Increasing grounding size

[Martha Rosenow]

I have a 3 ph 208v 200amps service feeding a panel with 4#4/0 and 1#6 copper from a meter center. The inspector is requiring to enlarge the ground to a #4.The calculated load is 170.5 amps. The lenght of the feeder is 230 feet, no voltage drop issue here, it could go 330 feet without passing the 3% maximun voltage drop permitted. Should this grounding be changed to #4?

 

[charlie b]

The inspector is right. If I understand your question correctly, you have a 200 amp overcurrent device, then a set of 4/0 conductors, then a panel rated at 200 amps (for which the calculated load is not relevant). The ground wire is normally sized on the basis of the OCPD. For a 200 amp OCPD, you normally would need a #6 ground. But for a 200 amp feeder, you could have used a #3/0 conductors. You chose instead to use a larger wire. That brings article 250.122(B) into play, and you need to upsize the EGC.

Welcome to the forum. Sorry not to be able to give you happy news on your first question.

 

[augie47]

What if the larger conductor was used simply because the contractor has it "on hand" and didn't need to use it due to voltage drop ?

 

[raider1]

What if the larger conductor was used simply because the contractor has it "on hand" and didn't need to use it due to voltage drop ?

The CMP changed the heading of 250.122(B) from "Adjustment for voltage drop" from the 1999 NEC to "Increase in size" for the 2002 NEC code.

IMHO that means that for any reason if you increase the size of the ungrounded conductor you must also proportionally increase the EGC.

Chris

 

[LarryFine]

What if the larger conductor was used simply because the contractor has it "on hand" and didn't need to use it due to voltage drop ?

Even then.

I believe it's required in case anyone ever decides to use the oversized conductors at their ampacity.

 

[augie47]

The CMP changed the heading of 250.122(B) from "Adjustment for voltage drop" from the 1999 NEC to "Increase in size" for the 2002 NEC code.

IMHO that means that for any reason if you increase the size of the ungrounded conductor you must also proportionally increase the EGC.

Chris

Interesting change that slipped by me. Thanks

 

[augie47]

I have a 3 ph 208v 200amps service feeding a panel with 4#4/0 and 1#6 copper from a meter center. The inspector is requiring to enlarge the ground to a #4.The calculated load is 170.5 amps. The lenght of the feeder is 230 feet, no voltage drop issue here, it could go 330 feet without passing the 3% maximun voltage drop permitted. Should this grounding be changed to #4?

What type conduit system ?

 

[infinity]

What type conduit system ?

Are you asking in case it's a metallic raceway and he could therefore remove the #6?

 

[augie47]

indifference to my profession :grin:, yes

 

[fishin' electrician]

I believe it was don resqcapt19 that pointed this out.

Based on the literal wording of the text in 250.122, the conduit, tubing, et al would also need to be increased in size.

Notice in (A) they specifically mention EGC's "of the wire type", yet in (B) they do not. Oversight, maybe, but can't install/inspect to that. Or can we?

 

[chris kennedy]

What if the larger conductor was used simply because the contractor has it "on hand" and didn't need to use it due to voltage drop ?

Here is a fly in the ointment.

250.122 Size of Equipment Grounding Conductors.

(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.

The way the above reads leads one to believe that if the ungrounded conductors are upsized simply because thats what I have at the shop or on the truck then the EGC needs to be upsized also. Thats how I read it and install it.

Now here is the non enforceable commentary from the 08 NECHB.

Equipment grounding conductors on the load side of the service disconnecting means and overcurrent devices are sized based on the size of the feeder or branch-circuit overcurrent devices ahead of them. Where the ungrounded circuit conductors are increased in size to compensate for voltage drop or for any other reason related to proper circuit operation, the equipment grounding conductors must be increased proportionately.

Interesting interpretation.

 

[ActionDave]

Even then.

I believe it's required in case anyone ever decides to use the oversized conductors at their ampacity.

How is this so since following the rule can result in decreasing the EGC when using a larger breaker, eg. #6 @50A vs. #6 @20A?

 

[Dennis Alwon]

How is this so since following the rule can result in decreasing the EGC when using a larger breaker, eg. #6 @50A vs. #6 @20A?

Not sure what you are getting at but are you aware of art. 250.122(B)?

 

[charlie b]

I think what Dave is saying is that if you use #6 wire in a 20 amp branch circuit (i.e., 20 amp breaker), then you have to increase the EGC to #6. But if you later replace the 20 amp breaker with a 50 amp breaker, then you no longer need the #6 EGC, and you can (if you wanted) pull it out and replace it with a #10.

This entire topic just never made sense to me. I vote we ban 250.122(B).

 

[infinity]

This entire topic just never made sense to me. I vote we ban 250.122(B).

Well, if we can't ban the enitre section can we at least add an exception for when a metallic raceway is used that the supplemental EGC does not need to follow 250.122(B). :roll:

 

[ActionDave]

I think what Dave is saying is that if you use #6 wire in a 20 amp branch circuit (i.e., 20 amp breaker), then you have to increase the EGC to #6. But if you later replace the 20 amp breaker with a 50 amp breaker, then you no longer need the #6 EGC, and you can (if you wanted) pull it out and replace it with a #10.

This entire topic just never made sense to me. I vote we ban 250.122(B).

Yes, this is what I meant. Thank you Charlie. Your articulation and font are both superior to mine.