In message
<camsb7hsnbuxus1fwguu9em2oo-vqjxvagdxqb8jnwbwpfo5...@mail.gmail.com>,
dated Wed, 23 Oct 2013, Pat Lawler <[email protected]> writes:
Do the EMC test standards require one of the AC input phases ('neutral'
in the U.S.) be grounded? If so, where can I find an example of this
requirement?
I can't recall any specific provision, but the testing must be done
under conditions that are as realistic as possible, and a balanced mains
supply does not qualify unless the product is specifically intended to
be operated from such a supply.
In the past, I had an experience where EMI test results with an AC
supply of 120Vac/0Vac (a source with a grounded neutral) were higher
than an AC supply of +60Vac/-60Vac (a source from an isolation
transformer.) I changed my test setup to use a grounded neutral to
agree with installation practices.
Now I have to justify this to someone, and would like some supporting
paperwork. It's not easy justifying something that may uncover
problems.
See above.
Also, does the AC voltage supplied to homes & small businesses in
Europe have a grounded phase, or are both phases above ground?
It is somewhat different in different countries. In many, the neutral is
grounded at the service entrance. In Britain and in some other
countries, the neutral is grounded only in the supplier's cables, in
many places.
There are regions in Europe where ground conductivity is poor, and a
'TT' distribution system is used, where the neutral is grounded through
an impedance at the sub-station and nowhere else. You do not have to
take this into account in EMC tests.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
If dictionaries were correct, we would only need one, because they would all
give the same information.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
-
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