John -
You mention requirements for impedance of 0.1 Ohm, including the line cord, fuse and earthing path inside the product. Which standard(s) are you basing this on? I ask because the line cord and fuse is not taken into account in 60950/60950-1 and variants, which measure between accessible conductive parts likely to become energized back to the PE terminal. Somewhat different in 60601-1 (mind you, I'm referring to the UL version here), earthing impedance is measure between accessible conductive parts to either the appliance inlet contact for products with removable power supply cords; to the earthing terminal of a nondetachable power supply cord, but the impedance limit is increased to 0.2 Ohm [some additional considerations apply for some constructions]. It would be an interesting exercise to get as many of these difference between stands out on the table, if others are willing to provide their knowledge of additional standards. I wonder if this will be an item of contention in TC108, as IEC60065 and IEC60950-1 are blended into the hazard based standard. Regards, Peter L. Tarver, PE Product Safety Manager Homologation Services Sanmina-SCI Corp. San Jose, CA [email protected] > From: John Woodgate > Sent: Thursday, September 11, 2003 2:50 PM > > > For safety, the requirements are a low enough > impedance at the power > supply frequency |(50 or 60 Hz, usually), and > sufficient current- > carrying capacity (typically 25 A for a few > hundred milliseconds). The > impedance requirement (applied to the whole > primary supply) is usually > more difficult to meet, being typically 0.1 ohm, > including the mains > cable, fuse and internal wiring, but assuming a > zero-impedance short- > circuit between (live + neutral) and earth. > -- > Regards, John Woodgate 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] 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
