250.24

[scott minter]

Good Morning

I attended Mr. Holt's class Friday and Saturday in Orlando and came away with a question.

I have 13,200 volts coming from the utility to a transformer. It is a delta wye transformer.

13,200 to 480. On the secondary side the OX is tied to ground. From the transformer it travels

about 25 feet to a 2000 amp breaker /disconnect. The phase conductors and the ground are the

only wires coming over, does it need to have a neutral (grounded conductor) ?

I do not think so because the ground wire is tied to the transformer and the XO at the transformer

so a fault on the load side anywhere would travel on the ground wire back to the transformer up the XO to the source.


Thank you.

 

[augie47]

Oddly, it depends on where the service point is. In most cases the transformer will be a utility transformer and the service point will be the secondary side of the transformer,. In those cases, the grounded service conductor connected to XO is allowed to serve as the grounded and grounding conductor to the premises.
IN rare cases, where the utility service point is ahead of the transformer (such as some large industrial facilities), the transformer becomes a premises separately derived system and an additional bonding jumper is required along with the phase and grounded conductior per 250.30

 

[scott minter]

Thank you

Some more information :

The 13,200 is the line coming from a substation to a VFI then across a street under ground to the transformer.

The transformer is located inside a large industrial facility. All on a large Government facility.

The Government entity is responsible for the primary side of the transformer and its workings

I am responsible for secondary conductors and the 2000 amp breaker. Any suggestions ?

Thanks.

 

[roger]

Out of curiosity why are you calling it a "ground" wire? If as Gus says the actual Service Point is on the secondary side and the conductor is sized per 250.24(C)(1) all is good. If it does meet the requirements of 250.24(C)(1) but is identified green just change the identification.

Roger

 

[augie47]

If it's a government entity the first thing I would do is check with the inspection authority for that facility. Often they are exempt from local inspections. As you describe it, I see it as the 2nd scenario. Since the service point is ahead of the transformer, the transformer becomes a facility SDS and you will need a "supply side bonding jumper" from the transformer to the 1st disconnecting means. {250.30(A)(2)} in addition to your grounded conductor.
Details vary slightly depending on the Code cycle involved so check 250.30 in the applicable Code.

 

[scott minter]

Thank you for the help.