Ground Conductor Sizing

[jphmeyers]

I have some equipment installed 2-3-400' from the subs and mains. It is wired with 2/0 copper to the equip. breakers and #4 copper ground. this is Delta wired equipment. I don't have my code book on site to reference this but I'm wandering if this ground conductor is big enough and, second would I be better to install a ground at each local equipment site since the distance is so great.

 

[Dennis Alwon]

Table 250.122 for the EGC is based on OCP size. I am guessing that your breaker is less than 300 amps or less, in which case a #4 is fine. 200 amps only needs #6

One thing you must be careful of is art. 250.122 (B). This usually comes into play based on upsizing for voltage drop.

art. 250.122(B) Increased in Size. Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately according to the circular mil area of the ungrounded conductors.

Here is a link to the 2005 NEC so you can check things from where you are at.

 

[petersonra]

I have some equipment installed 2-3-400' from the subs and mains. It is wired with 2/0 copper to the equip. breakers and #4 copper ground. this is Delta wired equipment. I don't have my code book on site to reference this but I'm wandering if this ground conductor is big enough and, second would I be better to install a ground at each local equipment site since the distance is so great.

Installing a ground at each location serves no purpose in clearing fault current, since the fault current is supposed to go back through the EGC and not the earth (in reality a small amount would, but not enough to make any real difference).

2/0 is good for less than 200A, so presumably the OCPD is a 200A breaker. That would make the minimum EGC a #6 per table 250.122. If it is run in conduit, the conduit would be an adequate ground by itself in all likelihood.

 

[Dennis Alwon]

2/0 is good for less than 200A, so presumably the OCPD is a 200A breaker. That would make the minimum EGC a #6 per table 250.122. If it is run in conduit, the conduit would be an adequate ground by itself in all likelihood.

This is true for the scenario you presented but suppose this equipment only needs a 60 amp breaker and the use of 2/0 was pulled for VD. #6-- 60 amp wire only needs a #10 EGC. If you upsize to 2/0 then that is 5 times larger than the #6 (cir. mill). Now you must upsize the EGC to 5 times greater than a #10 and you would need #3 minimum with rounding off otherwise you would need a #2 EGC. I believe rounding is allowed so I would say in the case I presented a #3 is required.

 

[augie47]

good explaination, Dennis

 

[Dennis Alwon]

good explaination, Dennis

Thank you. Occassionally I get something right.:grin:

That cursed me - now someone is going to find something wrong with the post--- oh no... :smile:

 

[petersonra]

<duplicate>

 

[petersonra]

This is true for the scenario you presented but suppose this equipment only needs a 60 amp breaker and the use of 2/0 was pulled for VD. #6-- 60 amp wire only needs a #10 EGC. If you upsize to 2/0 then that is 5 times larger than the #6 (cir. mill). Now you must upsize the EGC to 5 times greater than a #10 and you would need #3 minimum with rounding off otherwise you would need a #2 EGC. I believe rounding is allowed so I would say in the case I presented a #3 is required.

Good point. Perhaps the OP should clarify some.