Outside Transformer and CB before entrance

[Tbatson44]

I am new to the forum so appreciate your help. We have an 12.47kv into an outside transformer that needs additional ground. That goes to an outside circuit breaker about 10 feet away, then into the building. There is only 3 phase 480vac no neutral going in. I am wondering about ground requirements. We will have a ground rod at the transformer, then no less than 6 feet apart at the circuit breaker. Can someone offer any advice on this? I am simply trying to help find a solution. Do the ground rods need bonded like shown in 250.48? Then from CB into building bring a ground wire into building? Thank you for any guidance and advice I can pass on.

 

[jlee405]

I don't fully understand your question. I think your scenario is similar to exhibit 250.9, except your service disconnect is outside the building. The neutral to ground at the transformer is usually done by the utility and is separate from the service disconnect's neutral to ground bond. The neutral from the transformer needs to be brought to the service disconnect and bonded again to an electrode regardless of whether or not line-to-neutral loads are supplied. See 250.24(5)(C).

 

[augie47]

I'm not clear if your transformer output is 480 or 480/277
If the transformer has a neutral connection you must bring a neutral to the disconnect.
Also it makes a difference if this is a Power Co transformer, thus you are dealing with a service; or a customer transformer and you would be dealing with a SDS. They have different grounding requirements.