What would make an arc fault breaker trip on a bedroom circuit other than a ground and a neutral touching (which isn't the case - we checked all the switch boxes) or a pinched wire (staple pounded in too hard)?

We got one that trips the instant you flip on the light switch...checked all the outlets in the rooms for a loose connection and checked all the grounds and neutrals in the switch boxes...

just for the record - we didn't wire this house to begin with

The n-g touching will not trip an afci breaker. Has there been any new siding put on the outside of the house? Nails piercing the NM will do the trick.

ron,
It would trip it if it is a combination Afci/gfci breaker.

Happi,
Have you tried disconnecting the fixture to see if that is where the fault is?

Happi,

This may sound strange, but I have had this happen where the problem was an internally shorted Light Bulb. Try taking the Bulb(s) out of the fixture and see what happens. It's worth a shot.

Bill

Ron,
All AFCIs have built in ground fault protection at the 30 to 50 mA level and a neutral to ground short will cause them to trip.
Don

Happi_Man,

I had this same thing happen to me, also in a house that I did not wire from the beginning. It turned out that the neutral from the AFCI circuit was landed on the neutral bar in the panel, and the neutral from another circuit was landed on the AFCI breaker. Therefore, whenever a load was placed on the AFCI circuit, it sensed a ground fault and tripped. Lots of head scratching over that one until I finally double checked all of the wires in the panel.

Jim

Another problem would be if there is 2 separate feeds in the switch box , and all the neutrals are spliced together,would trip the afci also.