Thought some of you might add to this/
Came home from work 5:30 PM Monday,no power.
Found 100 amp breaker tripped re-set all OK
Same thing Tues.
Same thing Wed. after checking lines etc and again taking whole house
amps (Max38w/ air on and fridge on.
On way back up I was resetting clocks when I noticed they all stopped at the
same time.After checking my setback thermostat sure as hell main tripped at
program change.Went to held temp. problem solved. Still a little miffed that
30 amp air breaker held and 100 amp opened.
It will happen. I assume the 30 amp was for your AC condensing unit?
At a office building we had a 1000 amp, (yes one thousand!), main breaker
trip instead of a 40 amp for a AC unit. The compressor was shorted to
ground. The 40 was a time delay breaker of some sort, and the main was not.
Both breakers saw the short to ground, but the main was designed to trip
faster, so it did.
You should have an electrician come over and check the integrity of the
breaker connections to the 'buss'
If the 30 amp is loose it could cause heat to travel up the buss bar and
trip the 100 amp.
I would guess that your setback
thermostat somehow turned off the running
AC compressor and immediately turned it
back on at the time you indicated.
Depending on the AC condensing unit,
there may not be electronics
to prevent this. I have seen a small
short on a 15 amp branch circuit cause
the running AC compressor to stall and
take out the 100 amp main without
tripping the 15 amp circuit with the
short or the 40 amp AC breaker.
Apparently, the current from the short
circuit and the overcurrent from the
stalling compressor added up and took
out the main. I know on my setback
thermostats, there is supposed to be
built in time delays that prevent doing
unfriendly things to the compressor.
Apparently you found the source of the problem if I
read it right?
It's possible the reason the 30A didn't open but the
100A did was, because the 30A is a time-delay breaker?
The 100A, not being time delay, could open before the
30A in that case. In which case, it did its job.
Is it possible the 30A breaker was welded closed by the
short? Very, very unusual, but possible. If so, you
wouldn't be able to turn the breaker off and then back
on or if you were able to, it may not turn back on.
So if the 30A isn't a time-delayed breaker, I think I'd
check to be sure it's operational. It may not be able
Probably worth looking around where the short occurred
and at the panel to be sure no insulation melted, etc..
Any odors around that are new?
Just a couple thoughts; lots of possibilities, but
those come to mind first.
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