Our main service entrance comes from the Utility Co. at 69kV, is stepped down to 13.8kV, and distributed to unit substations throughout the campus. At one of the buildings we have an outdoor transformer with a 480/277 volt, 3Phase secondary. Would Section 250.24(A)(2) apply to this transformer (i.e., "at least one additional grounding connection shall be made from the grounded service conductor either at the transformer or elsewhere outside the building"), or is this Section only meant for Utility transformers?
Nec 250.24(a)(2)
- Thread starter JohnEE
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Yes it would apply to the transformer. Utility Transformer, by that I think you mean is a transformer owned and operated by the Utility Co..
- Location
- Illinois
- Occupation
- retired electrician
John,
250.24 only applies to utility supplied services. I am assuming that primary for this transformer is not utility owned. The rules in 250.30 and 250.32 apply to your system.
250.24 only applies to utility supplied services. I am assuming that primary for this transformer is not utility owned. The rules in 250.30 and 250.32 apply to your system.
- Location
- Illinois
- Occupation
- retired electrician
John,
I should also add that the rules in Article 225 also apply.
Electrically the system is the same as when it is owned by the utility, but since it is not utility owned, the rules change. There has been some movement towards making the rules the same. One example would be 240.21(C)(4) which permits an unlimited length for outside secondary circuit conductors without overcurrent protection. This was added for systems like yours and makes the NEC rule match how the utility would install the same system.
There is a task group working on a new article for medium voltage systems for the 2011 code and I would expect to see more changes for systems like this.
I should also add that the rules in Article 225 also apply.
Electrically the system is the same as when it is owned by the utility, but since it is not utility owned, the rules change. There has been some movement towards making the rules the same. One example would be 240.21(C)(4) which permits an unlimited length for outside secondary circuit conductors without overcurrent protection. This was added for systems like yours and makes the NEC rule match how the utility would install the same system.
There is a task group working on a new article for medium voltage systems for the 2011 code and I would expect to see more changes for systems like this.
Team-MEI
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- Vancouver, WA
Makes sense; changes in ownership should not be the deciding factor in different ways to install something.
Does anyone know how to contact this task group?
Does anyone know how to contact this task group?
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