NEC 250.30(3) Exception No 2

[Shujinko]

What does NEC 250.30(3) Exception 2 really mean? I have an inspector that suggested the grounding electrode conductor of the secondary side of a dry-type transformer be connected this way. But it's a bit unclear to me what is trying to be said in this code section. Need clarification.

 

[GoldDigger]

What does NEC 250.30(3) Exception 2 really mean? I have an inspector that suggested the grounding electrode conductor of the secondary side of a dry-type transformer be connected this way. But it's a bit unclear to me what is trying to be said in this code section. Need clarification.

What code cycle? I do not find that number in [2011].

 

[Shujinko]

NEC 2008

 

[Dennis Alwon]

That should be 250.30(A)(3) except. 2

 

[Shujinko]

Yes, correct Dennis sorry for the typo!:ashamed1:

 

[Dennis Alwon]

This is talking about a SEPARATELY DERIVED SYSTEM which I believe your transformer is one. It appears to allow the grounding electrode conductor of the service to be used for the separately derived system in some cases

 

[Dennis Alwon]

Here is the article

 

[iwire]

In my opinion it only applies to service switchgear that contains a factory installed SDS.

Most dry transformers are not listed as service equipment.

But I could be wrong.

 

[Shujinko]

We are installing a new 45 KVA transformer in an existing auxiliary electrical room. The AHJ in this case prefers to go all the way back to the building grounding electrodes in the main electrical room rather than just install ground rods locally on the secondary side of the transformer as permitted by 250.30(A)(7) Exception #1. Does that make sense?

 

[david]

I think tying into a grounding electrode that is part of the established grounding electrode system for the building makes sense. You would usually tie into the closes grounding electrode to the separately derived system.

 

[texie]

We are installing a new 45 KVA transformer in an existing auxiliary electrical room. The AHJ in this case prefers to go all the way back to the building grounding electrodes in the main electrical room rather than just install ground rods locally on the secondary side of the transformer as permitted by 250.30(A)(7) Exception #1. Does that make sense?

250.58 requires you to use the same GES for all SDS systems and services in the same building. This would be true in all code cycles.

 

[sbutler]

I agree with David. Tying to the closet established grounding electrode system makes more sense on a couple of levels. First, is cost. Second, running all the way back to the main electrical room leaves more room for it to become damaged and/or disconnected. I would tie it to the nearest building steel provided it is properly connected. I believe if you explain this to the AHJ, they would agree.

 

[iwire]

I agree with David. Tying to the closet established grounding electrode system makes more sense on a couple of levels. First, is cost. Second, running all the way back to the main electrical room leaves more room for it to become damaged and/or disconnected. I would tie it to the nearest building steel provided it is properly connected. I believe if you explain this to the AHJ, they would agree.

Building steel is great when it exists. Otherwise you end up running a GEC all the way back to the service equipment. This happens to us in old brick and wood mill buildings. You can run a common GEC around the building and tap onto it with each SDS.