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 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
