I have a treadmill, circular saw and vacuum that will trip the arc-fault. Did you run something motorized on this circuit?

In addition to the suggestions of what Hendricus says (hair dryers and other small motors are notorious for arcing internally), if this is a seven year old AFCI you're in the early generation of many of them. The GE ones for instance of that era (MOD2) are a pain in the butt. The current ones (MOD3) are much less likely to nuisance trip. You might try obtaining a more recent one on that circuit.

You can tell an AFCI as it will have a test button like a GFCI and should be labeled as such. If the AFCI is not the problem, then it's a job of sleuthing what device is operating when the breaker trips.

Number of reasons for tripping can be numerous. Better is to learn more about the tripping. Ie determine what must be on to cause tripping OR what, when powered on, causes that tripping.

If a motorized appliance causes 'nuisance' tripping, then the appliance has a defect. Some appliance power switches can be designed wrong to cause arcing. Or a needed snubber circuit was eliminated to 'save money'. No way around this. If any appliance causes 'nuisance' tripping, then a defect exists in that appliance.

One example of a trip is when the safety ground and neutral wire are shorted somewhere (ie inside the appliance or in wall receptacles). Simply separating safety ground from neutral wires can sometimes eliminate a 'nuisance' trip (that is actually detecting a defect).

Another example is a tool that connects a 33K half watt resistor or two 15K half watt resistors (in series) from the hot prong to earth ground (install them inside an AC plug to create a testing tool). The tool should cause no tripping. Then power other appliances. If those other appliances cause an arc or ground fault breaker to trip, then that appliance is leaking excessive current. The defective appliance is not leaking enough to always trip a breaker.

The least likely suspect is a defective breaker.

Again, I would disagree with westom's last statement, some of those early AFCIs are notoriously bad and just throwing a switch sometimes trips them (even with non-inductive loads).

I inspected all outlets and switches an didn't see any signs of shorts so I picked up a replacement Eaton 15a AFCI and noticed something that seemed odd when removing the old one.

The existing breaker had a small clip spanning the prongs that make contact to the panel. The replacement did not have this.

2 questions for the experts here:
1. What is this clip?
2. Should it be here and if not, is it possible this could have been contributing to the breaker tripping? Given all the warnings of making tight/secure contacts, I am wondering if this loose clip could have been part of the problem.

Thanks,
John

This post was edited by bantaj on Sat, Feb 1, 14 at 18:38

That is a spring to increase the clamping pressure on the bars in the panel. Quite valuable in my opinion. I do not know if the spring is discontinued on the new breakers, If so, the UL would have had to retest and list the changed unit.
It is possible that your sample inadvertently missed getting one, it was lost or the spring was pilfered. Perhaps you could inspect some other new samples. Could you install the spring you have on your new breaker?

If the new one did not come with a spring I would not sweat it. I see some with and some without. Many newer breakers without.