Main Breaker throw

Just had an incident where my 12x12k rack apparently threw its main breaker.  Dimmers 1&2 @ 60, 3&4 @ 70   9&10@70 11&12@80.  Measured Current on phases not greater than 142a.   Room was warm (87f)  Breaker warm but not hot, input cams warm but not hot.  Rack has double neutral.   Fixtures (All 10ks) had been working for 3+ hours.

Question:

Is the main breaker magnetic (I think it is)?  Will an over temp situation cause the main to throw?

Seems to be an anomaly.   Hasn't happened before and we're in our 14th week on this show.

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