The obvious question I would have is... why couldn't you test at a higher current for longer time meeting both requirements? For example 30A for two minutes. I know the document indicates a maximum current, but does this make sense?
Works for me. I can't imagine any agency refusing to accept a 30A test for 2 min, versus a 25A test for 1 min. Just one small caution: the pass/fail requirements are similar, but not the same. The 25A test (IEC) sets an impedance limit of 0.1 ohms; the 30A test (CSA) sets a voltage drop limit of 4V (ie. 0.133 ohms). So it is possible to pass the CSA test and fail the IEC test. Not very probable, though.
Personally, I don't get too excited about whether you want to test at 25A or 30A, as long as the earthing path is of sound construction. The difference is trivial. That is, if the intended circuit is a 15A branch circuit. Consider however a machine that operates from, say, a 100A circuit. In that case, I ask myself: "What is the bloody point?" I mean, if the device is designed to operate at 100A, it seems kind of silly to allow a ground path that can only handle 25A!
In this regard, I think that the CSA standard is a little bit better though out. The required test is at twice the branch circuit protection, for as long as it takes the breaker to open. Seems much more sensible to me. By the way, if you take a peek at IEC 60950, 3rd Edition, you will see that IEC is finally leaning towards this rationale.
By the way, CSA 0.4 is required not only in Canada, but also in the US. Since both countries have adopted the same binational CSA950/UL1950 standard, and since CSA 0.4 is specifically required by this standard, this has become an official requirement for the US. This is an unequivocal requirement, so I have no doubt that all US safety agencies are diligently performing the CSA tests.
Egon :-) __________________________________________ Egon H. Varju, PEng E.H. Varju & Associates Ltd. North Vancouver, Canada Tel: 1 604 985 5710 HAVE MODEM Fax: 1 604 273 5815 WILL TRAVEL E-mail: [email protected] [email protected] __________________________________________ --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
