What is the use of the neutral in circuit breaker?

The heading of your question states " neutral in oil field", what does that mean?

Please describe the circuit breaker or give the make and model number of the breaker.

There are several reasons a neutral wire will be in a circuit breaker, depends on the breaker.

GFI's have a neutral, also Arc Fault are 2
TK, still trying to decypher oil field.