Code Q&A: Using Circuit Breakers as a Switch

Your most pressing National Electrical Code (NEC) questions answered

Q. What type of circuit breaker does the Code allow to be used for switching duty of lighting circuits?

A. Circuit breakers used to switch 120V or 277V fluorescent lighting circuits must be listed and marked SWD or HID. Circuit breakers used to switch high-intensity discharge lighting circuits must be listed and marked HID [240.83(D)]. Note: This rule applies only when the circuit breaker is used as the switch. If a general-use snap switch or contactor is used to control the lighting, this rule doesn't apply.

UL 489, Standard for Molded Case Circuit Breakers, permits "HID" breakers to be rated up to 50A, whereas an "SWD" breaker can only be rated up to 20A. The tests for "HID" breakers include an endurance test at 75% power factor, whereas "SWD" breakers are endurance-tested at 100% power factor. The contacts and the spring of an "HID" breaker are of a heavier-duty material to dissipate the increased heat caused by the increased current flow in the circuit, because the "HID" luminaire takes a minute or two to ignite the lamp.

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