I have a horse barn that is 1014 feet of 1.5" conduit away from the main house panel. The main panel is 400 amp 240/120 volt and I have left 100 amps for use in the barn. My current electrical needs in the barn are 2 - 1/2hp motors, one for a gate and one for a hot walker, and a small fridge that is rated at 1.3 amps, a tankless hot water heater rated at 1.04 amps and a total of 3000 watts of inside and outdoor lights. All loads are 110 volts. What would be the most economical way to run wire to the 100 amp subpanel. I know the load is much less than what the panel is rated for, but I would like to allow a little room for future expansion. I have been exploring boost transformers, trying to keep the wire size smaller and cheaper. Please make your suggestions specific with model numbers and wire sizes including a ground wire size. Thanks.

Wow, is your barn in the next county? It may be cheaper to move the barn.

All kidding aside:

I added your loads, rounded the numbers up, I arrive at a balanced load per leg of 25 amps each 120 volt leg. Doubling that to 50 amps per leg to allow for future expansion, using a 400 MCM Al wire will produce a 3% voltage drop, which is the maximum recommended allowable voltage drop for a feeder.

Here is a website that lists 3 wire URD cable, however, no 400 MCM, the next size up is 500 MCM, which will help with additional future load and reduced voltage drop.

Aluminum URD Cable- 600V- Triplex 90°C For Direct Burial on Custom Cable Corp.


I am not sure the cost of this cable. Best for you to find a local supplier that can access and price the product.

With this you can compare the cost to using transformers. To provide for an 80 amp load, you will need two 25 KVA single phase transformers with 480 volt primary and 120/240 volt secondary. These can cost approximately $700.00 each.

See the attached catalog page from the website:

Acme Electric Corporation Product Catalog

Using these two transformer, you can reduce the wire size to #2/0.

Along with the cost of transformers will need to add the cost of circuit breakers for both primary and secondary protection of both transformers, allow $200.00 for two 250 volt disconnects and $400.00 for two 600 volt disconnects.

As long as there is no other metallic paths between the two buildings, you can use the 3 wire feeder method, and drive ground rods at the subpanel at the barn, and connect the neutral and equipment ground bar together at the subpanel. If an equipment ground wire is run with the feeder, ground rods are still needed at the subpanel, however, the neutral and equipment ground would not be connected together.

You will need to compile a bill of material for both plans to see which is the less costly. I think you may find just using the larger #500 MCM cable without the transformers will be the least expensive.

I hope this helps, this is quite a project to design ,layout and price, never mind install.

I'm with tk on this!

Is there any utility power closer to the barn?

Hey Washington! Where you been, month long vacation? About time you get back here. Missed you.

Thanks for the info. There is no utility power any closer than my main panel.

I looked up the cable you mentioned TK. It has an OD of 2.03" and I only have a 1.5" conduit. I know I could direct bury it, but would rather not for ease of replacement if there ever was a problem. The cost was $5888 per 1000 feet.

I figured this cable would be costly, but not that much. Price out the transformer method, looks like that may be cheaper. As far as the 1-1/2" conduit, it is too small for either method.

Let us know what you decide to do.

Was on vacation for two weeks.

Thanks for the welcome back! :)