A new circuit breaker for aircraft electric system: 40¿125 amperes, 120 volts A-C or D-C

RECOGNITION of the need for better protection of aircraft electric systems is indicated by the increasing use of reverse current circuit breakers in d-c generator circuits. Improved protection, however, must be extended to the entire electrical system and not confined to the generating equipment. Protective equipment for low capacity circuits in 28-volt d-c systems has been available. There has been a lack of protective equipment, however, for similar and higher capacity circuits in both a-c and d-c 120-volt systems. A new circuit breaker with ratings up to 125 amperes, 115 volts, a-c or d-c, recently developed is described. The requirements for such a circuit breaker are: 1. Interrupting capacity, 5,000 amperes sea level to 50,000 feet. 2. Ultimate trip current, 138 per cent of rated current at 25 degrees centigrade. 3. Continuous current capacity, 115 per cent of rated current at 25 degrees centigrade. 4. Two hundred per cent current calibration, 10¿100 seconds at 25 degrees centigrade. 5. Ambient temperature range, ¿55 degrees centigrade to 71 degrees centigrade.