Paul, Table 2N of UL 60950 applies to Creepage (spacing along the surface of a PWB), not Clearance (through air) on a suitably coated PWB. Keep in mind that you have to jump through some test hoops in order to use these reduced spacings. If the pins on the connector are not suitably coated, you have to use the values in Table 2K per my comments below.
To determine Clearance, it's necessary to know the following variables: - Circuit type (hazardous, SELV, TNV, limited current, etc.) - Insulation Type (Functional, Basic, Supplementary, Double, Reinforced; see Table 2G) - Peak voltage across the insulation - Nominal mains supply voltage (I'm assuming it's -48 Vdc in this case) - Telecommunication network transient voltage (800 V for TNV-2, 1500 V for TNV-1 or TNV-3, or 2500 V) - Pollution Degree (1, 2, or 3) With these values, go to Table 2K (in the case of Secondary Circuits) to determine the minimum Clearance. To determine Creepage (spacing on the surface of the PWB), it's necessary to know the following variables: - Circuit type (hazardous, SELV, TNV, limited current, etc.) - Insulation Type (Functional, Basic, Supplementary, Double, Reinforced; see Table 2G) - RMS voltage across the insulation - Pollution Degree (1, 2, or 3) - Material Group (I, II, III, IIIA, IIIB) With these values, go to Table 2L to determine the minimum Creepage. Distance through insulation is more straightforward, you need to know: - Circuit type (hazardous, SELV, TNV, limited current, etc.) - Insulation Type (Functional, Basic, Supplementary, Double, Reinforced; see Table 2G) - Peak Working Voltage If the Peak Working Voltage does not exceed 71 V, there is no requirement for distance through insulation. If the Peak Working Voltage exceeds 71 V, the following rules apply: - For Functional Insulation and Basic Insulation there is no requirement at any Peak Working Voltage for distance through insulation; - Supplementary Insulation or Reinforced Insulation shall have a minimum distance through insulation of 0,4 mm. As you can see from the above, there are many combinations involved. There is no simple rule of thumb, you have to go through the exercise for each circuit type. I find it helpful to come up with a matrix listing the circuit type on the x and y axis, then fill in the required Insulation Type, and then the required spacing. Do this for Clearance, Creepage, and Distance Through Insulation. Hope this helps. Best regards, Dave Lorusso Lorusso Technologies, LLC "Your NEBS, Product Safety and EMC Solution" www.lorusso.com 512.695.5871 (phone) 512.233.2939 (fax) -----Original Message----- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Denomme, Paul S. Sent: Monday, October 21, 2002 3:21 PM To: emc-p...@majordomo.ieee.org Subject: Clearance requirements for Telecomm PWB design I am hoping someone out there can give me a bit of help. I am currently working on a design for the telecom industry. I need to determine the minimum specifications for setting up my design rules for both internal and external layers and connector selection. According to UL60950 table 2N the minimum clearance that I need to adhere to is .2mm (voltages up to and including 125 V r.m.s or DC). This translates to a 008" clearance. Will this be acceptable? I also expect that a connector (press-fit) into this board will have to meet or exceed this minimum clearance between any two conductive surfaces or do I need to refer to Table 2K , Pollution degree1 & 2, Voltages under 71VDC 50 Vr.m.s.? Finally almost all specifications are expressed through insulation whether Functional , Basic / Supplementary, or Reinforced. Does this clearance need to grow through air dielectric? Regards, Paul S. Denomme Paul S. Denomme Backplane Design Engineer Viasystems Technologies Inc. Richmond, VA 23235 804-226-5155 ------------------------------------------- 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: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" ------------------------------------------- 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: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
