Don,
The 1/4 cycle withstand for #14 is 3370 amps. That is below the AIC rating of all breakers.
It may have to do with the dynamic impedance of the protective device.
Regardless, during a test UL requires 10" (I was mistaken in my previous statment of 4') of rated conductor to be subjected to the same fault current as the breaker. This is to prove that the breaker protects the conductor.
This is a quote from a George Gregory article:
Every time a circuit breaker is tested under consistent circumstances, it demonstrates that the circuit breaker design will protect from the following:
• lateral forces that tend to break circuit breaker cases;
• in-line forces that tend to pull wires out of connectors;
• heating that tends to melt insulation.
