Discovering the Root of the Problems: Troubleshooting GFCI- and AFCI-protected electrical circuits

stock.adobe.com / The Toidi / FreshIdea
stock.adobe.com / The Toidi / FreshIdea
Published On
Sep 15, 2021

When I was an electrical contractor, I specialized in high-end dwellings, medium-sized design-build commercial installations, and industrial facility maintenance and machinery. I had a small electrical service department of approximately six electricians doing troubleshooting and small electrical service work for customers. This work usually kept everyone fairly busy.

Only periodically did I get personally involved in the troubleshooting, and then only when something unusual made it difficult to determine the cause of the issue. Some of those difficulties dealt with troubleshooting GFCI circuits and AFCI circuit-breaker tripping issues, which can be much more challenging than GFCI ones.

Bathroom tripper

I responded to a call about a GFCI receptacle in a family home’s downstairs bathroom that would sometimes trip. No one could tell me when the trip would occur, just that it would randomly trip off. There were multiple circuits in the box, lighting and receptacle ones that supplied the GFCI receptacle. The receptacle was energized when I arrived.

I measured the trip value of the GFCI device using a leakage meter designed for this purpose to ensure there wasn’t something wrong with the GFCI device. It tested at a trip value of 5 milliamperes (mA), which was between the trip value of 4–6 mA set by UL and the manufacturer. I took all of the circuits apart within the box and could not find a problem with the circuit. I was at my wits’ end that I could not determine why it was periodically tripping.

Before I sat down at the dining room table to write up my findings, I turned the light on and heard the GFCI receptacle trip. Upon closer examination of the lighting switch box at the bathroom’s entrance, I found a circuit for the lighting in the dining room, kitchen and bathroom.

The load, or output side, of the GFCI receptacle went from the receptacle box to the switch box, and from there to another bathroom circuit in the same light switch box. The neutral for the dining room lighting circuit had inadvertently been connected to the load side of the neutral of the GFCI. This meant that any time the dining room light was turned on, the imbalance of the neutral current from the dining room light would trip the bathroom GFCI receptacle. If I hadn’t stopped to write up my report at the dining room table, I may not have found the problem.

Outdoor inductance

On another service call, I had a difficult time determining why GFCI receptacles were tripping periodically. A new housing subdivision was built in close proximity to a public easement with 500-kilovolt overhead utility company lines. Homeowners found that any GFCI receptacles located on the homes’ exteriors were inadvertently tripping for no apparent reason.

After a few hours of troubleshooting, I determined that high-voltage inductance was causing the GFCI receptacles to trip. I solved the problem by replacing the GFCI receptacles with GFCI breakers. The only conclusion that I could logically assume was that inductive current in the circuit caused an imbalance between the hot conductor and the neutral conductor on the load side of the GFCI receptacle.

Unlisted fans and home offices

A few years back, I received a rash of phone calls from electrical contractors about AFCI circuit breakers tripping with no apparent cause. The tripping issue was not limited to just one manufacturer. I determined there were two different issues: (1) the AFCI devices would trip when ceiling paddle fans with remote control functions were installed on the circuits, and (2) there were bedrooms converted to home offices with computers, printers and other small office equipment.

With the first issue, the ceiling paddle fans were almost all unlisted ones with remote control units. Invariably, the AFCI breakers would trip when the owner used the fan’s remote. I had the ECs replace the ceiling paddle fans with listed fans and the problem went away. The remote electronic control was causing an imbalance with functional current being routed to the equipment grounding conductor and not the neutral. I also found something similar with small office electronic equipment, where functional current was being routed to the equipment grounding conductor rather than the neutral.

Over the years, I have found that troubleshooting electrical circuits can sometimes confound experts, but there are usually basic issues involved with each circumstance.

About the Author

Mark C. Ode

Fire/Life Safety, Residential and Code Contributor

Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and Mark.C.Ode@ul.com.

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