> It is important to switch all three power leads, not just the
> hot lead,
> because neutrals from separate sources cannot be made common-
> especially
> when a separately-derived power source is involved- and the equipment
> grounds must guide any fault current back to the source via
> the most direct
> route, which is alongside the respective hot conductor.
Eric, you probably have more experience with industrial electrical than I
do, but I can't recall anywhere in NEC where switching EGC is permitted,
even with separately-derived systems. My copy of NEC is back at the shop,
maybe you have yours handy and can provide a reference for my own
edjumication.
I would tend to think that in a large industrial complex like a hospital or
high-rise building that the distributed, and unavoidable, ground paths,
(i.e. the entire building including conduits, building steel, concrete,
water pipes, etc.) is almost guaranteed to pose a much lower impedance fault
current path than can a single equipment grounding conductor run alongside
the hot.
As a sidebar, many, if not most, emergency generator installations at
communication sites are not seperately-derived systems because the neutrals
*are* tied together at the transfer switch. However, in the instant case,
where it is unknown whether or not the "red" and "white" are on separate
systems, I agree that switching the neutral and hot is the only safe way to
go.
--- Jeff WN3A
