Re: POE switches and lightning

From: Larry Sheldon (no email)
Date: Fri May 14 2010 - 20:17:40 EDT

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    On 5/14/2010 19:00, Seth Mattinen wrote:
    > 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.

    In my experience, each building has a building ground-point at the
    service entrance, as outlined.

    I the problem in a campus on some soils is that building grounds might
    be several volts apart--except during thunder storms when the voltage
    difference might be (it appears) thousands of volts, and with a
    lightning strike to one of them many thousands of volts.

    That is why I argue for glass only between buildings. I don't care how
    much PoE saves.

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