13.8kv to 240 transformer grounding/bonding

[codeuser1]

Our plant has an overhead 13.8kv distribution system (open air 3 phases and a static line - much like utility company; but, all owned and maintained by the plant). My question is that when a pole mounted outdoor transformer is installed to supply a buidling does it meet code to bond the transformers X0 (neutral) to the static line, a locally driven ground rod at base of pole, the neutral conductor feeding the building, and a ground conductor run in the same underground feed to the building. At the building's panel (an exterior service entrance rated panel like a residence) the neutral and ground bus are not bonded to prevent parallel current. Terminated at the building are the two hots, the neutral and the grounding conductor; additionally, a ground rod is driven at the buildling's panel and this is connected to the ground bus only. I know this would be ok for a seperately derived system just confused on the fact that the neutral to the transformer is bonded to the primary's static line (so not seperately derived right?) and the code requirements to have an additionally electrode for outdoor transformer. If this installation did not have the grounding conductor then I would drive the rod at the transformer and bond to the neutral (grounded conductor) and then another rod at the panel with that connected to the panel neutral and then have a main bonding jumper; but, since there is a grounding conductor with the two hots and neutral from the pole transformer the netural and ground should remain unbonded except at the transfomer - right?

 

[Smart $]

With the primary grounded conductor passed through, the secondary is not an SDS.

Transformer neutral-ground bond gets a ground rod.

Panel grounding gets ground rod (GES), not the neutral. These are isolated with respect to each other after the transformer.

Elsewise, you could wire it identical to a service.

 

[codeuser1]

Is it consdered a "service" then? Any idea why the code normally only shows "services" without a grounding conductor run with the grounded conductor. Grounding conductors are nearly always shown/discussed and required for SDS and feeders.

 

[Smart $]

Is it consdered a "service" then?

Only if PoCo supplies the power (you made it sound as though they do not... at least not directly)... and then it depends on where the service disconnect is located in the system. Though your plant owns and maintains the 13.8kV system, if the poco supplies the power, it must pass through a service disconnect before it is no longer a "service". If there is none prior to the panel you mentioned, then it is a service.

Any idea why the code normally only shows "services" without a grounding conductor run with the grounded conductor. Grounding conductors are nearly always shown/discussed and required for SDS and feeders.

It is considered the best method to keep normal current on non-exposed conductors while keeping potentially harmful voltage at a minimum on exposed non-current-carrying metal.

 

[chris kennedy]

Is it consdered a "service" then?

(open air 3 phases and a static line - much like utility company; but, all owned and maintained by the plant).

I agree with smart, IMO not a service.

Service. The conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served.