The testing of molded case circuit breakers with conductors

The authors clarify the rationale for testing circuit breakers under standard test conditions, with rated wire connected to the terminals. The role of molded case circuit breakers is to protect conductors and, in particular, insulated wires. For this reason, it is necessary to test circuit breakers with wires as a system to demonstrate that protection. The established tests for determining the interrupting rating of a circuit breaker are a practical representation of field installations of the products. The validity of standardized rating tests has been confirmed by accepted field performance. There is no evidence of problems with systems applications based on the marked ratings as determined by standardized test procedures. Similar short-circuit current tests with rated conductors for fusible disconnects and circuit breakers are done for all assembled products including panelboards, switchboards, motor control centers, and combination starters.<>