed on the assembled unit and necessarily subjects the functional earth circuit to the same current as the PE circuit. In addition to that, agency such as UL have ramp up the test current to 40A, for 2 min according to the standard 2.6.3.4 for 20A circuit in U.S. As previously mentioned, as a type test, 40 A can be applied only at sites where basic insulation exists between mains and the earthed conductor or part. * The ability of the circuit to withstand high current is a function of the various resistances. The resistances, in turn, are a function of the heating that results from the current. When small conductors are used, the conductors must be short (to reduce the resistance) and heat-sunk. The construction described by Raymond Li likely uses short lengths of 18 AWG between the main board and the EMC shield. The EMC shield provides a good heat- sink for the wire. The main board also proveds heat- sinking. So, for a circuit that comprises a functional earth circuit, it can easily withstand the 25-amp production-line test. Clearly, a PE circuit requires 18 AWG or bigger wire. Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Class 1 AC/DC adapter
Hi Peter: No where does the standard state that by simply providing a Functional Earth, even through an appliance inlet (implying use of a power supply cord), the equipment is not considered Class II. One is simply limited to not marking with the aforementioned symbol. I'd appreciate hearing more from you on this Rich. Unfortunately, the IEC scheme of safety, Class I, Class II, and Class III, applies to products, not to circuits. I have and continue to advocate (in IEC TC 108) that such classes should apply to CIRCUITS, not to products. The IEC 60950-1 standard recognizes that Class I equipment may include some Class II construction. Indeed, the standard expressly states that SELV circuits may be separated from other circuits by double or reinforced insulation and tested accordingly (although the standard does not provide guidance on segregrating Class I and Class II circuits for such testing). With regard to testing the complete product that includes both Class I and Class II construction, i.e., hi-pot and grounding continuity, the applied tests are for Class I, not Class II. This is the point I was trying to express to Raymond Li. Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Class 1 AC/DC adapter
Hello Rich, Agree to the compliance thought process for PE according to the 60950 standard. In my years working in power supply industry, I have never done the ground continuity test between Earth terminal to the DC output for adaptor. Normally I wouldn't trust the PE path with anything less than 18AWG or equivalent. In addition to that, agency such as UL have ramp up the test current to 40A, for 2 min according to the standard 2.6.3.4 for 20A circuit in U.S. Chengwee From: Rich Nute [mailto:ri...@sdd.hp.com] Sent: Tuesday, November 04, 2003 10:59 AM To: raymond...@omnisourceasia.com.hk Cc: emc-p...@ieee.org Subject: Re: Class 1 AC/DC adapter Hi Raymond: If the dc output is connected to the PE terminal, then the dc output could become live in the event of a fault in the basic insulation between mains and the PE terminal. I think it may not be the case in practice. Even the dc output is connected to the PE, if the basic insulation in the earth terminal should fail, the dc output still safe. It is because the leakage current will go to the earth path (low impedance) rather than the dc output + human body path where has much higher impedance. Agreed. The situation is that the PE must be able to carry the fault current in the event of a failure of basic insulation. Consequently, the PE circuit from the furthest point where a failure of basic insulation may occur must be capable of carrying the fault current -- up to 25 amperes (according to the standard) until the mains circuit overcurrent device operates. If the PE is connected to earth, then the dc output will not rise to the mains voltage. This is the principle of protection in the event of a fault. My reference to live in the event of a fault is the principle behind the determination of what conductors must be connected to the PE terminal and must be capable of carrying 25 amperes for 1 minute. If the adapter is sealed, then the only way to test for earth continuity is to check from the dc output side to the appliance coupler earth terminal. There is a comment from the supplier that the secondary components are not supposed to handle 25A current and unforeseen damage (early failure) may happen. Any comments? The supplier is correct. However, the issue is that of testing the PE circuit after the unit is assembled. This can only be done by testing between the dc output and the PE terminal. This means that the secondary circuit path must be capable of 25-amperes for 1 minute in order to test the PE circuit. In practice, the construction you describe can indeed pass this test. The single-sided PWB earth plane has sufficient cross-sectional area to carry the 25-ampere current. The leads to the PWB from the dc output to the PWB and from the PWB to the PE terminal must be reasonably robust (e.g., 22 AWG) and short length. This prevents these conductors form overheating during the test. I've dealt with a number of these adapters and have had no problems with the 25-amp test, dc output to PE terminal. Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Class 1 AC/DC adapter
Hi John: I do have one question for the group just for my own knowledge...back in my TUV days I worked almost exclusively with IEC60950 and seem to remember that a class II product can have a functional earth connection provided Primary and other hazardous voltages are insulated from earth by reinforced insulation. In this scenario even thought the product has an earth connection would it still be considered class II with regards to the IEC60950 standard and have to be marked as such? Maybe it is semantics as you reference protective earth so it must be class I as opposed to functional earth which is not relied upon for safety. Yes, a Class II product may have a functional earth. However, the standard does not define whether that functional earth may be by means of the PE in the power cord. I have always presumed that the functional earth of a Class II product is by means of signal (functional) interconnections to other products that have their functional earth connected to their PE terminal. We don't have functional earthing through a power cord and appliance coupler. These are always built as PE conductors. The appliance coupler has basic insulation between the mains and the PE terminal. So, the use of an appliance coupler REQUIRES that the earthing circuit at the appliance coupler be a PE circuit. (Reference IEC 60950-1, sub-clause 2.6.2, last dashed paragraph.) If the product has an earthing connection via the power cord, then how do we tell the user that the earthing scheme is functional, not PE? We cannot mark the unit with the double-insulation mark. (Reference IEC 60950-1, sub-clause 2.6.2, last dashed paragraph.) My conclusion is that any product with a PE conductor or terminal (i.e., 2-wire + earth) is a Class I product. Any product without a PE conductor or terminal (i.e., 2-wire) is a Class II product. Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Class 1 AC/DC adapter
Raymond - I'm not Rich, but see the below. From: raymond...@omnisourceasia.com.hk Sent: Monday, November 03, 2003 10:18 PM Rich, If the dc output is connected to the PE terminal, then the dc output could become live in the event of a fault in the basic insulation between mains and the PE terminal. I think it may not be the case in practice. Even the dc output is connected to the PE, if the basic insulation in the earth terminal should fail, the dc output still safe. It is because the leakage current will go to the earth path (low impedance) rather than the dc output + human body path where has much higher impedance. You need to be careful not to mix requirements. The requirements for leakage current, which rely on the human body model, are not the same as those in §2.2.3, addressing maintaining SELV under fault conditions, which is the case under consideration. An accessible SELV circuit is limited to 71Vpk under any single fault condition. Unless the internal or in-building overcurrent (or other) protection can react undetectably fast (faster than a modern oscilloscope), a risk of shock would be considered to exist at the output for a mains to earth fault. Beyond compliance with the standard, one would also need to consider a fault that is not 'solid' or 'bolted.' Most real world faults have some finite impedance above those of a solid fault. In such cases, the excessive voltage might remain on the otherwise SELV circuit indefinitely. If the adapter is sealed, then the only way to test for earth continuity is to check from the dc output side to the appliance coupler earth terminal. There is a comment from the supplier that the secondary components are not supposed to handle 25A current and unforeseen damage (early failure) may happen. Any comments? In an earlier e-mail, I identified a possible method of performing the production line earthing tests on unsealed units. The act of sealing a power supply case should not have a deleterious effect on the earthing path from the Protective Earthing Terminal to the point of earthing in the SELV circuit. In this case, only the path from the protective earthing terminal to the point on the earthing transit board where it electrically connects to the SELV circuit needs to be evaluated. Testing would not need to include the output cord or other secondary circuit components. I recommend you explore this option with the safety certifier as a practical means of complying with the production line testing requirements. Regards, Peter L. Tarver, PE ptar...@ieee.org This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Class 1 AC/DC adapter
Hi Raymond: If the dc output is connected to the PE terminal, then the dc output could become live in the event of a fault in the basic insulation between mains and the PE terminal. I think it may not be the case in practice. Even the dc output is connected to the PE, if the basic insulation in the earth terminal should fail, the dc output still safe. It is because the leakage current will go to the earth path (low impedance) rather than the dc output + human body path where has much higher impedance. Agreed. The situation is that the PE must be able to carry the fault current in the event of a failure of basic insulation. Consequently, the PE circuit from the furthest point where a failure of basic insulation may occur must be capable of carrying the fault current -- up to 25 amperes (according to the standard) until the mains circuit overcurrent device operates. If the PE is connected to earth, then the dc output will not rise to the mains voltage. This is the principle of protection in the event of a fault. My reference to live in the event of a fault is the principle behind the determination of what conductors must be connected to the PE terminal and must be capable of carrying 25 amperes for 1 minute. If the adapter is sealed, then the only way to test for earth continuity is to check from the dc output side to the appliance coupler earth terminal. There is a comment from the supplier that the secondary components are not supposed to handle 25A current and unforeseen damage (early failure) may happen. Any comments? The supplier is correct. However, the issue is that of testing the PE circuit after the unit is assembled. This can only be done by testing between the dc output and the PE terminal. This means that the secondary circuit path must be capable of 25-amperes for 1 minute in order to test the PE circuit. In practice, the construction you describe can indeed pass this test. The single-sided PWB earth plane has sufficient cross-sectional area to carry the 25-ampere current. The leads to the PWB from the dc output to the PWB and from the PWB to the PE terminal must be reasonably robust (e.g., 22 AWG) and short length. This prevents these conductors form overheating during the test. I've dealt with a number of these adapters and have had no problems with the 25-amp test, dc output to PE terminal. Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Class 1 AC/DC adapter
John - IEC60950-1, §2.6.2 deals with Functional Earthing. If the earthing is functional only, it does need to be separated by Double or Reinforced Insulation, or by earthed screening and Basic Insulation, from parts at hazardous voltage. Just as for Pluggable Equipment/Class I Equipment, when an earth is brought into the equipment in a power supply cord, even if only to facilitate Functional Earthing, the double insulated symbol (IEC60417-1, Symbol 5172) can not be used. §1.2.4.1 defines Class I equipment as relying on both Basic Insulation *and* Protective Earthing. The Note to §1.2.4.1 states that Class I Equipment may also contain Double or Insulation and this appears to be the nod that Rich was referring to. No where does the standard state that by simply providing a Functional Earth, even through an appliance inlet (implying use of a power supply cord), the equipment is not considered Class II. One is simply limited to not marking with the aforementioned symbol. I'd appreciate hearing more from you on this Rich. Regards, Peter L. Tarver, PE ptar...@ieee.org From: Tyra, John Sent: Tuesday, November 04, 2003 6:30 AM Great answers Rich! I do have one question for the group just for my own knowledge...back in my TUV days I worked almost exclusively with IEC60950 and seem to remember that a class II product can have a functional earth connection provided Primary and other hazardous voltages are insulated from earth by reinforced insulation. In this scenario even thought the product has an earth connection would it still be considered class II with regards to the IEC60950 standard and have to be marked as such? Maybe it is semantics as you reference protective earth so it must be class I as opposed to functional earth which is not relied upon for safety. Regards, John Tyra This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Class 1 AC/DC adapter
Great answers Rich! I do have one question for the group just for my own knowledge...back in my TUV days I worked almost exclusively with IEC60950 and seem to remember that a class II product can have a functional earth connection provided Primary and other hazardous voltages are insulated from earth by reinforced insulation. In this scenario even thought the product has an earth connection would it still be considered class II with regards to the IEC60950 standard and have to be marked as such? Maybe it is semantics as you reference protective earth so it must be class I as opposed to functional earth which is not relied upon for safety. I have not worked with IEC60950 for some 5 years now and do not have a copy on hand as our products are UL/IEC60065 based so I apologize for the waste of bandwidth if this is an easy lookup in 950 Look forward to all answers... Regards, John Tyra Product Safety and Regulatory Compliance Manager Bose Corporation The Mountain, MS-450 Framingham, MA 01701-9168 Phone: 508-766-1502 Fax: 508-766-1145 john_t...@bose.com From: Rich Nute [mailto:ri...@sdd.hp.com] Sent: Monday, November 03, 2003 5:16 PM To: raymond...@omnisourceasia.com.hk Cc: emc-p...@ieee.org Subject: Re: Class 1 AC/DC adapter Hi Raymond: Any product with a PE (ground) connection is, by definition, a Class I product. The common adapters you describe, despite being encased in plastic, are Class I products. 1. Function of the grounding plate The primary and the secondary is reinforced insulation and withstands over 3000Vac. Is this plate to change the whole safety protection system from class 2 to class 1? Or the plate is primarily for EMC suppression? The single-sided ground-plane PCB you describe is used to control EMC emissions. It may also be used, as you describe, to electrically ground the dc output. The ground plane has no safety function, per se. While the safety standards require a product to be Class I or Class II, it is physically impossible to build a purely Class I product. Every Class I product necessarily includes Class II construction. You have accurately described the adapter Class II construction (reinforced insulation, primary-to-secondary). In other words, the adapter has both Class I construction and Class II construction. Safety standards ignore this physical true-ism. Any product with a PE is Class I, and is evaluated only to the Class I requirements. 2. Earth continuity test After the unit is completely assembled, should we conduct the test between the earth terminal of the mains plug and the earth of DC output plug? Yes. The earth continuity test is required for any accessible metal part that is susceptible of becoming live in the event of a fault of basic insulation. Within the adapter, the Class I part of the construction has basic insulation between the mains and grounded conductors. Such grounded conductors must be subject to the earth continuity test. Because the dc output is connected to the grounded conductor, the dc output could become live in the event of a fault of basic insulation. So, an earth continuity test must be conducted between the dc ground and the PE terminal of the mains connector (because the unit is sealed, the test cannot be made directly to the conductors where the fault would occur). 3. Hipot test As the unit is classified as class 1, 1,500 Vac is applied between the earth terminal of the mains female connector and the earth of the DC output plug. Actually, the primary and secondary can withstand 3000 Vac. Is it correct test voltage to apply after the unit is completely assembled? Because the unit is Class I, the hi-pot test voltage is 1500 V rms. The hi-pot test is always performed on a fully-assembled unit. You are correct that the primary-secondary reinforced insulation must withstand 3000 V rms. Note also that the primary-foil (wrapped about the outside of the adapter) must also withstand 3000 V rms (because the plastic comprises reinforced insulation to accessible surfaces). While the unit will probably withstand 3000 V rms, you should not production-line test to 3000 V rms because this may overstress the primary-ground insulation. Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable
Re: Class 1 AC/DC adapter
Rich, Many thanks for your clear explanation. I have two practical issues in below in-line message and look forward to hearing your comments. To c...@netscreen.com cc raymond...@omnisourceasia.com.hk, emc-p...@ieee.org Subject Re: Class 1 AC/DC adapter If the dc output is connected to the PE terminal, then the dc output could become live in the event of a fault in the basic insulation between mains and the PE terminal. I think it may not be the case in practice. Even the dc output is connected to the PE, if the basic insulation in the earth terminal should fail, the dc output still safe. It is because the leakage current will go to the earth path (low impedance) rather than the dc output + human body path where has much higher impedance. If the adapter is sealed, then the only way to test for earth continuity is to check from the dc output side to the appliance coupler earth terminal. There is a comment from the supplier that the secondary components are not supposed to handle 25A current and unforeseen damage (early failure) may happen. Any comments? Thanks and regards, Raymond Li OSA
Re: Class 1 AC/DC adapter
Hi Raymond: 1. Earth continuity test As the class 1 is due to the additional earthing plate, how can I ignore the earth continuity test? Class I is due to the adapter having an appliance coupler with a PE terminal. Without this earthing plate, the unit is in fact a class 2 construction. No. If the unit has a PE terminal, then the unit is Class I. The unit may be Class II construction, but if it has a PE terminal then it is a Class I product. Thus, I am a bit confused with such construction and should I follow the required safety tests for class 1 or class 2. For the purposes of testing for compliance to a safety standard, the test for Class I apply. For the purposes of true safety, then the primary- secondary insulation should be tested for Class II. I have another thought that actually, the earthing plate and the DC output plug earthing are functional earthing, not safety earthing, so electrical continuity test using multitester is sufficient and earth continuity test using low voltage and 25A current is not applicable. Yes, the earthing plate and dc output earthing are indeed functional earthing. However, they are connected to the PE, which is insulated from the mains be basic insulation. If the basic insulation should fail, then the PE becomes live. If the dc output is connected to the PE, then the dc output will become live in the event of a fault in basic insulation. In a sealed unit, the only way to test the PE portion is via the functional earthing plate and dc output terminal. So, a 25-ampere current is required to be applied between the dc functional earth terminal and the PE terminal. 2. Hi-pot test The unit passes the hi-pot test at 3,000Vac if the grounding plate and the bridging capacitor are removed. If only the bridging capacitor is removed, the test voltage goes upto about 2,100Vac max. I note that there is breakdown around the grounding plate and the pcd side of mains female connector at the max. voltage. If the unit fails the hi-pot test between the mains and the grounding plate, then the insulation between the mains and the grounding plate is basic insulation. Therefore, the grounding plate (because it is connected to an accessible part, i.e., the dc output terminal) must be connected to the PE and must pass the 25-ampere test. It seems once the production of the converter is completed, proper earth continuity test and hipot test are unable to be done at IQC of receiving warehouse. Any suggestion to do some extend of safety test without destruction of the finished goods is appreciated. The construction you describe will easily pass the tests for Class I construction, i.e., 1500-V hi-pot, and 25- ampere earthing continuity. Unfortunately, you cannot test the double insulation between mains and the dc output. Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Class 1 AC/DC adapter
Hi Chengwee Lai: 2. Earth Continuity or ground bond testing with 25A or higher is not applicable with plastic case and not applicable at the DC output side. It was meant to check the earth protection continuity of a metal chassis. Protective earthing is required for any conductive part that is susceptible of becoming live in the event of a fault. The fault is that of basic insulation. At the mains appliance coupler, the insulation between the mains and the PE terminal is basic insulation. Depending on the individual unit construction, there may be other points within the unit that comprise basic insulation between the mains and the PE terminal. If the dc output is connected to the PE terminal, then the dc output could become live in the event of a fault in the basic insulation between mains and the PE terminal. If the adapter is sealed, then the only way to test for earth continuity is to check from the dc output side to the appliance coupler earth terminal. 3. I believe you will have to use 3000Vac or 4242Vdc between primary and secondary side, unless you have a failure, then there are steps to go through to isolate the failure. The adapter has basic insulation between mains and the PE terminal, and reinforced insulation between mains and the dc output. If 3000 V rms is applied between mains and the dc output (which is grounded), then 3000 V rms is also applied between mains and the PE terminal. This may lead to early failure of the basic insulation. For this reason, Class I equipment is subject to only 1500 V rms hi-pot. (If care is taken in the design such that the basic insulation has an electric strength exceeding 3000 V rms, then the 3000-V test can be applied.) Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Class 1 AC/DC adapter
Hi Raymond: Any product with a PE (ground) connection is, by definition, a Class I product. The common adapters you describe, despite being encased in plastic, are Class I products. 1. Function of the grounding plate The primary and the secondary is reinforced insulation and withstands over 3000Vac. Is this plate to change the whole safety protection system from class 2 to class 1? Or the plate is primarily for EMC suppression? The single-sided ground-plane PCB you describe is used to control EMC emissions. It may also be used, as you describe, to electrically ground the dc output. The ground plane has no safety function, per se. While the safety standards require a product to be Class I or Class II, it is physically impossible to build a purely Class I product. Every Class I product necessarily includes Class II construction. You have accurately described the adapter Class II construction (reinforced insulation, primary-to-secondary). In other words, the adapter has both Class I construction and Class II construction. Safety standards ignore this physical true-ism. Any product with a PE is Class I, and is evaluated only to the Class I requirements. 2. Earth continuity test After the unit is completely assembled, should we conduct the test between the earth terminal of the mains plug and the earth of DC output plug? Yes. The earth continuity test is required for any accessible metal part that is susceptible of becoming live in the event of a fault of basic insulation. Within the adapter, the Class I part of the construction has basic insulation between the mains and grounded conductors. Such grounded conductors must be subject to the earth continuity test. Because the dc output is connected to the grounded conductor, the dc output could become live in the event of a fault of basic insulation. So, an earth continuity test must be conducted between the dc ground and the PE terminal of the mains connector (because the unit is sealed, the test cannot be made directly to the conductors where the fault would occur). 3. Hipot test As the unit is classified as class 1, 1,500 Vac is applied between the earth terminal of the mains female connector and the earth of the DC output plug. Actually, the primary and secondary can withstand 3000 Vac. Is it correct test voltage to apply after the unit is completely assembled? Because the unit is Class I, the hi-pot test voltage is 1500 V rms. The hi-pot test is always performed on a fully-assembled unit. You are correct that the primary-secondary reinforced insulation must withstand 3000 V rms. Note also that the primary-foil (wrapped about the outside of the adapter) must also withstand 3000 V rms (because the plastic comprises reinforced insulation to accessible surfaces). While the unit will probably withstand 3000 V rms, you should not production-line test to 3000 V rms because this may overstress the primary-ground insulation. Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Class 1 AC/DC adapter
Hi Changwee, Many thanks for your good suggestions and comments. Current difficulties in changing the design to reinforced insulation is the AC inlet which is class 1 design on the market (clearance insufficient). Is earth continuity test recommended by any safety standard in production? Regards, Raymond Li OSA ChengWee Lai c...@netscreen.com Sent by: owner-emc-p...@majordomo.ieee.org 30/10/03 02:50 AM Please respond to ChengWee Lai c...@netscreen.com To 'raymond...@omnisourceasia.com.hk' raymond...@omnisourceasia.com.hk cc EMC PSTC emc-p...@ieee.org, owner-emc-p...@majordomo.ieee.org Subject RE: Class 1 AC/DC adapter Hello Raymond, First I don't think the EMC earthing plate should be treat as reliable earthing. (require good ground continuity as welll as mechanical secure) What I will do are 1. use double insulating Bridging cap, like Y1 cap (for example Panasonic NS-A) 2. find a way to prevent the break down at the PCB location you mentioned. This in fact will make your ground plate reinforced insulated, here are some advantage from my past experience. 1. Will allow you to have a simpler production testing. 2. You don't need to explain to every customer why their system can't pass reinforce Hipot test with your power adaptor. That in return will make your adaptor hard to sell. Good luck, Chengwee Lai Netscreen Technologies, Inc Tel: +1-408-543-4126 email: c...@netscreen.com From: raymond...@omnisourceasia.com.hk mailto:raymond...@omnisourceasia.com.hk] Sent: Saturday, October 25, 2003 9:59 AM To: ChengWee Lai Cc: EMC PSTC; owner-emc-p...@majordomo.ieee.org Subject: RE: Class 1 AC/DC adapter Dear CW Lai, Many thanks for your reply useful information. I still have some queries and look forward to your further explanation. 1. Earth continuity test As the class 1 is due to the additional earthing plate, how can I ignore the earth continuity test? Without this earthing plate, the unit is in fact a class 2 construction. Thus, I am a bit confused with such construction and should I follow the required safety tests for class 1 or class 2. I have another thought that actually, the earthing plate and the DC output plug earthing are functional earthing, not safety earthing, so electrical continuity test using multitester is sufficient and earth continuity test using low voltage and 25A current is not applicable. 2. Hi-pot test The unit passes the hi-pot test at 3,000Vac if the grounding plate and the bridging capacitor are removed. If only the bridging capacitor is removed, the test voltage goes upto about 2,100Vac max. I note that there is breakdown around the grounding plate and the pcd side of mains female connector at the max. voltage. It seems once the production of the converter is completed, proper earth continuity test and hipot test are unable to be done at IQC of receiving warehouse. Any suggestion to do some extend of safety test without destruction of the finished goods is appreciated. Thanks and regards, Raymond Li OSA . ChengWee Lai c...@netscreen.com Sent by: owner-emc-p...@majordomo.ieee.org 25/10/03 02:03 AM Please respond to ChengWee Lai c...@netscreen.com To 'raymond...@omnisourceasia.com.hk' raymond...@omnisourceasia.com.hk, EMC PSTC emc-p...@ieee.org cc Subject RE: Class 1 AC/DC adapter Raymond, In regards to your question, 1. I am guessing what you meant is a seperate PCB, about the size of the power supply main PCB, either on top or on the bottom side. Copper plate on one side only. If that is the case, it was designed to lower the emission. I am not sure how effective it is, but I see people doing it. As long as there are ground connection, it would considered as class I. The plate can't be view as one of the protection in your case. 2. Earth Continuity or ground bond testing with 25A or higher is not applicable with plastic case and not applicable at the DC output side. It was meant to check the earth protection continuity of a metal chassis. 3. I believe you will have to use 3000Vac or 4242Vdc between primary and secondary side, unless you have a failure, then there are steps to go through to isolate the failure. Here is a page I made during my years in power supply industry, it should answer to many of your question. Standard reference might be old, but principle is still the same. http://www.phihong.com/html/safety_compliance.html http://www.phihong.com/html/safety_compliance.html Take care, Chengwee Lai Netscreen Technologies, Inc Tel: +1-408-543-4126 email: c...@netscreen.com From: raymond...@omnisourceasia.com.hk mailto:raymond...@omnisourceasia.com.hk] Sent: Friday, October 24, 2003 10:05 AM To: EMC PSTC Subject: Class 1 AC/DC adapter I have seem a number of class 1 AC/DC switching power supply adapters for electronic apparatus. From outlook, it looks similar to class 2 adapter - plastic case
RE: Class 1 AC/DC adapter
Mr Lai You make a very important point about not depending on a device for ground continuity that is designed only for EMI suppression. But if the power supply is failing hi-pot, the unit has a serious spacing and/or materials issue. Many power supply mfrs perform Type Tests at higher test levels than is required by the standard (to verify design margin and/or to determine actual dielectric breakdown levels). So if the unit fails a production hi-pot test, either the unit has not been installed according to the Conditions of Acceptability, or the mfr has poor QC. luck, Brian -Original Message- From: ChengWee Lai [ mailto:c...@netscreen.com] Sent: Wednesday, October 29, 2003 10:50 AM To: 'raymond...@omnisourceasia.com.hk' Cc: EMC PSTC; owner-emc-p...@majordomo.ieee.org Subject: RE: Class 1 AC/DC adapter Hello Raymond, First I don't think the EMC earthing plate should be treat as reliable earthing. (require good ground continuity as welll as mechanical secure) What I will do are 1. use double insulating Bridging cap, like Y1 cap (for example Panasonic NS-A) 2. find a way to prevent the break down at the PCB location you mentioned. This in fact will make your ground plate reinforced insulated, here are some advantage from my past experience. 1. Will allow you to have a simpler production testing. 2. You don't need to explain to every customer why their system can't pass reinforce Hipot test with your power adaptor. That in return will make your adaptor hard to sell. Good luck, Chengwee Lai Netscreen Technologies, Inc Tel: +1-408-543-4126
RE: Class 1 AC/DC adapter
Hello Raymond, First I don't think the EMC earthing plate should be treat as reliable earthing. (require good ground continuity as welll as mechanical secure) What I will do are 1. use double insulating Bridging cap, like Y1 cap (for example Panasonic NS-A) 2. find a way to prevent the break down at the PCB location you mentioned. This in fact will make your ground plate reinforced insulated, here are some advantage from my past experience. 1. Will allow you to have a simpler production testing. 2. You don't need to explain to every customer why their system can't pass reinforce Hipot test with your power adaptor. That in return will make your adaptor hard to sell. Good luck, Chengwee Lai Netscreen Technologies, Inc Tel: +1-408-543-4126 email: c...@netscreen.com From: raymond...@omnisourceasia.com.hk mailto:raymond...@omnisourceasia.com.hk] Sent: Saturday, October 25, 2003 9:59 AM To: ChengWee Lai Cc: EMC PSTC; owner-emc-p...@majordomo.ieee.org Subject: RE: Class 1 AC/DC adapter Dear CW Lai, Many thanks for your reply useful information. I still have some queries and look forward to your further explanation. 1. Earth continuity test As the class 1 is due to the additional earthing plate, how can I ignore the earth continuity test? Without this earthing plate, the unit is in fact a class 2 construction. Thus, I am a bit confused with such construction and should I follow the required safety tests for class 1 or class 2. I have another thought that actually, the earthing plate and the DC output plug earthing are functional earthing, not safety earthing, so electrical continuity test using multitester is sufficient and earth continuity test using low voltage and 25A current is not applicable. 2. Hi-pot test The unit passes the hi-pot test at 3,000Vac if the grounding plate and the bridging capacitor are removed. If only the bridging capacitor is removed, the test voltage goes upto about 2,100Vac max. I note that there is breakdown around the grounding plate and the pcd side of mains female connector at the max. voltage. It seems once the production of the converter is completed, proper earth continuity test and hipot test are unable to be done at IQC of receiving warehouse. Any suggestion to do some extend of safety test without destruction of the finished goods is appreciated. Thanks and regards, Raymond Li OSA . ChengWee Lai c...@netscreen.com Sent by: owner-emc-p...@majordomo.ieee.org 25/10/03 02:03 AM Please respond to ChengWee Lai c...@netscreen.com To 'raymond...@omnisourceasia.com.hk' raymond...@omnisourceasia.com.hk, EMC PSTC emc-p...@ieee.org cc Subject RE: Class 1 AC/DC adapter Raymond, In regards to your question, 1. I am guessing what you meant is a seperate PCB, about the size of the power supply main PCB, either on top or on the bottom side. Copper plate on one side only. If that is the case, it was designed to lower the emission. I am not sure how effective it is, but I see people doing it. As long as there are ground connection, it would considered as class I. The plate can't be view as one of the protection in your case. 2. Earth Continuity or ground bond testing with 25A or higher is not applicable with plastic case and not applicable at the DC output side. It was meant to check the earth protection continuity of a metal chassis. 3. I believe you will have to use 3000Vac or 4242Vdc between primary and secondary side, unless you have a failure, then there are steps to go through to isolate the failure. Here is a page I made during my years in power supply industry, it should answer to many of your question. Standard reference might be old, but principle is still the same. http://www.phihong.com/html/safety_compliance.html http://www.phihong.com/html/safety_compliance.html Take care, Chengwee Lai Netscreen Technologies, Inc Tel: +1-408-543-4126 email: c...@netscreen.com From: raymond...@omnisourceasia.com.hk mailto:raymond...@omnisourceasia.com.hk] Sent: Friday, October 24, 2003 10:05 AM To: EMC PSTC Subject: Class 1 AC/DC adapter I have seem a number of class 1 AC/DC switching power supply adapters for electronic apparatus. From outlook, it looks similar to class 2 adapter - plastic case. The obvious difference is that there is a grounding pcb containing a large area of copper track soldered on the solder side of master pcb. The side facing to the solder side has no copper track at all. The grounding pcb is connected to the earth terminal of the mains female connector on one end and to the earth of the DC output plug on the other end. I have following queries and seeking advice. 1. Function of the grounding plate The primary and the secondary is reinforced insulation and withstands over 3000Vac. Is this plate to change the whole safety protection system from class 2 to class 1? Or the plate is primarily for EMC suppression? 2
RE: Class 1 AC/DC adapter
Raymond - Again, assuming 60950 applies to the power supply; also assuming that by 'power adaptor,' you mean an enclosed plug-in power supply unit: If the 'earthing plate' is not required for safety reasons and provides only a functional earth, whether for EMC or other purposes, the earthing continuity or impedances tests are not required. However, if the secondaries are earthed, even for functional reasons, the product would be required to meet either electric strength testing for Reinforced Insulation or the earthing impedance test on the production line. Since you have stated the 'earthing plate' can not comply with an electric strength testing for Reinforced Insulation, the earthing impedance test would be necessary. On the basis of practical testing, it is not necessary that this test be performed after the enclosure is sealed. You should be able to negotiate with the safety certification houses to allow the earthing impedance test to be performed with the power supply unsealed, between the earthing pin, if a direct plug-in or permanently connected power supply cord, and the point of earthing in the secondary. Regards, Peter L. Tarver, PE Product Safety Manager Homologation Services Sanmina-SCI Corp. San Jose, CA peter.tar...@sanmina-sci.com From: raymond...@omnisourceasia.com.hk Sent: Saturday, October 25, 2003 9:59 AM Dear CW Lai, Many thanks for your reply useful information. I still have some queries and look forward to your further explanation. 1. Earth continuity test As the class 1 is due to the additional earthing plate, how can I ignore the earth continuity test? Without this earthing plate, the unit is in fact a class 2 construction. Thus, I am a bit confused with such construction and should I follow the required safety tests for class 1 or class 2. I have another thought that actually, the earthing plate and the DC output plug earthing are functional earthing, not safety earthing, so electrical continuity test using multitester is sufficient and earth continuity test using low voltage and 25A current is not applicable. 2. Hi-pot test The unit passes the hi-pot test at 3,000Vac if the grounding plate and the bridging capacitor are removed. If only the bridging capacitor is removed, the test voltage goes upto about 2,100Vac max. I note that there is breakdown around the grounding plate and the pcd side of mains female connector at the max. voltage. It seems once the production of the converter is completed, proper earth continuity test and hipot test are unable to be done at IQC of receiving warehouse. Any suggestion to do some extend of safety test without destruction of the finished goods is appreciated. Thanks and regards, Raymond Li OSA This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Class 1 AC/DC adapter
Dear CW Lai, Many thanks for your reply useful information. I still have some queries and look forward to your further explanation. 1. Earth continuity test As the class 1 is due to the additional earthing plate, how can I ignore the earth continuity test? Without this earthing plate, the unit is in fact a class 2 construction. Thus, I am a bit confused with such construction and should I follow the required safety tests for class 1 or class 2. I have another thought that actually, the earthing plate and the DC output plug earthing are functional earthing, not safety earthing, so electrical continuity test using multitester is sufficient and earth continuity test using low voltage and 25A current is not applicable. 2. Hi-pot test The unit passes the hi-pot test at 3,000Vac if the grounding plate and the bridging capacitor are removed. If only the bridging capacitor is removed, the test voltage goes upto about 2,100Vac max. I note that there is breakdown around the grounding plate and the pcd side of mains female connector at the max. voltage. It seems once the production of the converter is completed, proper earth continuity test and hipot test are unable to be done at IQC of receiving warehouse. Any suggestion to do some extend of safety test without destruction of the finished goods is appreciated. Thanks and regards, Raymond Li OSA . ChengWee Lai c...@netscreen.com Sent by: owner-emc-p...@majordomo.ieee.org 25/10/03 02:03 AM Please respond to ChengWee Lai c...@netscreen.com To 'raymond...@omnisourceasia.com.hk' raymond...@omnisourceasia.com.hk, EMC PSTC emc-p...@ieee.org cc Subject RE: Class 1 AC/DC adapter Raymond, In regards to your question, 1. I am guessing what you meant is a seperate PCB, about the size of the power supply main PCB, either on top or on the bottom side. Copper plate on one side only. If that is the case, it was designed to lower the emission. I am not sure how effective it is, but I see people doing it. As long as there are ground connection, it would considered as class I. The plate can't be view as one of the protection in your case. 2. Earth Continuity or ground bond testing with 25A or higher is not applicable with plastic case and not applicable at the DC output side. It was meant to check the earth protection continuity of a metal chassis. 3. I believe you will have to use 3000Vac or 4242Vdc between primary and secondary side, unless you have a failure, then there are steps to go through to isolate the failure. Here is a page I made during my years in power supply industry, it should answer to many of your question. Standard reference might be old, but principle is still the same. http://www.phihong.com/html/safety_compliance.html http://www.phihong.com/html/safety_compliance.html Take care, Chengwee Lai Netscreen Technologies, Inc Tel: +1-408-543-4126 email: c...@netscreen.com From: raymond...@omnisourceasia.com.hk mailto:raymond...@omnisourceasia.com.hk] Sent: Friday, October 24, 2003 10:05 AM To: EMC PSTC Subject: Class 1 AC/DC adapter I have seem a number of class 1 AC/DC switching power supply adapters for electronic apparatus. From outlook, it looks similar to class 2 adapter - plastic case. The obvious difference is that there is a grounding pcb containing a large area of copper track soldered on the solder side of master pcb. The side facing to the solder side has no copper track at all. The grounding pcb is connected to the earth terminal of the mains female connector on one end and to the earth of the DC output plug on the other end. I have following queries and seeking advice. 1. Function of the grounding plate The primary and the secondary is reinforced insulation and withstands over 3000Vac. Is this plate to change the whole safety protection system from class 2 to class 1? Or the plate is primarily for EMC suppression? 2. Earth continuity test After the unit is completely assembled, should we conduct the test between the earth terminal of the mains plug and the earth of DC output plug? 3. Hipot test As the unit is classified as class 1, 1,500 Vac is applied between the earth terminal of the mains female connector and the earth of the DC output plug. Actually, the primary and secondary can withstand 3000 Vac. Is it correct test voltage to apply after the unit is completely assembled? Thanks and regards, Raymond Li OSA
RE: Class 1 AC/DC adapter
In event of single fault condition, the accessible conductive parts become hazardous, and the protection is provided by Earth ground. Then yes, ground bond test to confirm the continuity of protection by earth ground. On the other hand if single fault harzadous voltage accessible conductive part not protect by earth ground, it will be considered as a failure. Chengwee From: john.radom...@modicon.com [mailto:john.radom...@modicon.com] Sent: Friday, October 24, 2003 12:45 PM To: ChengWee Lai Cc: EMC PSTC Subject: RE: Class 1 AC/DC adapter Earth Continuity or ground bond testing with 25A or higher is not applicable with plastic case and not applicable at the DC output side. It was meant to check the earth protection continuity of a metal chassis. The bond test is applicable to any accessible conductive parts that might assume a HAZARDOUS VOLTAGE in the event of a single fault, not only to chassis. John Radomski Principal Engineer Schneider Electric ChengWee Lai c...@netscreen.com To: 'raymond...@omnisourceasia.com.hk' raymond...@omnisourceasia.com.hk, EMC Sent by: PSTC emc-p...@ieee.org owner-emc-pstc@majordocc: mo.ieee.org Subject: RE: Class 1 AC/DC adapter 10/24/2003 02:03 PM Please respond to ChengWee Lai Raymond, In regards to your question, 1. I am guessing what you meant is a seperate PCB, about the size of the power supply main PCB, either on top or on the bottom side. Copper plate on one side only. If that is the case, it was designed to lower the emission. I am not sure how effective it is, but I see people doing it. As long as there are ground connection, it would considered as class I. The plate can't be view as one of the protection in your case. 2. Earth Continuity or ground bond testing with 25A or higher is not applicable with plastic case and not applicable at the DC output side. It was meant to check the earth protection continuity of a metal chassis. 3. I believe you will have to use 3000Vac or 4242Vdc between primary and secondary side, unless you have a failure, then there are steps to go through to isolate the failure. Here is a page I made during my years in power supply industry, it should answer to many of your question. Standard reference might be old, but principle is still the same. http://www.phihong.com/html/safety_compliance.html Take care, Chengwee Lai Netscreen Technologies, Inc Tel: +1-408-543-4126 email: c...@netscreen.com -Original Message- From: raymond...@omnisourceasia.com.hk [mailto:raymond...@omnisourceasia.com.hk] Sent: Friday, October 24, 2003 10:05 AM To: EMC PSTC Subject: Class 1 AC/DC adapter I have seem a number of class 1 AC/DC switching power supply adapters for electronic apparatus. From outlook, it looks similar to class 2 adapter - plastic case. The obvious difference is that there is a grounding pcb containing a large area of copper track soldered on the solder side of master pcb. The side facing to the solder side has no copper track at all. The grounding pcb is connected to the earth terminal of the mains female connector on one end and to the earth of the DC output plug on the other end. I have following queries and seeking advice. 1. Function of the grounding plate The primary and the secondary is reinforced insulation and withstands over 3000Vac. Is this plate to change the whole safety protection system from class 2 to class 1? Or the plate is primarily for EMC suppression? 2. Earth continuity test After the unit is completely assembled, should we conduct the test between the earth terminal of the mains plug and the earth of DC output plug? 3. Hipot test As the unit is classified as class 1, 1,500 Vac is applied between the earth terminal of the mains female connector and the earth of the DC output plug. Actually, the primary and secondary can withstand 3000 Vac. Is it correct test voltage to apply after the unit is completely assembled? Thanks and regards, Raymond Li OSA This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri
RE: Class 1 AC/DC adapter
Earth Continuity or ground bond testing with 25A or higher is not applicable with plastic case and not applicable at the DC output side. It was meant to check the earth protection continuity of a metal chassis. The bond test is applicable to any accessible conductive parts that might assume a HAZARDOUS VOLTAGE in the event of a single fault, not only to chassis. John Radomski Principal Engineer Schneider Electric ChengWee Lai c...@netscreen.com To: 'raymond...@omnisourceasia.com.hk' raymond...@omnisourceasia.com.hk, EMC Sent by: PSTC emc-p...@ieee.org owner-emc-pstc@majordocc: mo.ieee.org Subject: RE: Class 1 AC/DC adapter 10/24/2003 02:03 PM Please respond to ChengWee Lai Raymond, In regards to your question, 1. I am guessing what you meant is a seperate PCB, about the size of the power supply main PCB, either on top or on the bottom side. Copper plate on one side only. If that is the case, it was designed to lower the emission. I am not sure how effective it is, but I see people doing it. As long as there are ground connection, it would considered as class I. The plate can't be view as one of the protection in your case. 2. Earth Continuity or ground bond testing with 25A or higher is not applicable with plastic case and not applicable at the DC output side. It was meant to check the earth protection continuity of a metal chassis. 3. I believe you will have to use 3000Vac or 4242Vdc between primary and secondary side, unless you have a failure, then there are steps to go through to isolate the failure. Here is a page I made during my years in power supply industry, it should answer to many of your question. Standard reference might be old, but principle is still the same. http://www.phihong.com/html/safety_compliance.html Take care, Chengwee Lai Netscreen Technologies, Inc Tel: +1-408-543-4126 email: c...@netscreen.com -Original Message- From: raymond...@omnisourceasia.com.hk [mailto:raymond...@omnisourceasia.com.hk] Sent: Friday, October 24, 2003 10:05 AM To: EMC PSTC Subject: Class 1 AC/DC adapter I have seem a number of class 1 AC/DC switching power supply adapters for electronic apparatus. From outlook, it looks similar to class 2 adapter - plastic case. The obvious difference is that there is a grounding pcb containing a large area of copper track soldered on the solder side of master pcb. The side facing to the solder side has no copper track at all. The grounding pcb is connected to the earth terminal of the mains female connector on one end and to the earth of the DC output plug on the other end. I have following queries and seeking advice. 1. Function of the grounding plate The primary and the secondary is reinforced insulation and withstands over 3000Vac. Is this plate to change the whole safety protection system from class 2 to class 1? Or the plate is primarily for EMC suppression? 2. Earth continuity test After the unit is completely assembled, should we conduct the test between the earth terminal of the mains plug and the earth of DC output plug? 3. Hipot test As the unit is classified as class 1, 1,500 Vac is applied between the earth terminal of the mains female connector and the earth of the DC output plug. Actually, the primary
RE: Class 1 AC/DC adapter
I am assuming that you are attempting to comply with 60950... First, please observe the Conditions of Acceptibility stated in the manufacurer's installation instructions. If the mfr says the p.s. is a Class 1 device, the end-installation must be conform to Class 1, or you must provide an enclosure and limiting circuits that allow Class 2 use. Di-electric withstand Type Test levels for the p.s. are determined by class of required insulation and measured Working Voltage. Routine test levels for the p.s. may not be reduced in magnitude, only in time. 60950 infers the requirement to perform di-electric withstand for Routine Test in note 1 of clause 5.2.2, for all Type Tests required by the standard. So you do need to do hi-pot from input to output, and from input to chassis and/or enclosure. luck, Brian -Original Message- From: raymond...@omnisourceasia.com.hk [ mailto:raymond...@omnisourceasia.com.hk] Sent: Friday, October 24, 2003 10:05 AM To: EMC PSTC Subject: Class 1 AC/DC adapter I have seem a number of class 1 AC/DC switching power supply adapters for electronic apparatus. From outlook, it looks similar to class 2 adapter - plastic case. The obvious difference is that there is a grounding pcb containing a large area of copper track soldered on the solder side of master pcb. The side facing to the solder side has no copper track at all. The grounding pcb is connected to the earth terminal of the mains female connector on one end and to the earth of the DC output plug on the other end. I have following queries and seeking advice. 1. Function of the grounding plate The primary and the secondary is reinforced insulation and withstands over 3000Vac. Is this plate to change the whole safety protection system from class 2 to class 1? Or the plate is primarily for EMC suppression? 2. Earth continuity test After the unit is completely assembled, should we conduct the test between the earth terminal of the mains plug and the earth of DC output plug? 3. Hipot test As the unit is classified as class 1, 1,500 Vac is applied between the earth terminal of the mains female connector and the earth of the DC output plug. Actually, the primary and secondary can withstand 3000 Vac. Is it correct test voltage to apply after the unit is completely assembled? Thanks and regards, Raymond Li OSA
RE: Class 1 AC/DC adapter
Raymond, In regards to your question, 1. I am guessing what you meant is a seperate PCB, about the size of the power supply main PCB, either on top or on the bottom side. Copper plate on one side only. If that is the case, it was designed to lower the emission. I am not sure how effective it is, but I see people doing it. As long as there are ground connection, it would considered as class I. The plate can't be view as one of the protection in your case. 2. Earth Continuity or ground bond testing with 25A or higher is not applicable with plastic case and not applicable at the DC output side. It was meant to check the earth protection continuity of a metal chassis. 3. I believe you will have to use 3000Vac or 4242Vdc between primary and secondary side, unless you have a failure, then there are steps to go through to isolate the failure. Here is a page I made during my years in power supply industry, it should answer to many of your question. Standard reference might be old, but principle is still the same. http://www.phihong.com/html/safety_compliance.html Take care, Chengwee Lai Netscreen Technologies, Inc Tel: +1-408-543-4126 email: c...@netscreen.com From: raymond...@omnisourceasia.com.hk mailto:raymond...@omnisourceasia.com.hk] Sent: Friday, October 24, 2003 10:05 AM To: EMC PSTC Subject: Class 1 AC/DC adapter I have seem a number of class 1 AC/DC switching power supply adapters for electronic apparatus. From outlook, it looks similar to class 2 adapter - plastic case. The obvious difference is that there is a grounding pcb containing a large area of copper track soldered on the solder side of master pcb. The side facing to the solder side has no copper track at all. The grounding pcb is connected to the earth terminal of the mains female connector on one end and to the earth of the DC output plug on the other end. I have following queries and seeking advice. 1. Function of the grounding plate The primary and the secondary is reinforced insulation and withstands over 3000Vac. Is this plate to change the whole safety protection system from class 2 to class 1? Or the plate is primarily for EMC suppression? 2. Earth continuity test After the unit is completely assembled, should we conduct the test between the earth terminal of the mains plug and the earth of DC output plug? 3. Hipot test As the unit is classified as class 1, 1,500 Vac is applied between the earth terminal of the mains female connector and the earth of the DC output plug. Actually, the primary and secondary can withstand 3000 Vac. Is it correct test voltage to apply after the unit is completely assembled? Thanks and regards, Raymond Li OSA
