3 Feb
2011
3 Feb
'11
1:57 p.m.
On Wednesday, February 02, 2011, Tony Duell wrote:
Yes, I mean 200A.
Ouch. I how most of that is either for a short duration (switch-on
surges) on in quatrature to the supply so that no real power is being
consumed.
The
ground fault breaker (RCD by you) on the 480V supply the work's
main datacenter (which is rated at 1MVA, or 1200A currently - an
upgrade to 5MW is coming this year) was tripping on us when it was
set to 200-300A,
Dop you mean that? 200A (not mA) of earth leakage wouldappear to be
dangerously high in any installation.
When you're dealing with high-ish voltage (277V to ground), and lots of
power being used (about 1000 amps per phase), leakages can add up
Even so, it's high. It's around 1/15 of the total current, which, pro
rata would be a leakage of 1A on a medium-sizedd PDP11, say. If my PDP11
had that sort of leak, I would be repairing it. Period.
quickly... And, it's most likely a spike, not a
continuous leakage
current, eg, a short-lived arc to ground from some worn out insulating
parts.
That is precisely the sort of thing I would repair and not just turn up
the breakers to get round it! Worn-out isulation (whatever that may
mean) is not something I am going to trust.
In any case a 200A short-term fault isn't all that huge. Ratings for
typical US house circuit breakers are around 10,000A interrupting
capability.
That is surely the maximum fault current they will safely break. Not the
current they carry before they trip. Over here most decent domestic MCBs
will break 16kA safely -- that is the peak current that might flow if
there's a dead short across the mains. But said breakers will trip on a
current of 32A, say.
-tony