[133039] in North American Network Operators' Group
RE: Want to move to all 208V for server racks
daemon@ATHENA.MIT.EDU (Alex Rubenstein)
Fri Dec 3 13:23:10 2010
From: Alex Rubenstein <alex@corp.nac.net>
To: "NANOG (nanog@nanog.org)" <nanog@nanog.org>
Date: Fri, 3 Dec 2010 13:22:47 -0500
In-Reply-To: <AANLkTimYN49oKgpseB41K_i9zJwYyNSsTnonyNdUy1WJ@mail.gmail.com>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
> > GFCI breakers are often required on large services, most large (new)
> > 480v services I have seen (1000A and larger) a have Ground fault
> > breakers,
>=20
> Actually, my recollection is that large new services include arc suppress=
ion
> rather than ground fault (480V service may be floating in any case, since=
it
> would depend on delta-wye distribution). There has been strong efforts t=
o
> protect the low voltage electricians (in common power distribution speak,
> 12K+ voltage is high voltage, less is considered low voltage; yes, this i=
s a
> different point of view). Even with a 100Cal suit on, you really want ar=
c
> suppression at those high joule ratings to protect a life (every master
> electrician has a story about arc flashes, and some stories include the o=
utline
> of the ex-individual on the opposite wall). It is now common when doing
> work on downstream devices to reduce the arc limits so that ones life has
> increased protection. A protective trip is better than the alternative.
Don't confused arc-flash protection with arc-flash circuit breakers. Doesn'=
t sound like you did, but I said it anyway.
As far as ground fault protection, in the 2008 NEC Code, it is required on =
any service 600 volts or less, 1000 amps or more, per 230.95.
As an aside, generally it is accepted that 600v and less is 'low voltage' (=
not to be confused with telecom/datcomm low voltage); 1kv to about 35kv or =
so is medium voltage, and above that is high voltage. I think IEEE or ANSI =
or someone defines this. Google around.
Arc flash is a whole new requirement, generally for the life safety aspect =
of the operators of the electrical equipment. I love putting on a arc flash=
suit to close a 800 amp breaker, when in the old days we'd do it barefoote=
d on a damp floor. Maybe it wasn't smart, but some of the new arc flash stu=
ff is a bit ridiculous.
