400A breaker heating up and tripping

[GoldDigger]

The only thing that I can blue sky as a cause of heating which would not show up on a power analyzer would be spikes or high frequency components which are for some reason not being counted by the power analyzer. But if the analyzer is designed to detect transients and spikes, and has a decent frequency response, that seems highly unlikely.
The other guess is that the power analyzer was not in fact recording any time that the breaker tripped. Which says that something intermittent, but long duration is involved.
Complicated by the possibility that a fault on a single motor can only cause a trip if there is additional load in parallel!

 

[Jraef]

Any chance that you are using extra flexible (high strand count) conductors, such as DLO / RHH/RHW? Most breaker lugs are not rated for high strand count conductors, so no matter how tight you get them, there is always a heating problem, usually leading to failure.

 

[GoldDigger]

Any chance that you are using extra flexible (high strand count) conductors, such as DLO / RHH/RHW? Most breaker lugs are not rated for high strand count conductors, so no matter how tight you get them, there is always a heating problem, usually leading to failure.

Looking at it another way, when you kept swapping breakers and positions to test, did you continue to use the same (or similar) conductors?

 

[A1b5c0pe1984]

Any chance that you are using extra flexible (high strand count) conductors, such as DLO / RHH/RHW? Most breaker lugs are not rated for high strand count conductors, so no matter how tight you get them, there is always a heating problem, usually leading to failure.

No, just copper 500s.

 

[A1b5c0pe1984]

Looking at it another way, when you kept swapping breakers and positions to test, did you continue to use the same (or similar) conductors?

Yes, the same wires are used. But they have been tested and are good.

 

[A1b5c0pe1984]

Update. We had the power company monitor their end of it to essentially cross it off the list of potential problems. I didn't think it was the problem, but like I said we're grasping at straws. Their end seems good, they were able to show the voltage when we had our breaker event, and showed other events where they thought there might be some disturbance on the line. I have bought a different breaker since I last posted, but it has not come in yet. Also we're down to 4 potential problem motor starter circuits. So the next time it trips will be the last time we have to trouble shoot the problem. Just want to say thanks for all of the input and ideas. I really appreciate it.