Re: [PSES] IEC 61000-4-5 Surge Testing Single plug vs. multiple plug system

[John Woodgate]

I feel sure that

/"When testing line to ground, the lines are tested singly in sequence, 
if there is no other/
/specification."/
is about 3-phase supplies, not multiple mains leads.

Best wishes
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK

On 2019-01-03 01:15, John Howe wrote:
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 <j...@woodjohn.uk 
<mailto:j...@woodjohn.uk>> 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 Associateswww.woodjohn.uk  <http://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
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*John M. Howe
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