Kirk,
insulation breakedon in older wiring like knob and tube, etc
Are AFCIs listed for use on circuits that do not include an EGC? It in my understanding that with the currently available AFCIs that the ground fault protection part of the device is the part that most often opens the circuit for high resistance or "glowing" faults. If there is not an EGC in the circuit, then the glowing fault would have to progress to a line to line fault before the AFCI would open the circuit.
Don
