Re: floating a server room... how do you deal with ethernet connections?

Nikolas Britton wrote:
I'm currently planning renovations for the power mains supplying are
server room. One of the ideas I have is to float the entire room using
a isolation transformer.

Umph, that's normally only needed if you are seeing extreme line noise or have
other serious problems with the building mains supply like a poor or faulty
building ground. If you do have building grounding problems, then using an
isolation transformer will probably help your equipment but the problem should
still be fixed elsewhere.

The only problem to this solution, that I can
think of, is that all of the equipment that's attached to the other
end of the Ethernet cabling won't be isolated, the NIC cards do have
1:1 transformer coupling for the wire pairs but... In the event of
power surges, spikes, brownouts, and/or nearby lighting strikes I feel
that It's conceivable for there to be a large voltage differential on
the wires that could damage the equipment on ether end of the wire.

Actually, you don't even need a lightning strike-- one can see 50 to 100V swings
in relative voltages between neutral and the fusebox ground or neutral and a
water pipe just by having the building ground fail. [1] Adding an isolation
transformer to the mix won't hurt, but it won't help that much, either.

If you want room-wide surge suppression at the breaker panel, get a TVSS or a
10kVA or larger UPS. Consider something like the Leviton 54000 or 57000:

http://www.weberelectricsupply.com/57000.html
http://www.leviton.com/sections/prodinfo/newprod/npleadin.htm

...which are rated for 3-phase "wye" 120/208V or 277/408V @ 100 amps per phase,
and run about two grand. The other choice would be to hunt down a PowerWare or
maybe an APC Symmetra UPS, which will run 20-30K. Note that the APC Symmetra
cheats and doesn't provide galvanic isolation during normal operation, whereas
the PowerWare runs the inverter continuously which is a bit less efficient, but
gives cleaner power.

These sorts of units ought to have a "DC servo offset circuit", if I'm
remembering the details and phrase right, which will compensate for a constant
voltage differential between neutral and ground.

--
-Chuck

[1]: Three guesses as to how I know this? :-)
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