Section 440.22/Motor-Compressor Branch Circuit Short-Circuit Protection
NEC 440.22 establishes maximum overcurrent device ratings for motor-compressor branch circuits using the nameplate rated-load current (RLA) or branch-circuit selection current (BCSC), not FLC tables.
The branch-circuit short-circuit and ground-fault protective device for a single motor-compressor must not exceed 175% of the motor- compressor rated-load current (RLA) or branch-circuit selection current (BCSC), whichever is greater. If the calculated value does not correspond to a standard overcurrent device size, the next higher standard rating from Section 240.6 is permitted. If 175% is not sufficient for the starting current of the motor-compressor, the rating may be increased to 225% of the RLA or BCSC. The RLA and BCSC values are found on the equipment nameplate, not in the NEC FLC tables used for standard motors per Section 430.6. This distinction between Article 440 (motor-compressors) and Article 430 (general motors) is one of the most commonly confused aspects of motor circuit design.
Why this section exists
Hermetic refrigerant motor-compressors have different starting and running characteristics than standard induction motors. The sealed compressor design prevents direct measurement of motor current during manufacturing, so the nameplate RLA (rated-load amps) is determined by a standardized testing procedure rather than direct winding measurement. The BCSC (branch-circuit selection current) is a value set by the manufacturer that accounts for the starting current characteristics. Using FLC tables from Article 430 would not correctly represent the actual operating current of the sealed compressor motor.
What plan reviewers look for
Plan reviewers check the panel schedule for HVAC equipment circuits and verify the overcurrent device rating against 175% of the nameplate RLA or BCSC (not the FLC tables). They verify that the equipment nameplate data (RLA, BCSC, minimum circuit ampacity, and maximum overcurrent device size) is listed on the equipment schedule. They check that the conductor is sized per the minimum circuit ampacity from the equipment nameplate. For multi-motor equipment (rooftop units with compressor plus fan motors), they verify the combined circuit is sized per Section 440.35.