Transformer grounding electrode conductor

[Dennis Alwon]

The basic question is do all transformers need to have a grounding electrode conductor. Obviously, a doorbell transformer doesn't but what article explains this?

Also is a grounding electrode conductor only required where a neutral is derived thru the transformer as in a 2 wire feed to a 240v transformer primary with a 120 v secondary?

 

[infinity]

Look at 250.20(A)(5)Ex(3).

250.30(A)(5)Exception No. 3: A grounding electrode conductor shall not be required for a system that supplies a Class 1, Class 2, or Class 3 circuit and is derived from a transformer rated not more than 1000 volt-amperes, provided the grounded conductor is bonded to the transformer frame or enclosure by a jumper sized in accordance with 250.30(A)(1), Exception No. 3, and the transformer frame or enclosure is grounded by one
of the means specified in 250.134.

 

[Dennis Alwon]

Thanks Rob, I was pretty sure of it but we had a discussion last night with the local boys here in NC and some said the grounding electrode conductor only needed to be connected if a neutral was derived from the transformer.

 

[winnie]

Were they confusing 'neutral conductor' with 'grounded conductor'?

 

[Dennis Alwon]

Were they confusing 'neutral conductor' with 'grounded conductor'?

One of the members said that he wired a transformer and the inspector asked him if the transformer derived a neutral. He said no so the inspector said that he didn't need a grounding electrode conductor because of that.

 

[ron]

One of the members said that he wired a transformer and the inspector asked him if the transformer derived a neutral. He said no so the inspector said that he didn't need a grounding electrode conductor because of that.

A wye secondary will always have a derived neutral, but whether you bring it out in your secondary feeder depends on if you have L-N loads. If you don't need the neutral downstream, you still have a derived neutral at the transformer needing a N-G bond and a GEC.

 

[don_resqcapt19]

One of the members said that he wired a transformer and the inspector asked him if the transformer derived a neutral. He said no so the inspector said that he didn't need a grounding electrode conductor because of that.

Even ungrounded separately derived systems require a grounding electrode system and a grounding electrode conductor. The only difference in the grounding and bonding rules for an ungrounded SDS vs a grounded SDS, is that the grounded SDS will have a system bonding jumper and the ungrounded one will not. Everything else is identical.

 

[Dennis Alwon]

If I have a transformer 100 feet from the building, then can I drive an electrode (ground rods) or do I have to go back to the electrode in the building where the feed comes from. I assume the rod is okay

 

[Dennis Alwon]

I suppose it doesn't matter if the transformer only serves one piece of equipment it still needs the grounding electrode conductor. Next question is why? Is it because it would be a separately derived system?

 

[Strathead]

I suppose it doesn't matter if the transformer only serves one piece of equipment it still needs the grounding electrode conductor. Next question is why? Is it because it would be a separately derived system?

If I have a transformer 100 feet from the building, then can I drive an electrode (ground rods) or do I have to go back to the electrode in the building where the feed comes from. I assume the rod is okay

I have to make a couple assumptions because the question isn't clear. I assume you mean a ISOLATION transformer fed from the building to the line side and then it feeds a load that is not in the building. If this is so, you need an EGC (2510.122) feeding the transformer, on the secondary side you need the grounding electrode system/bonding jumper at the transformer, through the first means of disconnect following 240 tap rules. Then you again have an EGC to the equipment.