Yesterday, the arc fault breaker on our master bedroom outlet circuit tripped and would not reset. Trying to isolate the problem, I eventually unplugged everything from the circuit. At that point the breaker reset and held, but as soon as I tried to draw any kind of load at all from the circuit, it tripped again. I figured it wasn't a short because the breaker always hesitated a few tenths of a second before it tripped.
Not really knowing where the problem could be or how to isolate it, I started pulling outlets out of the wall. I picked the one that I knew was the first thing on the circuit, and two others picked at random, and pulled them out. They looked OK. I disconnected the wiring at one, leaving a string of four outlets (out of a total of, I think, 11 on the circuit) still in the circuit. It still behaved the same -- the breaker tripped as soon as I drew any current from the circuit. I thought at one point that the first outlet might be faulty, even though there was nothing visibly wrong with it, so I bypassed it. Same result.
So I decided I was going to have to go through those four, one at a time. I un-wired the first outlet and rewired it so that that one outlet was the only one in the circuit. I plugged a table lamp into it, turned it on, and reset the breaker. It held. "OK, this is progress", I thought. Turned off the breaker again, and went back to the bedroom and pulled the second outlet in the string. This is an outlet where our bedroom TV is plugged in.
As soon as I had the outlet out of the wall, something caught my eye. There was a spot on the outlet's neutral terminal screw that was a different color. It looked like something had been rubbing on it. Pushing the outlet partway back into the wall, I noted that the ground wire was folded up and was coming up the side of the outlet. I pushed the ground wire up against the outlet, and sure enough, it fit onto the rubbed spot on the terminal screw. Hmm. I had been thinking about the possibility of a ground fault on the neutral side. I pulled the outlet back and and made sure the ground wire was well separated from the neutral terminal. Then I went back to the first outlet and restored that part of the circuit so that it fed the string again. Plugged in the lamp, turned on the breaker -- it held! As an experiment, I grabbed a length of wire, went back to the suspect outlet. I touched one end to the neutral screw and the other end to the ground wire. After touching in various places for about half a minute, I got the breaker to trip.
After putting everything back, making darn sure no ground wires were touching the neutral, I turned the circuit back on. Success! Everything worked. Interesting experience. I figured what happened is: The circuit is a long way from the service entrance; it's at the opposite end of the house and is fed from a subpanel. Evidently, the neutral floats above ground a few volts when there is a load in the circuit. If it touches the ground wire just right, the ground can divert enough current that the breaker senses a current difference.
Not really knowing where the problem could be or how to isolate it, I started pulling outlets out of the wall. I picked the one that I knew was the first thing on the circuit, and two others picked at random, and pulled them out. They looked OK. I disconnected the wiring at one, leaving a string of four outlets (out of a total of, I think, 11 on the circuit) still in the circuit. It still behaved the same -- the breaker tripped as soon as I drew any current from the circuit. I thought at one point that the first outlet might be faulty, even though there was nothing visibly wrong with it, so I bypassed it. Same result.
So I decided I was going to have to go through those four, one at a time. I un-wired the first outlet and rewired it so that that one outlet was the only one in the circuit. I plugged a table lamp into it, turned it on, and reset the breaker. It held. "OK, this is progress", I thought. Turned off the breaker again, and went back to the bedroom and pulled the second outlet in the string. This is an outlet where our bedroom TV is plugged in.
As soon as I had the outlet out of the wall, something caught my eye. There was a spot on the outlet's neutral terminal screw that was a different color. It looked like something had been rubbing on it. Pushing the outlet partway back into the wall, I noted that the ground wire was folded up and was coming up the side of the outlet. I pushed the ground wire up against the outlet, and sure enough, it fit onto the rubbed spot on the terminal screw. Hmm. I had been thinking about the possibility of a ground fault on the neutral side. I pulled the outlet back and and made sure the ground wire was well separated from the neutral terminal. Then I went back to the first outlet and restored that part of the circuit so that it fed the string again. Plugged in the lamp, turned on the breaker -- it held! As an experiment, I grabbed a length of wire, went back to the suspect outlet. I touched one end to the neutral screw and the other end to the ground wire. After touching in various places for about half a minute, I got the breaker to trip.
After putting everything back, making darn sure no ground wires were touching the neutral, I turned the circuit back on. Success! Everything worked. Interesting experience. I figured what happened is: The circuit is a long way from the service entrance; it's at the opposite end of the house and is fed from a subpanel. Evidently, the neutral floats above ground a few volts when there is a load in the circuit. If it touches the ground wire just right, the ground can divert enough current that the breaker senses a current difference.
