IEC 61000-4-5 (2005) does cover this and implies in section 8.3 (page 38 in my copy): "In the case of several identical circuits, representative measurements (plural) on a selected number of circuits may be sufficient. " and further down: "When testing line to ground, the lines are tested singly in sequence, if there is no other specification."
>From testing experience the only out we had for a client to test them all together (usually because they did not want to pay for individual testing) was if they were designed to be plugged into the same circuit breaker - which kind of defeats the purpose of having multiple cords. If you think about it if the cords are plugged into different circuits then the surge path to the individual cords can be different and you should not model it as equal on all cords - it could be out of phase as much as 180 degrees giving twice the surge across 2 cords. So keeping the other plugs at normal while the one cord is tested seems to be good practice. My opinions only and not necessarily those of the company I work for.... On Wed, Jan 2, 2019 at 3:35 PM John Woodgate <[email protected]> wrote: > Should you be testing a 'system' as a whole anyway? My take on this is > that if several pieces of equipment are invoiced together with a single > price for the lot, that is a system and all must be tested together. But if > the pieces are invoiced separately (so that other equipment might be > substituted for some in another instance), that is not a system and the > pieces should be tested separately. > > The authors of 61000-4-5 and 61326-x might well not have addressed the > case of multiple power cords. The test house 'advice' seems reasonable, but > it is not official and another test house might offer other advice. > > Best wishes > John Woodgate OOO-Own Opinions Only > J M Woodgate and Associates www.woodjohn.uk > Rayleigh, Essex UK > > On 2019-01-02 22:15, Larry K. Stillings wrote: > > All, > > > > I received the following email from a customer today via their customer > addressing our application of surge testing. We are testing laboratory > equipment per IEC/EN 61326-1 and IEC/EN 61326-2-6 and specifically are > having failures with respect to surge on a system that has multiple power > cords. We are testing one power cord at a time. Here are their comments > > > > *we have never tested a system comprised of multiple instruments in this > way before. i.e. applying surge to one unit at a time – we have always, > with agreement from our customers, applied surge (and in fact all tests) to > all of the units plugged into e.g. a mains distribution block all at the > same time. Especially for surge, it seems unlikely that in the real world > any real surge on the mains supply would not affect all things in a system > as it is very likely they are all plugged into the same mains circuit in > e.g a particular room. To further bolster this, we have made comment to > customers in the past that it could be noted in the manual to ensure this > is the case.* > > > > * By applying surge to all units at the same time, we maintain all of > their supply voltages at the same level. I can see how, by applying a surge > to a single part of the wider system, communications issues could occur as > suddenly the points of reference (i.e. reference voltages) for different > parts of the system could be pulled away from each other by the surge.* > > > > *Testing a system by applying the tests to all at once, rather than a > single item at a time, isn’t necessarily an “easy way out“ either. For > other tests e.g. conducted emissions, where noise transmitted from the unit > under test back onto the mains supply is measured, passing is made more > difficult by measuring all units at once. Where in this case one at a time > would be much more favourable. Our test house has always advised that we > can choose, either all tests one at a time, or all tests applied to all > through a mains block, but we cannot mix and match between different > sections for the conducted EMC tests.* > > > > I know this brings up all sorts of questions, however I would like to > focus on the surge testing at the moment. I am pretty sure at least one of > the standards says conducted emissions shall be tested on each port > individually, but we don’t need to go there right now ;-) > > > > Thoughts when you get responses like this? > > Larry K. Stillings > Compliance Worldwide, Inc. > *Test Locally, Sell Globally and Launch Your Products Around the World!* > *FCC - Wireless - Telecom - CE Marking - International Approvals - Product > Safety* > 357 Main Street > Sandown, NH 03873 > (603) 887 3903 Fax 887-6445 > www.complianceworldwide.com > > Privileged/Confidential Information may be contained in this message. 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