Hi John:
> I read in !emc-pstc that Crabb, John <jo...@exchange.scotland.ncr.com>
> wrote (in <B6CD5947CF30D411A1350050DA4B75FF03C2341C@sgbdun200.scotland.n
> cr.com>) about 'South Korean Power System', on Wed, 20 Feb 2002:
> >Typically I would expect IT equipment to be safe if line and neutral
> >were reversed, except for the issues relating to a single pole
> >disconnect device and fusing.
>
> See Tables 2E and 2F in IEC/EN60950:2000. Double-pole switching and
> fusing is almost always necessary in practice.
Tables 2E and 2F are invoked only by the Note 2
to Sub-clause 2.7.4.
A Note is informative, not a requirement.
Note 2 specifically addresses the situation where
protection devices are integral to the equipment.
It further states that the examples are not
necessarily valid for protective devices in the
building installation.
For earth faults in plug-and-socket-connected
equipment, the equipment need not include double-pole
fusing as the protective device in the building
installation provides the earth-fault protection.
This is the basis for the robustness requirements
of the equipment protective earthing circuit.
So, in practice, double-pole fusing is seldom
necessary.
Double-pole switching, on the other hand, is almost
always necessary in practice. The exception is
where both the supply and the equipment connection
to the supply are polarized, in which case a single-
pole switch in the phase conductor is acceptable.
Best regards,
Rich
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