Now that it's almost 2008, I'm giving serious consideration to installing several hundred AFCIs in the coming months. I had a thought that it might not be a code violation to tie the two ungrounded conductors of a MWBC (anywhere but on the breaker itself) and terminate it on one AFCI breaker. In my rather small home these two 15-amp circuits are 18 receptacles and lights, including a bath GFCI receptacle.

Dave

Tiger,
I think that goes against good wiring practice regarding placing the two ungrounded conductors on opposite sides of the phase so the neutral only carries the unbalanced portion of the load as opposed to the full neutral current of both ungrounded conductors.
You would probably be safer and more code compliant, depending on the actual load, if you just used one side of the MWBC to feed all of the receptacles and lighting as one two-wire circuit.

JMHO

I see from their literature that Siemens now makes a two-pole combination AFCI cb for this type of application.
This is what I will need to use for my second floor bedroom circuits when the time comes as they were also wired with 14/3.
There may be other manufacturers making two-pole combination AFCI cb’s, but not sure.