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If a three-phase circuit breaker is specified as, for example, a 32 A breaker, does this mean the breaker will trip when the current in a single phase exceeds 32 A, or when the total current of all three phases combined exceed 32 A?

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If you are talking about general purpose 3 Phase breakers, they are 3 individual breakers mechanically coupled to ensure an overcurrent on any one phase will trip all 3.

If you have a 32A breaker, then the instantaneous trip current is far above 32A. The standards typically classify the trip point at 0.1 seconds. For current at the rating the trip time may never occur, or may occur in hundreds of hours (usually temperature sensitive).

This article will talk you through the trip characteristics. Typical residential applications use Class B or C breakers.

Class B breaks instantaneously (<0.1s) at 3-5 times rated current.

Class C breaks instantaneously (<0.1s) at 5-10 times rated current.

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A 32 amp three-phase breaker should effectively be three 32 amp breakers in one box. All three phases should operate together.

It should open all phases if the current in any phase exceeds 32 amps.

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