Subpanel Ground

datafan

I am bidding a 100 Amp service for a new shed. The shed is 250' away from the house and is not connected to the house with any metalic objects (no water or gas lines etc.). The house is up on a wooded hillside above the shed, it will require 125' of trenched wire across the yard from the house, install a pole and run a stack up it to convert to overhead on the top edge of the steep wooded hill, continue the overhead to a post 75' down the hill and continue overhead to the stack on the shed.

Finally my question (s).
Per code, do I need to run 4 wire and treat this as a sub panel with no ground to neutral bond screw?

Or can I just run urd and triplex (3 wires) and sink a ground rod at the shed.
And if this option, do I install the bond screw and tie the neutral and ground together in the subpanel or leave it out?

Perhaps both methods meet code? If so the second is less expensive.

I don't have my code book here with me and I am not understanding the information I have managed to find online.

Thanks...

mdshunk

You only need to run a 4 wire if you have "other metallic paths" between the two structures, and you'd set it up as a subpanel. Even though not required in this case, it is the better option if you wanted to go "above code".

Yes, if you only run 3 wire, then you must install the bond screw or bond strap. You sink a ground rod out there regardless of which wiring scheme you use.

There are some special rules for required main disconnects for residential accessory structures that will be of some concern to you. Are you famaliar with those codes?

You mention that you intend to use URD for the underground portion. It may interest you to know that URD is not a code recognized conductor insulation type, and it can't be brought inside the house's panel to hook up to the feeder breaker. Some URD is dual rated as RHH or XHHW, and some is not. The compliant option would be to choose XHHW (aluminium) or THHN (copper) instead of the URD, unless your URD happens to be dual rated.

datafan

I think I am ok with it??? We have done many sub panels but always run 4 wires. Is there somthing specific you are thinking about that I may not be aware of with a 3 wire system?

I understand what you are saying here. I misspoke using URD, I use something called "sweet briar", I think that's the manufactures name but not sure, we call it sweet wire. It is 3 aluminum wires wrapped together, I don't have a piece here to look at right now, but I believe it must be XHHW??? It is rated to direct bury and also run inside a dwelling.

datafan

The wire I was refering to is Series 8000 wire. The code name for 4/0 is Sweet Briar, the code name for #2 is Stephans. I don't know who comes up with this stuff???