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Code Q&A

Mar 1, 2002 12:00 PM, By Mike Holt, NEC Consultant

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.