well how about 12 ga on an AFCI breaker? wouldn't that 'help' find such a fault?
That will depend on who you are talking with as most don't believe that they work as claimed.
They seem to do fine with an arc between two conductors but no so good when the arc is contained in just one conductor. I have seen many discolored neutrals that were protected by arc fault and not tightened in the terminal bar and the arc fault did not open so should this be happening in a damaged cord it wouldn’t open either.
If it is not arcing and only overheating they will not open. Think of a portable electric heater, 1500 watts going through an 18 gauge cord for hours. The arc fault device is not seeing an arc but the cord is melting before your eyes.
Now think of a plug strip or a dollar store extension cord that has a high load. The arc fault will not protect against the heat generated by this load either.
Then we have the very delicate subject matter that is talked about in the circles that I sit in. Someone is doing work in their own homes or as most will call them the do-it-yourselfer that will not get inspections and has limited or no knowledge of what they are doing and seek help from other DIYers over the internet. In most of these cases the $65 arc fault is bypassed for the cheaper $6 standard breaker due simply to the cost. This is not to mention the other faults found such as box fill, types of joints, and the list go on and on.
Having worked with home inspectors during the sale of a home I have seen some pretty scary DIY installations and set in wonderment of how the home did not burn to the ground. One that comes to mind was a multiwire circuit from a two pole 30 amp breaker for the addition of a sunroom built over a patio. 12/3 was installed to supply the lights and receptacles and one receptacle at a window for a wall shaker. When the AC was turned on it tripped the 20 amp breaker so they replaced it with a 30.
The home inspector found one receptacle that didn’t work so he suggested me and the buyer had me take a look. This receptacle was cooked completely to the point of disintegration not to mention the damage to the cable.
I know this has little to do with the subject being discussed here but the heat allowed to pass through the 15 amp receptacles would have been the same should such a load have been protected by 20 amps.
My point is that a 15 amp receptacle is rated at 15 amps period. Yes the tab is rated at 20 amps let through but the receptacle (the part we plug into) is still rated for a load of no more than 12 amps so to install this on a 20 amp circuit will surly cause a failure on a heavily loaded receptacle.