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Want to run wire 1000 feet under ground from pole to house. Will be using 100 amp service single phase. Would like to know what size gauge of wire should I use.

  • Are you sure it's single phase? – Machavity Feb 15 at 17:48
  • Is your meter at the pole, or at the house? – ThreePhaseEel Feb 16 at 0:50
  • Also, who is your electric utility? – ThreePhaseEel Feb 16 at 1:01
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Traditional, aka "nobody ever got fired for recommending this"

1000 feet underground, split phase 120/240V service, 3 wires, this is the main service to the house (so we get a favorable 83% derate on NEC 310.15b7, so calculating for 83 amps). Your choices are

  250 kcmil aluminum at 6.84% voltage drop,  $3,300
  400 kcmil aluminum at 4.88% voltage drop,  $5,400
 1000 kcmil aluminum at 2.80% voltage drop, $11,000
   3/0 AWG  copper   at 6.06% voltage drop,  $9,000
  250 kcmil copper   at 4.48% voltage drop, $12,000
  500 kcmil copper   at 2.86% voltage drop, $24,000

Some people are really hung up on 3% voltage drop. Other people are really hung up on using aluminum nowhere ever, and ignoring the actual facts. Start a Kickstarter and let those people pay the cost differential!

All these wires will also accept 200A service. However voltage drop will be higher. Voltage drop is proportional to actual current being flowed at the moment and has nothing to do with nameplate ratings.

Transform the problem

Now, we can ease the pain by stepping up the voltage for the long haul. We will use two transformers back to back. These transformers are about $1,000 each for ones ample to your current draw.

In between the transformers, voltage is stepped up, which means current steps down by the same proportion, so volts x amps still yields the same. If we double from 240V to 480V, current halves from 100A to 50A. 240V to 600V (the max for common wires) drops current to 40A. We still get to derate 83%, giving 32.75 amps. So...

   4 AWG aluminum at 5.05% voltage drop, $  500
   6 AWG copper   at 4.89% voltage drop, $1,100
   1 AWG aluminum at 2.68% voltage drop, $1,000
   3 AWG copper   at 2.60% voltage drop, $2,000

WOW, that savings on wire is huge, and way more than pays for the transformers in all cases. Here, it seems like the winner is #1 aluminum if you intend to fit 200A service in the future, otherwise #4 Al.

I wasn't able to find any wires in the 6-7% voltage drop range, because the next smaller wire was giving 8-10% voltage drop.

This is priced based on only 2 wires. There is no point running a ground wire 1000 feet, even if this wasn't a double-isolated, doubly separately derived service, which it certainly is. There is no value whatsoever to grounding your house to a point 1000 feet away. This will be its own full and proper service, and it will absolutely depend on local grounding at the house, but that was already required.

Theft

There are two ways to go: direct burial, or conduit. Direct burial must be trenched 27" to allow 24" cover. Conduit can be covered 18" (plastic or EMT) or merely 6" (rigid or IMC conduit).

If you work in conduit, it is a foregone conclusion that some hick will break into your remote service panel, cut your leads, tie 'em to his truck's ball hitch, drive away with your 1000’, and spend the month trading chunks of it for meth. Or worse, just cut the wire in a failed attempt to do that, and leave you 6 inches short on a 1000' run.

For this reason, I would definitely bring the conduit to a wiring trunk a short distance from the house and remote site, bind the wire in some way so it can't be pulled out (or so the short bit pulls out), and then bury and hide the trunk. This also helps you if your distance proves to be a little more than 1000', position the trunks a little less than 1000' apart so you can just buy full spools.

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    Can you include prices for the wire sizes with transformer for comparison with the top set of prices? – manassehkatz Feb 15 at 18:37
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    @manassehkatz yeah, I was... I had to capture my work so far, since Google alone would not give me prices on these small wires, I had to actually navigate into websites to see. That brings the risk of my browser reloading this page, and wiping my work so far. I am stuck on iPad, they are just not intended for work like this. – Harper Feb 15 at 19:06
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    I have 2 transformer setups like this on my farm, smaller but both at 600v. I found the transformers on e bay and saved quite a bit more. I did install a fused disconnect on the primary of both remote transformers but the savings was over 1/2 of what it would have cost.+ – Ed Beal Feb 15 at 23:18
  • Would it be possible for him to ask his utility to serve him at 480VAC? – ThreePhaseEel Feb 16 at 1:01
  • @ThreePhaseEel interesting notion, if they are providing a transformer just for him. We own our HV transformers but we,re an industry. – Harper Feb 16 at 1:05
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That is a long distance you have to derate the wire and go with a larger size because of the voltage drop over that distance number 2 copper is rated for 115 to 130 amps depending on what you get

1/0 aluminum is rated for 120 to 135 depending

Would def go with either one of those sizes

Or even bigger..

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I would think that 1/0 Aluminum would be sufficient. It's oversized so it should handle the voltage drop. You could probably get away with a single USE-2 cable buried between the pole and the house

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First thing I'd do is be sure you are willing to commit to 100A service - you don't want to have to upgrade this for a car charger or something someday.

At this distance, it may work out better to either use step up and step down transformers, or have the power company set the utility transformer on the property closer to the house. I'd look into both options. The power company may not offer the service or may want a small fortune, or actually they may want a large fortune, but then the transformer is theirs to maintain.

At 1000 feet and 100 amps, I'm getting 2/0 copper or 4/0 aluminum to keep the voltage drop under 10% and that's quite a bit of voltage drop. At 200A it goes off the charts. If you step up to 480V things come much more in line and depending on the transformer you may be able to adjust for some of the voltage drop.

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