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3-phase bleedover (was Re: Summary: Bay Area Power (2000-06-14))
From: Bennett Todd <bet () rahul net>
Date: Fri, 16 Jun 2000 16:56:28 -0400

Hash: SHA1

2000-06-16-15:40:11 John Hall:
When you lose a part of a multi-phase circuit, you usually get
bleed through enduser devices that are still getting power through
the other phases.

Your story is a lot flashier than mine, but I had a really memorable
experience with 3-phase bleedover myself, once upon a time. I was
working at a research lab in the Duke Medical Center, in a small
building they called the Old Laundry Building, because it was. It
had a really ancient and heavy-duty building power distribution
panel; it had several 3-phase circuits running various big items;
and it had of course loads of regular power circuits. Including our
machine room.

Well, the building power panel breaker for the leg that carried our
machine room died. Actually I think it might have been a gigantic
fuse that blew, it's been so long I don't remember. Anyway, our
machine room was suddenly being powered by bleedthrough. Turns out
those 3-phase-powered appliances had a pretty darned significant
impedance, so our voltage available was suddenly remarkably
sensitive to how much load we applied to it. Unload the circuits and
the available voltage rose right up to about nominal, comfortably
over 110VAC or so; load everything on and the voltage dropped down
to something way way too low, like 40-50VAC or some such, again the
details are lost to me, I'm sorry.

Well, much of our machine room load was things like big SMD drives
- --- Fujitsu Eagles, Hitachi DK-815s, and the like. Weighed a ton,
drank power, and had sufficiently smart power supplies to take
themselves offline and spin down when the power dropped too far. At
which point the available power climbed up again, and they came on
again. They were cycling up and down every minute or so until we
managed to shut everything off. I think we only lost a couple of
power supplies and one HDA, if I recall correctly. Gear sure was
tougher then. Today I'd expect that kind of silly-buggers games to
let the magic smoke out of every box in a machine room, with the
possible rare exception of something indestructable like a 2511, too
mean to die. And of course laptops, which ties in nicely to another
thread I've committed hereabouts:-).

- -Bennett
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