Troubleshooting AFCI breaker tripping

INTRODUCTION

AFCI breakers are so sensitive that I often hear of electrician complaints that they may be giving false alarms. However, I have installed more than 100 of them and only ever encountered one – maybe – that may have been tripping improperly. I’m not sure I could report as good a record for standard breakers, whose failure rate I’ve not monitored as closely (they cost 1/5 as much, for one thing).

Recently, I had the new experience of inadvertently using an AFCI breaker as a fake-grounded receptacle tester. Initially, I was chagrined to have to extend my work to troubleshooting a ‘perfectly functional’ circuit, but it turns out this was a dangerous circuit and the AFCI ‘fake-ground detector’ is a good tool to keep in the proverbial chest, and one more reason to use these breakers as much as possible, even on existing circuits, in spite of their expense.

 

THE FAULT CONDITION

After modifying an existing circuit, I was replacing the breaker serving it with an AFCI type breaker, per NEC 2008 in force in my area, and found that the breaker would not latch on due to some fault in the circuit.

 

TROUBLESHOOTING AFCI BREAKERS

Step 1: Narrow the field

Murray/Siemens AFCI’s may indicate the type of fault that tripped them, while other types simply indicate tripped, with no indication whether due to overload, or if from an arc fault condition, what type. For any breaker type, you can determine whether you are looking for a fault related to the phase (‘hot’) conductor, or the grounded conductor (‘neutral’), by removing all loads from the circuit and then disconnecting one conductor or the other from the breaker and trying it to latch on. If removing the neutral allows the AFCI to latch on, then you have a fault there. Vice versa for the hot.

Step 2: Go to a midway point

Begin at a midway point in the branch circuit served by the AFCI. Repeat the isolating steps from Step 1, above, to determine if the fault is on the line or load side of your mid-point. You can now work your way either back toward the breaker, or if there are still many locations between you and an end point in the circuit, pick a ‘quarter-way’ point and keep dividing your problem until you arrive at the fault.

In my case, I was unlucky enough that the fault was nearly at the farthest load end of the circuit, so I opened quite a number of locations before arriving at the problem. Fortunately, there were lazy ground bonding issues with almost every location, and some older receptacle devices needed replacing (with Tamper Resistant type, of course), anyway.

Step 3: Locating and clearing the fault condition

The problem turned out to be unnecessarily-fake-grounded receptacles with the neutral and equipment-grounding terminals bonded behind the receptacle device. Somebody in the building got happy with the black magic of neutral-ground bonding ‘fixing’ everything, so they did it at the fault location as well as behind a GFCI device on another circuit, in both cases where there was already a proper equipment grounding conductor! My AFCI fault location was an especially egregious example of this dangerous practice, since the receptacles are mounted on exposed metal raceway (Wiremold) that would have become energized any time the receptacles were in use. This raceway was running at shin-height: perfect for an infant to lick or suck on!

After properly bonding the equipment grounding wires with a wire nut (they were tightly twisted already, but the wire nut ensures true bonding), and removing the bonding jumper on the receptacles, between neutral and grounding terminals, I then tried the AFCI breaker again and found that it latched on.

 

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See also:

• AFCI’s, Cost & Fire Safety
• The Circuit Detective: AFCI Circuit Breaker Troubleshooting
• International Association of Electrical Inspectors (IAEI) article on GFCI and AFCI circuits
• Schneider Electric, Determining the Cause of AFCI Breaker Tripping

1 Comment

• AFCI’s, cost, and fire-safety « « Licensed Electrician Robert Monk Licensed Electrician Robert Monk 2012/04/14 at 11:45 PM

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