In some instances a short circuit will NOT trip the instantaneous trip of a circuit breaker. A case in point was a General Electric washing machine that was shorting out when reversing the motor to activate the spin action of the transmission. ( Motor forware = agitate and motor reverse = spin )

The culprit was a stuck contact in the part of the timer that acts as double pole doulbe throw reversing switch for the start winding of the motor. This short circuit only drew 120 amps of short circuit current which did not instantaneously trip a 20 amp General Electric circuit breaker. Made a really good buzzing noise until we either unplugged the washing machine or the overload element of the circuit breaker tripped out.

Considering that GE circuit breakers are almost as good as SquareD QO circuit breakers, this is a case in point where a "small" short circuit can heat up the wires more than a big short circuit. This also means that there is such a thing as a circuit that has too much impedance to trip a breaker or blow a fuse quickly.

Mike Cole mc5w at earthlink dot net

Mike,I think I located the error.Instead of the last para in the Newsletter,the following para may be the correct one. ''The effective ground fault current path is intended to facilitate the operation of the circuit overcurrent protective device in case of its low enough impedance or the ground-fault detector otherwise.''

Mike,Ofcourse,groundfault detectors are useful only for grounded systems.

Mike,When a ground fault occurs,the metal enclosure of faulted device rises almost to 120v/2=60v.A quick disconnection of power supply is needed.From the images provided here, it seems that by placing the panel near to the load,this could be achieved.But this is not true.Since the current return path is longer farther is the secondary of the utility distribution transformer,the effective ground return path may not be effective in some installations such that in case of fault, the overload device may not be fast enough to clear fault to prevent injury.