On 6/26/06, Tracy R Reed <[EMAIL PROTECTED]> wrote:
It is connected to an APC 3000XL. My understanding is that this is not
an "always-on-line" UPS. I think it runs off mains unless the mains fail
in which case it switches to batter.
An electrician should be showing up tomorrow. Hopefully I will find out
exactly what happened. Only one lead is burned...wouldn't that imply
that the power went to ground somewhere other than through that cable?
Nothing else is damaged anywhere so I am theorizing that something
shorted to the chassis of the UPS which went to the rack which went to
ground. But I am quite concerned because I'm pretty sure a circuit
breaker should have tripped somewhere long before that connector got fried.
Not necessarily -- the current in the connector could stay at 20A
while the effective contact resistance goes up from 0.01 ohm to 0.1
ohm, say. The voltage drop across the contact would increase from
0.2V to 2V which is insignificant compared to the 120V supply. But
the power dissipated in the contact would go from 4W to 40W. All
figures purely speculative except for the 20A and 120V.
They way I see the burned connector, it is in the ground lead. But
there is another positive feedback situation that can happen with
nearly-overloaded power connectors. The surface area in contact is
somehow less than it should be, thus causing more heat to be
generated, thus causing the contact area to decrease and generate more
heat. And so to meltdown. This was a common occurrence with some
versions of the internal power harness in a MicroVAX. I had it happen
with one out of two.
carl
--
carl lowenstein marine physical lab u.c. san diego
[EMAIL PROTECTED]
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