Your assumptions about the neutral/ ground interconnection are real possibilities. I would inspect the connections within the wall/ ceiling boxes on the affected circuit. It is possible that this problem existed prior to the foreclosure and the frustrated occupant broke the button on the AFCI. Or possible that the problem is sabotage by said occupant. And using a regular breaker for testing would definitely be in my bag of tricks.

What type AFCI breaker do you have?

Is this a standard type AFCI breaker or does it say "combination type" AFCI breaker?

Unless it is a "combination type" AFCI breaker, it will not sense neutral-to-ground faults...and combination type AFCI breakers were not required to be installed (and were not even available on the market) until January of 2008.

If the house was completed in 2007, it is likley you have an older standard AFCI which should not trip in the presence of a neutral to ground fault.

Also, it is hard to determine from your description above, but you seem to have indicated that the bathroom circuit is also protected by this AFCI breaker?

If so, this may be your problem because the bathroom is required by Code to be on its own 20 amp circuit, not tied into the bedroom AFCI protected circuit.

In other words, you should not have the bathroom GFCI device tied to an AFCI breaker.

Tripping only when something is plugged in means you have a neutral problem, possibly an improperly shared neutral between two circuits or an improperly installed breaker. Check the breaker installation first, making sure the pigtail from the breaker is attached to the neutral bus and the neutral for the circuit is attached to the AFCI breaker.

Sorry Manhattan, that is incorrect. The difference between the branch/feeder and the combination is the ability to detect series arcing. There is no difference in their ground fault handling.

"...pigtail from the breaker is attached to the neutral bus and the neutral for the circuit is attached to the AFCI breaker."

This is a common mistake for homeowner installed AFCI breakers, and GFCI ones also.

The branch circuit neutral MUST land on the breaker, NOT run directly to the neutral bar.

ronnatalie wrongly alleged:

"Sorry Manhattan, that is incorrect. The difference between the branch/feeder and the combination is the ability to detect series arcing. There is no difference in their ground fault handling."

I did not say what ronnatalie claims I did, and ronnatalie appears confused by this topic.

First, 'standard type' and 'combination type' arc fault circuit interrupters are both branch/feeder type breakers.

Second, 'standard type' AFCI breakers are unable to detect 'combination' type arcing faults. 'Standard type' AFCI breakers only detect 'series' type arcing-faults.

Only 'Combination' Type AFCI breakers (which were only introduced in January of 2008 after the house was built) can detect arcing-faults such as those that could occur between a neutral-and- ground.

The point is: Since it appears that kingmer has only a 'standard type' AFCI branch/feeder breaker, it is unable to detect an arcing-fault condition between neutral-and-ground and this type arcing-fault condition would not be the cause of the AFCI tripping.

That does not rule out however, the possibility of a 'dead short' condition or miswiring of the AFCI equipment (as others have already mentioned) which could indeed cause the breaker to trip under an overload, not an arc-fault condition.

Thirdly, my additional comments about the GFCIs addressed the likelihood that the bedroom and bathroom circuits may be completely miswired.

Why?

Because the NEC requires bathrooms to be wired on separate branch circuits from bedrooms, and the presence of GFCI receptacle equipment on an AFCI protected branch circuit may still be contributing to the problem.

If the 'electrician' miswired the bedroom and bathroom, it would not be surprising if he also miswired the AFCI breaker and other equipment on the circuit as well, and there could therefore be multiple violations with multiple contibuting factors to cause the AFCI branch/feeder device to 'trip'.

That said, ALL these possible violations would need to be examined and corrected to resolve the problem. There may be multiple causes for this tripping AFCI breaker, not just one.

You show me where in 1699 that it says anything about neutral to ground arcing? Now you are inserting crap that I never said. Yes, the combination AFCI is a branch-protecting device (just like any panel mounted breaker), but indeed the "COMBINATION" terminology comes from the fact that it engendered the protections provided in the original "branch/feeder" and "outlet" definitions.

As for the rest of the diagnostic things you mention, I agree 100%. There's almost certainly some miswiring, either something that was gotten away with before: either some inappropriate cross circuit connections (neutrals touching) or a ground fault (for example, someone installing one of the fancier neutral requiring dimmers using the ground for a missing neutral in the switch box), etc...

It's going to take some serious sleuthing (divide and conquer), but there probably is an existing legitimate problem with the wiring (or some real brain fart on hooking up the breaker in the panel, like the neutrals were connected to the wrong breaker).

From GE, courtesy of another forum:

1. Branch/Feeder AFCI

A Branch/Feeder AFCI has the ability to detect and neutralize a parallel arc fault, which is the unintentional flow of electricity between two separate wires. There are three types of parallel arc faults: line-to-line, line-to-ground, and line-to-neutral. The Branch/Feeder AFCI is permitted by the 1999-2005 NECî Code.

2.Combination AFCI

GE's Combination AFCI delivers 5 kinds of protection:

1. Parallel protection: Just like its Branch/Feeder counterpart, Combination AFCI can detect and neutralize parallel arc faults
2. Series Protection: A series arc fault is the unintended flow of electricity over a gap within a single wire. These arc faults were not detectable until advanced technology allowed the development of the Combination AFCI breaker.
3. Ground protection: Arcing between a single conductor and a ground line
4. Overload protection
5. Short circuit protection