"Art Todesco" wrote in message
...
On 5/29/2012 7:54 AM, Mr.E wrote:
On Mon, 28 May 2012 22:49:06 -0500, Vic Smith
wrote:

Last night I was in the basement on the PC, and watching TV.
Wife was asleep upstairs. Not sure if the central A/C was running,
but most the lights in the house were off.
I had a new service put in the year after I moved in, to get 240
so I could put in a new furnace and central air.
200 amp service, I was told.
The main breaker at the top of the box has a "pair" of breaker
switches that move as one. Each says "100" on it.
The furnace/A/C breaker is also a pair, each having "30" on it.
The rest of the breakers are 15 or 20.
Anyway, there was a loud bang, and all power in the house went off.
Didn't see a flash or anything, but the breaker box was out of my line
of sight.
I thought at first it was a transformer that blew up, which has
happened before, but the weather was clear.
But that didn't seem right because it was too loud in the basement,
which doesn't let hardly any sound in from outside.
It woke up my wife too.
I grabbed a flashlight and went upstairs, and saw right away my
neighbors had power.
Thought I was screwed, and would have to get the power company and/or
an electrician in.
Went back downstairs and found the main breaker had tripped.
Flipped it back on and the lights went on.
Another breaker was tripped - either a 15 or 20 - that runs some
basement lights and the pedestal pump for the lift system.
Flipped that back on too.
It's been about 24 hours, and everything's been normal. A/C running,
pump running, lights working.
That bang was pretty loud, about like a 1 1/2" firecracker, but not as
sharp sounding. Sounded "electrical" of course, but that's easy to
say when the lights go out at the same time.
Wish I had a recording.
Any idea what the hell happened?

Not at all unusual for a main to come out when a branch has a low ohm
short. Many branch type breakers have a lag built in to allow motor
starts etc. and the high amp flow caused the main to trip before the
lag in the branch.
I would disconnect the sump pump, carefully inspect the wires and if
an arm/rod activated level switch take the cover off and inspect for
an arc.
Nothing found would suggest inspection of other visible items on the
same circuit, again with power off.
Agreed. I was once changing a lamp in a gas stove (so it was only 120
volt branch) and accidentally shorted the 120. It took out the 100 amp
main and not the branch! I think the AC compressor had something to with
helping the 100 amp main trip. In addition, if you have 100 stamped on
the 2 main breakers, it is 100 amp service, not 200 amp ... well, the
service may be 200 amps, but you are only set up for 100 amps.

The above makes sense to me too. A branch circuit trip with just the right
transients and loads can trip the main breaker as well.

The good news is that your breakers are doing their job.

My rule is to endure one nuisance trip as a fluke. If it happens again,
more sleuthing is required.

Tomsic