600 amp main keeps tripping

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Benton

Benton

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Louisiana
I have a 600 amp main breaker that keeps tripping. The only load I have on it right now is a 150 amp three-phase breaker. The 150amp breaker doesn't trip but the 600 amp GE breaker keeps tripping. Any ideas of why this may be happening? It takes about five minutes before the breaker actually trips.
 
Benton said:
I have a 600 amp main breaker that keeps tripping. The only load I have on it right now is a 150 amp three-phase breaker. The 150amp breaker doesn't trip but the 600 amp GE breaker keeps tripping. Any ideas of why this may be happening? It takes about five minutes before the breaker actually trips.
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Have you measured the actual current on each phase?
Is the 600A breaker getting hot? There may be a bad connection (wire or bus) which is heating the breaker and making the thermal trip more sensitive.
An IR image of the breaker would be safer than a contact method of checking temperature, of course, since we have to assume that the line side of the main stays energized. :)
A constant close to full current load on the 150 combined with occasional spikes to a much higher current could be tripping the main instead of the 150 because of differences in the time-temperature curves of the two breakers.
 
Benton said:
I have a 600 amp main breaker that keeps tripping. The only load I have on it right now is a 150 amp three-phase breaker. The 150amp breaker doesn't trip but the 600 amp GE breaker keeps tripping. Any ideas of why this may be happening? It takes about five minutes before the breaker actually trips.
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What type of breaker is the 600A? Electronic trip unit? GFP? No way for us to know without better info. Really no way for anyone to know for sure without properly testing the 600A breaker.
 
Trip Unit? Injection Test?

Trip Unit? Injection Test?

The first thing I thought of is a faulty trip unit... if there is one.. Can you take the breaker out and inject current to see if it's the breaker?
I've run into a similar situation with a 1200A breaker tripping with zero load on the line. We just had to replace the breaker. Perhaps and IR scan would help indicate a problem...
If there is a trip unit, equipped with thermal memory, try disabling it.
 
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