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

[Chuck Swiger]

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?  :-)