Primary injection testing of a ground fault circuit breaker may cause the breaker to trip, not allowing testing to be completed. This is caused by the integral ground fault sensing capabilities in breakers with ground fault trip units. A solution is to use the "looping method" so that each pole of the breaker can be tested without tripping on ground fault.
Circuit Breakers with Ground Fault Trip Units
The looping method is used to allow primary injection testing of breakers with ground fault trip units. In this method, jumpers are added line and load to so that each pole may be tested separately. The below drawing shows looping when testing A phase. For B and C phases, move jumpers as necessary.