http://www.bussmann.com/tech/S_circuit.html I assumed a 1000 amps available at the breaker, 120 volt single phase circuit, and 100' of wire to the fault.
I had suggested 20' for the reason that the longer runs do act significantly to reduce the SCA.
The fault currents at 100' are:
#12 270amps, #10 370 amps, #8 425amps, #6 538amps, and #4 647amps.
I am not sure that this is the sole criterion.
I want to know in the case of a 20 A CB how many joules could be delivered before the breaker opens. My intuition tells me that the CB will open sooner with the higher fault current.I mean let's suppose that the SCA was 30 A because the run was 2000'. I would not consider this safer.
