I fully agree with John W on the SELV/PELV nomenclature - it is a nonsense
at the moment.
It is very confusing for most people to use the same term (SELV) in
different standards to mean different things, and very difficult to explain
to someone who doesnt appreciate the considerable differences in
construction that generally arise - we should use PELV in all the standards
where we actually mean earthed SELV.
Regards
John Allen
----- Original Message -----
From: "John Woodgate" <j...@jmwa.demon.co.uk>
To: <emc-p...@majordomo.ieee.org>
Sent: Saturday, December 06, 2003 4:00 PM
Subject: Re: How do I do this test?
>
> I read in !emc-pstc that Rich Nute <ri...@sdd.hp.com> wrote (in
> <200312051737.jaa27...@epgc264.sdd.hp.com>) about 'How do I do this
> test?' on Fri, 5 Dec 2003:
>
> > At one time, using SELV earthing as a
> > supplementary protection scheme was not
> > allowed in some countries. I'm not sure of
> > the current situation.
>
> My understanding is that IEC 60950 uses a definition of 'SELV' that
> allows it to be earthed, whereas other standards require that SELV is
> NOT earthed but floating. IMHO, the latter is dangerous because an
> undetected fault can put that floating SELV circuit at a hazardous
> voltage with no fault being apparent until someone touches or earths the
> SELV circuit.
>
> Other standards than 60950 have introduced 'PELV' ('Protected...') to
> mean a circuit which is both 'double-insulated' and earthed. I think
> this is a better term than 'earthed SELV' for the reasons explained
> above.
> --
> Regards, John Woodgate, OOO - Own Opinions Only.
http://www.jmwa.demon.co.uk
> Interested in professional sound reinforcement and distribution? Then go
to
> http://www.isce.org.uk
> PLEASE do NOT copy news posts to me by E-MAIL!
>
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