[126427] in North American Network Operators' Group
Re: POE switches and lightning
daemon@ATHENA.MIT.EDU (Seth Mattinen)
Fri May 14 20:00:39 2010
Date: Fri, 14 May 2010 17:00:44 -0700
From: Seth Mattinen <sethm@rollernet.us>
To: nanog@nanog.org
In-Reply-To: <alpine.LFD.2.00.1005150135220.22843@filebunker.xip.at>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On 5/14/2010 16:42, Ingo Flaschberger wrote:
>>> We had a lightning strike nearby yesterday that looks to have come
>>> inside our facility via a feeder circuit that goes outdoors
>>> underground to our facility's gate.
>
> Perhaps there was a "move" of the earth-level relative to the neutral line.
> I have no idea how neutral-line to earth potential is handled in us, but
> here in austria we use a so called "nullung".
> That means that the earth-ground potential line of the building (which
> includes also the lightning conductor) is connected to the neutral power
> line where it enters the building, keeping this potential-difference low.
>
In the US neutral and earth ground are supposed to be bonded only once
at the service entrance. A separate ground from the neutral conductor is
carried to sub-panels where is it not bonded. Additional bonding can
cause weirdness and will turn the ground into a current carrying
conductor. However, an older building I used to be in (built 1978) only
gave me a neutral with bonded subs, so you'll run into all kinds of
stuff depending on the age of the building. Working at a university was
particularly interesting with of the vast range of building ages.
~Seth
