Effective Ground-Fault Current Path

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Twoskinsoneman

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
When installing a raceway as an EGC.Do you just assume it meets 250.122(A) and subsequently 250.4A)(5)? Or is there test that have to be done?

How do we know that our raceway is "capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source."??

Like if I have a 100 amp circuit I need a #8 CU EGC... Can I just assume that whatever raceway size is needed to meet fill can handle that amount of current to clear a fault???
 
I personally have never relied on the raceway to act as an EGC.........I have always pulled a wire for that. I know it is perfectly acceptable to do that but my personal preference is to have that "back-up". I would think the properly sized raceway will have larger surface area than any wire EGC. If you do it, make sure your fittings are tight.
 
Twoskinsoneman said:
Like if I have a 100 amp circuit I need a #8 CU EGC... Can I just assume that whatever raceway size is needed to meet fill can handle that amount of current to clear a fault???
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Yes, you can, and better than the #8, as long as you make joints up properly.
 
Twoskinsoneman said:
How is it allowed to assume it meets these requirements? How do we know it is going to carry the current to clear a fault?
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Go HERE, spend some time, and down load the software.

As far as testing the conduit, a simple ohm meter will work as well as it would for a testing wire.

Roger
 
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You cannot assume that either the raceway or the EGC sized per 250.122 is an effective fault clearing path. In most cases it will be, however it is possible, in cases where the available fault current is very high, for an EGC sized per 250.122 to not be an effective fault clearing path.
 
Don, as usual, there's an exception to every rule, but it's safe to say that a conduit that is sized for any given set of conductors has an ampacity of at least as great as the compliantly-sized EGC for those same condcutors.

Would you agree with this generalization?
 
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