Service Grounded Conductor or N and G

[mshields]

I had asked this in an earlier string but the discussion went off track a bit.

I have a customer owned pad mounted transformer (1500kVA) providing a 480V "service" to a hospital. i.e. hospital is primary metered. Since the utility does not own the transformer, may this still be called a service transformer.

If I am to treat it as one, I would run a service grounded conductor in lieu of a neutral and a ground correct?

And if this is a service, I may take advantage of 230.90 which permits me to protect these secondary conductors with a device which is in series with them. i.e. in this case the main breaker inside the building in the main switchboard. Are we in agreement so far?

If this is not a service transformer because it's owned by the customer, then I'd need to provide a neural and a ground on the secondary and my protective device on the secondary side would have to be no more than 25 feet from the transformer correct?

I really appreciate your collective help on this!

Thanks,

Mike

 

[chris kennedy]

I would call the serving utility for clarification.

Service Point. The point of connection between the facilities of the serving utility and the premises wiring.

And from the commentary that follows in the 08NECHB;

The service point is the point of demarcation between the serving utility and the premises wiring. The service point is the point on the wiring system where the serving utility ends and the premises wiring begins. The serving utility generally specifies the location of the service point.

Because the location of the service point is generally determined by the utility, the service-drop conductors and the service-lateral conductors may or may not be part of the service covered by the NEC. For these types of conductors to be covered, they must be physically located on the premises wiring side of the service point. If the conductors are located on the utility side of the service point, they are not covered by the definition of service conductors and are therefore not covered by the NEC.

 

[mshields]

Service Point

Service Point

The service point in this case Chris is definitely upstream of the primary switchgear. We're actually putting in new switchgear and a new 13.2kV service. The utility brings their conductors to a manhole just ahead of the new MV switchgear, our contractor splices into these utility provided conductors at this point. Everything down stream in terms of equipment and conductors is customer owned.

So with that, would it be a correct conclusion on my part that your opinion is that 230.90(A) applies here? i.e. may I protect the secondary conductors via a device which is in series with the conductors namely the MCB in the Main incomming 480V switchboard?

 

[david luchini]

The service point in this case Chris is definitely upstream of the primary switchgear. We're actually putting in new switchgear and a new 13.2kV service. The utility brings their conductors to a manhole just ahead of the new MV switchgear, our contractor splices into these utility provided conductors at this point. Everything down stream in terms of equipment and conductors is customer owned.

So with that, would it be a correct conclusion on my part that your opinion is that 230.90(A) applies here? i.e. may I protect the secondary conductors via a device which is in series with the conductors namely the MCB in the Main incomming 480V switchboard?

No, the "service" is the 13.2kV service. The transformer stepping down to 480/277 would be a separately derived system. The protection of the secondary conductors would be per 240.21(C) and the grounding would be per 250.30.

 

[mshields]

Ahh!

Ahh!

That's good - I have full range bayonet fusing plus under tank short circuit fuses on the primary of the transformer. All I need to do is make sure the ampacity of the fuses when transposed by the ratio of the transformer does not exceed 125%?

 

[david luchini]

That's good - I have full range bayonet fusing plus under tank short circuit fuses on the primary of the transformer. All I need to do is make sure the ampacity of the fuses when transposed by the ratio of the transformer does not exceed 125%?

No, you have to make sure that the ampacity of the secondary conductors is NOT LESS than the rating of the OCPD that the terminate at (the main breaker of your 480V switchgear.

The primary fuses won't provide any protection to the secondary conductors.

 

[malachi constant]

Read definitions in Article 100 for Service Point, Service Equipment, Service Conductors and Service-Entrance Conductors.

My opinion is you don't need protection of your conductors until they hit the Service Equipment, which is inside the building. 230.90(A) applies. I haven't walked it straight through the code though (or know the hospital-related code) so maybe something else trumps it.

 

[don_resqcapt19]

Read definitions in Article 100 for Service Point, Service Equipment, Service Conductors and Service-Entrance Conductors.

My opinion is you don't need protection of your conductors until they hit the Service Equipment, which is inside the building. 230.90(A) applies. I haven't walked it straight through the code though (or know the hospital-related code) so maybe something else trumps it.

The service point is 13.2kv side of the transformer. None of Article 230 applied to this transformer. The transformer is a SDS and the secondary conductors are feeders. The overcurrent protection of the secondary conductors are covered by 240.21(C). The protection of the transformer itself is covered in 450.3. The protection of the primary conductors is covered in Part IX of Article 240.