The circuit breaker in the open position is the time from the moment when the closing circuit is energized to the moment when all pole contacts are in contact. Unless otherwise stated, the closing time refers to the instant until the main contacts are in contact. The closing time refers to the time interval from the start of the closing command to the moment when the last pole arc contact contacts. In the previous relevant standards, the closing time is also called the inherent closing time.

The circuit breaker opening time refers to the time interval from the moment when the opening command is received to the moment when the arc contact heads of all poles are separated. The specific definition is as follows according to the different trip methods.

(1) For a circuit breaker that uses any form of auxiliary power trip, the opening time refers to the time from the moment the circuit breaker is in the closing position from the moment when the circuit breaker is energized with the opening release to the moment when the arc contacts of all poles are separated time interval.

(2) For a circuit breaker that uses the main circuit current without resorting to any form of auxiliary tripping, the opening time means that the circuit breaker in the closing position starts from the moment the main circuit current reaches the operating current of the current trip unit. The time interval between the moment the polar arc contacts separate.