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
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