Code Q&A

Q. Will the AFCI breaker respond when a bedroom appliance has a locked-rotor condition, such as a window air conditioner? A. No and yes. The waveform signature of locked rotor current is not typical of an arc fault, so the AFCI will not respond. Under locked-rotor conditions, either the magnetic function or in time the thermal trip element of the protection device should open the circuit. Several
March 1, 2002

Q. Will the AFCI breaker respond when a bedroom appliance has a locked-rotor condition, such as a window air conditioner?

A. No and yes. The waveform signature of locked rotor current is not typical of an arc fault, so the AFCI will not respond. Under locked-rotor conditions, either the magnetic function or in time the thermal trip element of the protection device should open the circuit. Several small air-conditioning motors are equipped with a hermetically encased thermal limit device that will open before the branch circuit protection device. However, if the locked rotor current doesn’t open a protection device, the motor winding will ultimately short and the circuit breaker or fuse will open to safely clear the fault.


Q. Does a dedicated line for computer usage, marked “Computer Only” also need to be AFCI-protected? We install a separate line for computer equipment to have a stable, low-noise power supply.

A. Yes, if it’s in the bedroom.

About the Author

Mike Holt

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.

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