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. -- Somebody should have said: A democracy is two wolves and a lamb voting on what to have for dinner. Freedom under a constitutional republic is a well armed lamb contesting the vote. Requiescas in pace o email Ex turpi causa non oritur actio Eppure si rinfresca ICBM Targeting Information: http://tinyurl.com/4sqczs http://tinyurl.com/7tp8ml