ground fault path

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Alb

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I decided to install a separate equipment grounding connector in EMT raceway and bond everything to it .In the event of a ground fault which path will the fault take? The EMT or the EGC. I understand that electricity seeks all available paths back to it?s source. Thanks for your help.
 
Alb said:
I decided to install a separate equipment grounding connector in EMT raceway and bond everything to it .In the event of a ground fault which path will the fault take? The EMT or the EGC. I understand that electricity seeks all available paths back to it?s source. Thanks for your help.
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You are right that the current will divide over all possible paths, taking it as a parallel circuit. The way the current divides will depend on the total resistance of each path.

If the wire and the raceway are not bonded at intermediate boxes, then if the wire resistance is .1 ohm and the raceway resistance is .2 ohm, the wire will carry twice as much current as the raceway.
If you bond at each box the EGC goes through, you have a more complicated problem if the ratio between wire impedance and raceway impedance is different for different segments for some reason. But the overall principle remains the same: the current will divide so that the voltage drop on both paths is equal.
 
The testing I have seen shows that the conduit is often the lower impedance path and there will be more fault current on the conduit than on the EGC. You can read some information from the Steel Tube Institute here
 
don_resqcapt19 said:
The testing I have seen shows that the conduit is often the lower impedance path and there will be more fault current on the conduit than on the EGC. You can read some information from the Steel Tube Institute here
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If the fault current originates from a wire which is not in the same conduit then magnetic induction will cause the current to flow preferentially in the conduit rather than the wire even if the DC resistance of the conduit is higher.

This effect will be most noticeable at high currents
 
Alb said:
I found some loose fittings, and some of them are not accessible for me to check.
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If you have loose fittings the chance of the raceway having the higher impedance goes up.

Also say you have this installation in a steel framed building, or there are other conductive paths present and are either intentionally or inadvertently connected to the EGC, those paths will also share some of the current.
 
GoldDigger said:
If the fault current originates from a wire which is not in the same conduit then magnetic induction will cause the current to flow preferentially in the conduit rather than the wire even if the DC resistance of the conduit is higher.

This effect will be most noticeable at high currents
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The testing was based on the supply to the fault being in the raceway that is carrying the fault current.
 
petersonra said:
I have to admit I have seen more than a few pieces of EMT that have come loose.
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Me too. More compression fittings than set screw, but I am of the opinion that it was a bad initial install that was the cause. Fittings do not just come loose by themselves.

In some cases vibration was the cause, but then again the original installer should have chosen a different method.
 
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