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Circuit breaker random tripping?

77cruiser

Veteran Member
Senior Member
Bad breaker? 100 amp main service on my off peak electric. I think 3 times in about 1 week, never tripped before.
I had a 40 amp breaker on the electric heat, randomly tripped, finally changed it.
I have breaker in my shop that are used as light switches for 45 years & no problem with them.
 
I had an A/C unit tripped breaker once a week for a year. The whole A/C system was replaced due to rust. New system tripped breaker. I replaced the breaker, never tripped again.
 
Breaker are only supposed to be loaded to 80% of their amp rating, so a 100 amp breaker should only have an 80 amp load on it. If the feed wires are big enough, I would just upgrade it to s 125 amp unit if possible. This will require the feeders to be at least #2 awg if in conduit - bigger if it is fed by a romex like cable. This is presuming that your feeders are rated for 90° C. If they are rated for 75° C, then you will need feeders that are #1 awg or larger.
 
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Breakers work in two ways. The "fast" way (immediate trip) is electromechanical, that is a coil that becomes energized and trips the switch mechanism off. The magnetic core has a liquid damper that limits the time it takes for the trip to occur (like a shock absorber). If the oil leaks out the breaker will trip very easily.
The second way they will trip is thermal. If you have a heavy (high current) load a bimetallic element will heat up, expand, and trip the breaker.
Most likely it is the first, electromechanical trip that is the problem.
Replace the breaker. This would be the empirical method.
The analytical method would be to place an amp clamp on the wire feeding the breaker and record peak current levels, compare these readings to the manufacturer trip curve and see if the breaker is meeting specs.
If not meeting specs replace breaker.
If it is meeting specs then one or more of the loads the breaker is feeding has a problem e.g. a motor with sorted turns in it's wi.dings or a failed start capacitor.
 
I'd replace the breaker as when mine start to do that, after I replace them It never does it again. Too much current can cause hell on stuff.
 
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