This article was posted 12/15/2006 and is most likely outdated.

Article 250 Grounding and Bonding 250.2
 

 
Topic - Article 250 Grounding and Bonding 250.2

December 15, 2006  

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Grounding and Bonding

250.2 Definitions

Part I. General

Additional text helps the Code user understand that the purpose of the effective ground fault current path is to help clear a ground-fault by facilitating the operation of the overcurrent device.

Effective Ground-Fault Current Path. An intentionally constructed, permanent, low-impedance conductive path designed to carry fault current from the point of a ground fault on a wiring system to the grounded neutral point at the electrical supply source. Figure 250-1

The effective ground-fault current path is intended to facilitate the operation of the circuit overcurrent protective device, or the ground-fault detector on a high-impedance grounded system. Figure 250-2



Figure 250-1
(Click on image to enlarge)


Figure 250-2
(Click on image to enlarge)

     
 
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Comments

  • 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

    Michael R. Cole
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