Code Q&A: Using Circuit Breakers as a Switch

April 18, 2013

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.

About the Author

Mike Holt

Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.