Service Design Review

[philly]

I have posted a thread on this topic previously where I was trying to design a circuit to feed a transformer and panel and I got a lot of help and suggestions with some of the design and code aspects. I thank everyone who contributed.

I have now come up with what I think is a final design and wanted to bounce it off some of you guys.

Basically the scope of the project is to have a 100A 120/240 panel at a remote location. The distance from the closest power source is aproximately 1200ft. The following is my ciruict and design choices.

1) 70A 480V Feeder Breaker Located in 480V MCC
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2) 1200 ft of 3/c #2 AWG (To account for voltage drop)
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3) 70A Disconnect (Unfused) located at remote location (MaintananceShutoff)
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4) 25kVA 480-120/240 Outdoor Transformer
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5) 100A 120/240 panel located right next to transformer (5ft) with a 100A
Main breaker in panel.

What do you guys think of this final design? Does it meet code? Good design choices?

 

[Buck Parrish]

If 100 amp carries the load you are in good shape.


Next to the transformer , I might have went with a six 2 pole breaker panel with no main.

 

[broadgage]

If 100 amp carries the load you are in good shape.


Next to the transformer , I might have went with a six 2 pole breaker panel with no main.

Although code allows a panel without a main, provided 6 or less breakers are instaled, I dont think that it would be a wise choice in this case.

The proposed 100 amp main, is not just a dissconecting means but also protects the 25KVA transformer against overload.
If the branch circuits exceed 100 amps in total, as they might, then I believe that a 100 amp main is required to protect the transformer.

Of course if the branch circuits total 100 amps or less, then a panel without a main would be fine, and cheaper.

 

[philly]

Although code allows a panel without a main, provided 6 or less breakers are instaled, I dont think that it would be a wise choice in this case.

The proposed 100 amp main, is not just a dissconecting means but also protects the 25KVA transformer against overload.
If the branch circuits exceed 100 amps in total, as they might, then I believe that a 100 amp main is required to protect the transformer.

Of course if the branch circuits total 100 amps or less, then a panel without a main would be fine, and cheaper.

I am using the 100A main as the secondary protection for the transformer as you mentioned. It is my understanding that this secondary protection for a 3-wire transformer is required no matter what the load is. Even if the branch circuits are less than 100A dont we still need secondary protection of the transformer?

Good to hear that the rest of the feeder design looks o.k.