derating grounding conductor

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Bowhunter

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Is it necessary to derate the grounding conductors if I'm running two feeders for 3 phase 4-wire panels in the same raceway and they are passing through a 35 degree C area.
 
The equipment grounding conductors are not rated for ampacity anyway, so the concept of derating would not apply to them.
 
Thanks for your reply.

I thought that maybe because the equipment grounding conductor was sized according to the amperage of the overcurrent device in T250.122 at some point with derating it might call a larger wire than is shown in T250.122.

Thanks
 
Bowhunter said:
Thanks for your reply.

I thought that maybe because the equipment grounding conductor was sized according to the amperage of the overcurrent device in T250.122 at some point with derating it might call a larger wire than is shown in T250.122.

Thanks
Click to expand...

It's not considered a current-carrying conductor (CCC).
 
Let's be clear about our use of terminology here.
  • IF because of having more than three current-carrying conductors in the same raceway you have to derate the conductor's ampacity,
  • AND IF because of this you have to use a larger size wire for the ungrounded conductors,
  • THEN you also have to use a larger EGC.
But that is not a process of derating the EGC, since as I said already the EGC does not have an ampacity rating.
 
charlie b said:
Let's be clear about our use of terminology here.
  • IF because of having more than three current-carrying conductors in the same raceway you have to derate the conductor's ampacity,
  • AND IF because of this you have to use a larger size wire for the ungrounded conductors,
  • THEN you also have to use a larger EGC.
But that is not a process of derating the EGC, since as I said already the EGC does not have an ampacity rating.
Click to expand...

250.122(B), if anyone wants to look it up.
 
Sorry I took so long to get back.

I read 250.122(B) and I understand it to say if I have to increase the size of the ungrounded conductors because of derating or volt drop then I should increase the size of the equiptment grounding conductor proportionately. So its
got nothing to do with carrying current unless there is a fault.

Do you agree?
 
Bowhunter said:
Sorry I took so long to get back.

I read 250.122(B) and I understand it to say if I have to increase the size of the ungrounded conductors because of derating or volt drop then I should increase the size of the equiptment grounding conductor proportionately. So its
got nothing to do with carrying current unless there is a fault.

Do you agree?
Click to expand...


If you circuit conductors were so long that due to voltage drop you needed larger conductors then the same thing would apply to the EGC. It would need to be large enough (and it's resistance low enough) to ensure that it can quickly open the OCPD ahead of the circuit. As far a increasing the EGC size for derating there is no real world reason to do this but it is required because of 250.122(B).
 
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