High VOltage Service Requirements

[KasseemF]

Hello,

I have a customer who oriniginally designed to have 13.8kV service steppen down by an outdoor pad mount transformer then bring servicne into their industrial building.

However they are now asking if they can use an internal dry type transformer instead and run the HV above ground to the inside of the building due to the fact that the infrasturcture of the building is already in.

My question is what type if wiring procedure is allowed according tot he NEC for this HV and what proprocedure anecessary for the use of the dry type transformer in the building.

 

[iceworm]

Hello,

I have a customer who oriniginally designed to have 13.8kV service steppen down by an outdoor pad mount transformer then bring servicne into their industrial building.

However they are now asking if they can use an internal dry type transformer instead and run the HV above ground to the inside of the building due to the fact that the infrasturcture of the building is already in.

My question is what type if wiring procedure is allowed according tot he NEC for this HV and what proprocedure anecessary for the use of the dry type transformer in the building.

Where exactly is the service point - the connection to the utility? Is it on the 13.8kv side or the 480V side (that's assuming the xfm is stepping down to 480V)?

The OP says "13.8kv service". That leads me to believe the utility is providing 13.8Kv and the service disconnect (and first OCPD) is outside and the xfm is provided by the customer. Are you thinking to move the service point to the inside of the building next to the xfm?

I tend to put the first OCPD out near the battery limits. That gives the least amount of unprotected conductors that can be attacked with cranes, loaders, excavators, and the like. Of course, then averything after the first OCPD is a feeder.

None of this matters a lot - but it does a bit.

So, specific answers to your questions:
1. If the MV is "service", then (2008) 230.202.B Covers wiring methods. That refers you to 300.37 for above ground. If the MV conductors are "feeders", that is a different set of requirements.

2. Dry type transformers in buildings are covered by 450.21 and the accompanying FPN.

Generally, MV services are not an NEC cookie cutter design. Engineering is required to meet the customer specs, reliability, and safety requirements. Usually once those three are met, the installation is way past the NEC requirements.

ice