On Fri, Dec 3, 2010 at 04:02, John van Oppen <jvanoppen@spectrumnet.us> wrote: ...
GFCI breakers are often required on large services, most large (new) 480v services I have seen (1000A and larger) a have Ground fault breakers,
Actually, my recollection is that large new services include arc suppression 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 to protect the low voltage electricians (in common power distribution speak, 12K+ voltage is high voltage, less is considered low voltage; yes, this is a different point of view). Even with a 100Cal suit on, you really want arc suppression at those high joule ratings to protect a life (every master electrician has a story about arc flashes, and some stories include the outline 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.
in fact I have seen some bad outages on entire datacenters where the main breakers had a lower ground-fault current setting (for tripping) than a branch circuit that had a phase-to-ground fault resulting in the main breakers tripping instead of the branch circuit.
*Proper* engineering is more than just putting in a breaker with a high enough rating. The days of nice resistive (think incandescent light bulbs) or inductive (motor/transformer) loads are long gone. Switching power supplies (or large pulse rectifiers) require a more careful analysis. I have seen too many upstream breakers being set at the wrong trip values (the larger breakers have internal adjustments), and trip first. Gary