Main breaker trip troubleshooting

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Systems

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Hi I was called to an apartment that have a 150 Amp panel (no main breaker) and a 150 Amp breaker by the meter stack. 2 days ago they lost power for about a minute, power came back and after few more minutes main breaker tripped. Today they had the same story again (maybe lost power twice before main breaker tripped). So, if there is a short on one of the circuits why the individual breakers (15, 20 etc.) didn't trip?, and if there is a short why did they lost power for a minute, got it back and lost again? I thought maybe one of the CB is bad and it doesn't trip which will cause the main the trip instead, so i intentionally shorted 4 breakers (2 were brand new - never used) to see what happens, the 20 Amp AND the 150 tripped every time i made the short. there are some marks on the meter lugs like it was hit by maybe lightning, or previous tenants trying to override the meter ? Can any one shad some light? Thank you
 
Sure the stabs at the main breaker aren't corroded/burnt or the connection of feeders causing loss of power and also creating high temperatures induced to main breaker therefore tripping it?
As for tripping both branch circuit breaker and main may be because the short circuit you created fell within the trip curves of both breakers.
 
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Systems said:
Hi I was called to an apartment that have a 150 Amp panel (no main breaker) and a 150 Amp breaker by the meter stack. 2 days ago they lost power for about a minute, power came back and after few more minutes main breaker tripped. Today they had the same story again (maybe lost power twice before main breaker tripped). So, if there is a short on one of the circuits why the individual breakers (15, 20 etc.) didn't trip?, and if there is a short why did they lost power for a minute, got it back and lost again? I thought maybe one of the CB is bad and it doesn't trip which will cause the main the trip instead, so i intentionally shorted 4 breakers (2 were brand new - never used) to see what happens, the 20 Amp AND the 150 tripped every time i made the short. there are some marks on the meter lugs like it was hit by maybe lightning, or previous tenants trying to override the meter ? Can any one shad some light? Thank you
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Sounds more like overload maybe by in-rush from A/C units all coming on at once, or bad connection causing tripping due to high temperature.

As far as "shed some light", you may shed more than light if you keep shorting breakers to trip them, BAD IDEA!:happyyes:
 
The breaker seems fine.

The breaker seems fine.

mopowr steve said:
Sure the stabs at the main breaker aren't corroded/burnt or the connection of feeders causing loss of power and also creating high temperatures induced to main breaker therefore tripping it? As for tripping both branch circuit breaker and main may be because the short circuit you created fell within the trip curves of both breakers.
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I guess im still young and stupid..:) they are all in trash.. right after i tested

I guess im still young and stupid..:) they are all in trash.. right after i tested

ptonsparky said:
Back when I was young & stupid we would play "trip the breaker" to ID the circuit we were working on. Occasionally we ran across one that would not trip. Be thankful both of yours did. Oh, you should probably discard those breakers you tested.
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All connections are tight

All connections are tight

Little Bill said:
Sounds more like overload maybe by in-rush from A/C units all coming on at once, or bad connection causing tripping due to high temperature. As far as "shed some light", you may shed more than light if you keep shorting breakers to trip them, BAD IDEA!:happyyes:
Click to expand...
One heat pump which seems fine Thank you:)
 
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