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Fuse and Circuit Breaker Sizing
The following information applies to compressor motor branch circuit, short circuit and ground
fault protection only.
NEC Article 440
Hermetic compressors should be protected in accordance with Article 440 of the National
Electric Code which calls for substantially larger circuit breakers than are required for open
type motors.
Maximum Size
The maximum size of the fuse or circuit breaker used to protect against short circuit and/
or ground fault of a unit utilizing a hermetic compressor shall be nomorethan the sum of
225% of the compressor Rated Load Amps (RLA) as marked on the system serial label,
plus the RLA values of each of the other motors which use the same branch circuit.
Minimum Size
The minimum value of the fuse or circuit breaker shall be nolessthan 175% of the RLA
of the compressor. The interpretations and directions given above apply only to single
branch power supplies and do NOT pertain to any plug-in type of appliances. Also, see
“PSC Motor Starting” on pages 17-18.
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