Perhaps un-sheilded Romex has a lower magnitude during signal propagation vs home runs in conduit, or cable armor.
Could be, but also remember that unshielded cable is more likely to be pierced by a nail or impacted by an over driven staple.
Magnetic trip curves are a function of time & energy, which usually trip well before overloads in most conditions.
Don't forget pickup values. There will always be point when cable length increases its impedance will increase to the point a dead short will not trigger the magnetic pickup. Available short circuit current is a function of the source impedance plus the conductors between the source and the fault.
Good question. A first outlet AFCI could only remove the load from arcs between the same wires, but not between different wires in home runs. The standard breaker magnetic trip and overload function would be tasked to deal with arc faults between different wires in home runs.
The overload function can be slower then 8 half cycles on a sputtering fault.
The breaker protects the home run against parallel arc faults, while the AFCI receptacle protects against parallel arc fault that may drop below 250amps as limited by the remaining circuit impedance (theorized to go as low as 75amps) and series arc faults 5 amps and over.
Perhaps not intended for several AFCI's to trip when only one is triggered, but not surprising when they are triggered by matching a wave form that can propagate from anywhere.
The look for certain ripples only, which is dumb because neither is the origin known nor what caused it.
It requires that the run by continuous, so no splices or j-boxes. Thus, without worry of loose connections the series arc fault risk is considered small and as such the breaker does not have to have that function.
