Rich Nute said : - For grounded (Class I) equipment for the home, the UL leakage current is 0.5 mA. (This is NOT a 60950 limit.)
UL reasoned that if 0.5 mA arises from both real and stray capacitance, then, for double-insulated (Class II) equipment, the current should be one-half of 0.5 mA because the standard requires the same insulation to be applied again (i.e., the second half of double insulation), thus halving the capacitance. Half of the capacitance results in half of the current, therefore 0.25 mA. UL carried this concept from their generic double-insulation standard into IEC 60950. -------------------------------------------------------------------- Surely the 0.25mA for Class II products was just copied from IEC380 into IEC 60950 ? I also note that in my copy of ANSI C101-1992, standard for leakage current for appliances, that the limit for 2 wire appliances is the same as for 3 wire appliances, namely 0.5 MIU = 0.5 mA. Regards John Crabb, Development Excellence (Product Safety) , NCR Financial Solutions Group Ltd., Discovery Centre, 3 Fulton Road, Dundee, Scotland, DD2 4SW E-Mail :[email protected] Tel: +44 (0)1382-592289 (direct ). Fax +44 (0)1382-622243. - > > Touch current limit for accessible parts and circuits not connected > > to protective earth: 0.25 mA > > question 1 : How does it (0.25mA) come from and what it is based on? The UL reasoning is faulty because in real life the two capacitances need not be equal. And, this is certainly not the case for reinforced insulation. Furthermore, the current, 0.5 mA, is deemed acceptable in terms of the safe current that can be applied to the body. Therefore, the 0.25 mA limit is not related to the effects of the current on the body, but presumes a product construction comprised of double insulation where each insulation system provides exactly the same capacitance. 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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"
