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I'm building a barn that is 550' away from my house and need to power it. I would like to have 100 amp service from my main house board (200 amp). My house is fed with the typical 2 conductors. I am in Ontario, Canada.

I would like to stick the cable in the ground and use some sort of conduit like 2" likely 2 1/2" PVC shed 80 pipe if this is cheaper than an armoured cable.

What I actually Ended Up Doing The local (Rockwood, Ontario Canada) inspector gave me two options. 1) pull 300 MCM or 2) parallel 3/0 Aluminum 3 conductors director bury, both needed a ground back to the main panel (sized to cable). So....... Based on that I took Option 2, Cost of $3,800 for cable and ground + $1000 for Big-O (two runs) turns out my barn when finally located was 650ft, location was selected while I was in the EU. I had to put the cable inside Big-O to protect it because I didn't want to put 6-4" of clear sand below and above the cable.

What I learned My Electrician is at the mercy of the local inspector. They books all said I need to run single pull of 3/0 or at worst 4/0 but, they can't make a decision because the inspector as the say. Simplest means is to get the inspector out and get him to bless the project.

No One would do the Transformer Option, and the Inspector wouldn't approve it. My local Utility provider came up with a plan for about $25K to get me 600 amp service and back feed the house. needing 4 poles, high side cabling, a transformer, and easement and a tone of work by me along with a pad and remote meter. So that went nowhere.

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    Is it possible to get a second service drop from a nearby utility pole? – Tester101 Jul 27 '16 at 15:25
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    Sorry I live in Canada, Ontario – KA.Barn Jul 27 '16 at 15:25
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    Possibly, you'd have to discuss pricing with your local utility. However, extending a 120/240V single split-phase circuit 550' might be more costly than you'd think. – Tester101 Jul 27 '16 at 15:32
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    If you want those wire sizes you'd need two transformers and a lot higher voltage on the line (which might not be OK for residential, I don't know, and I know Canadian rules even less.) – Ecnerwal Jul 27 '16 at 15:44
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    Unless your use is VERY limited you are almost never better off with a generator. They are Very Expensive Power. – Ecnerwal Jul 27 '16 at 16:00
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This application has "transformers" written all over it. A big factor in AC vs DC power (Tesla vs Edison) being the ability to haul it long distances. And this right here is where that comes into play.

In every single scenario, your barn needs its own earth grounding system.

Plan 1: Conventional sub-panel (as discussed elsewhere)

Wire cost: $4000. (about a 25% margin over the best prices I can find).

That plan only makes sense if money is no object and the goal is to stay "DIY friendly". But it still won't be, because of the miserable pulls with huge wire (unless you upsize conduit to about 4", not least, because the bends are wider radius.) The only benefit to all this is avoiding transformers. Since this scenario is well covered by other answers, I'll won't elaborate.

Plan 2: Use a transformer to make the barn a main panel.

Wire cost: $2000. Transformer cost: $900

You only need 2 of the huge 350kcmil wires. You feed them with 240V and they go to the primary side of a 25kva transformer. The transformer removes the need to run a "ground" and "neutral" wire (but the primary and secondary sides are different). Your barn is now a main panel. L1, neutral and L2 come off the secondary of the transformer. The transformer and the barn panel are grounded to the barn's grounding system.

You may be able to reduce the size of the wires somewhat, because the transformer has "taps" to compensate for voltage drop.

Plan 3: Also pump up the voltage for the long run.

Wire cost: $300. Really. Transformer cost: $1800

This takes two 4-AWG (maybe 6) AL wires. Instead of one 25KVA transformer, you get two -- with a higher voltage primary, within the rating of the cable you plan to run. So if the cable rating is 600V (most likely), get 480, 575 or 600V transformers (those last two are a thing in Canada). These voltages are serious, but still within the range of common panels and wire. Call an electrician for the final review, megging and hookup of the higher voltage stuff.

You backfeed the secondary of one transformer with 240V from your panel. The primary feeds your long conduit run to the other transformer's primary, which knocks it down to 240V on the secondary. As above, the barn panel is a main panel which gets L1, neutral and L2 from its transformer, and ground from the barn's grounding system.

Plan 4: Tie into the high voltage supply

Wire and transformer cost: ???? depending on voltage rating and delivery.

The power company transports power across farmland at a much higher voltage like 600V or 2400V, and then have a transformer at your house to knock it down to 240/120V. I imagine you've already talked to the power company and asked them the cost of wheeling their high-voltage to your barn and provisioning their transformer and meter, and didn't care for the answer.

I am saying, see if it is feasible to buy their power on the high side of their transformer, and take responsibility for the pole line, underground, transformer etc. It's sorta like "rent the cable modem or buy one". Used transformers can be had. Of course touching their high-voltage is electrician territory, but you can do all the grunt work, so he megs a few things out, connects 2 wires and throws the switch. There's no reason to pay an electrician to trench conduit or punch holes in walls.

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    Cool so if I understand Option 3, the idea is take 240V - transform it to 600V for the long haul,(Reducing cable size) then transform it a second time back to 240V. So there is a single cable to the barn. the barn just needs a grounding system. I like that I have #4 Copper laying around, transformers are as you mentioned quite reasonable. – KA.Barn Jul 27 '16 at 19:01
  • Quick Q... Option 3.. do you think it is possible to back feed the house? (yes put in a transfer switch and break off a few circuits in the house) My goal is to have the possibility to use an engine driven welder (Ranger 225). As backup for the barn and house. – KA.Barn Jul 27 '16 at 19:06
  • And the barn will need a grounding system no matter what. – Harper Jul 27 '16 at 19:29
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    Backfeeding power from the barn will work through the transformers, but you have to solve the interlocking problem definitely. It's not the same as backfeeding from a subpanel, as the transformer output is its own source of service. For instance I did not advise hooking up neutral to the transformer secondary at the house, and you would need that to usefully backfeed. – Harper Jul 27 '16 at 20:13
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    Yes, neutral is a big issue. The power company's transformer is center tapped, but not perfectly, because of manufacturing tolerances. The other transformer will also have manufacturing tolerances. If you hook up the other transformer L1 + neutral + L2, the two transformers will flow high currents fighting each other (over the definition of "neutral"). So you can't do that. Trying to backflow this circuit for a barn-side generator is a rather ugly problem. I'd put the generator at the house and bedone with it. – Harper Jul 27 '16 at 23:56
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Since you didn't include a load calculation for the barn, I used the full 100 amperes for the following calculations.

A 100 ampere feeder would likely have to use 3 AWG copper conductors (1 AWG aluminum), so that's where you'd start at. You'll want to limit the voltage drop as much as possible, which would mean installing larger conductors. A rule of thumb, is to reduce voltage drop to about 3%.

240 volts * 3% = 7.2 volts

Using copper conductors, you'll have to use 4/0 conductors to reduce the voltage drop enough.

2 x 550' x 100 Amperes x 0.0000608 ohms/ft = 6.688 volts

Aluminum conductor means using 350 kcmil conductors

2 x 550; x 100 x 0.0000605 = 6.655 volts

When you start working with this size wire, you're going to need special tools and knowledge. Which means it's likely out of the DIY realm.

If you want 120/240V at the barn, and not just 240V. That will require three current carrying conductors, and a grounding conductor. So you'd be looking at using 2 1/2" Schedule 80 PVC conduit.


Having a second service drop installed nearer the barn, might be an option.


High voltage lines and transformers are likely not a good fit for a DIYer, so that's probably not an option.


Other options would include generating your own power via fuel, solar, wind, water, etc. Though those systems are likely cost prohibitive.

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    4x 350kcmil Al is also not a good fit for a DIYer, since it will be impossible to pull without a truckload of special tools, and there is not a 100A panel in the world that can take lugs for 350kcmil. I think high voltage and transformers is the way to go, not DIY of course. – Harper Jul 27 '16 at 15:57
  • I happen to have 500 MCM as a utility feeder (ouch.) It was crimped to 4/0 in the meter box in order to fit the connections on the meter (by my licensed electrician with a huge hydraulic crimper and listed crimps, not by me.) Thus does voltage drop and being able to connect the wire intersect, in the real world. – Ecnerwal Jul 27 '16 at 16:17
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This is one of those perennial questions where the answer is both simple and complex.

If you actually expect to USE 100 amps at the barn, you plug 100 amps and 550 feet into a voltage drop calculator with various wire sizes and materials, shooting for 3% or less voltage drop. But if you plan rather for the actual loads you will be running, the wire size will virtually always be much smaller than if you plan for 100 amps. I get 350 kcmil aluminum for the 100 amp case and a strict 3% or less condition. 4/0 copper gives the same voltage drop (2.8%) for 240V service at 100 amps. If your actual loads turn out to be 67 amps, wire size required drops to 2/0 copper or 250 kcmil aluminum (though 4/0 aluminum is REALLY close at 3.1%.)

The ground (not neutral) can be a smaller size, though it does have to be proportionally increased to match the increase in size due to voltage drop of the current-carrying conductors.

In practical terms, aluminum wire will almost certainly be far cheaper, even though you have to use a larger size relative to copper. While small size aluminum wire as used for a while in branch circuits is a bad, bad, idea, large size aluminum wire is both normal and safe and a lot cheaper than copper. If in doubt, get an electrician in to make the actual connections correctly.

You will need to run 4 wires - Line1, Line2, Neutral and Ground, and Neutral will not be connected to [will be isolated from] ground (and ground will be connected to a grounding system at the barn.)

  • Can you elaborate about why large size Aluminium wire is OK but a bad idea at small sizes in branch circuits? That snippet sounded intriguing. – curious_cat Jul 27 '16 at 15:54
  • I agree with the aluminum comment.+ here is a voltage drop calculator link. so you can put in copper or aluminum, the max voltage drop should be no more than 3% at the panel under load. – Ed Beal Jul 27 '16 at 16:11
  • It's a combination (AIUI) of the alloy used and the geometry /design of the connectors. In part the fact that they are single-strand comes into play - as they heat up in use, they expand and flow, and when they cool off they shrink, but having flowed, don't fit as tight as when they were new, leading to more heating... If you have aluminum branch wiring,this should be required reading: cpsc.gov//PageFiles/118856/516.pdf but it does not really get into why the large stuff is OK. This wikipedia article does, a bit: en.wikipedia.org/wiki/Aluminum_wire – Ecnerwal Jul 27 '16 at 16:11
  • @Ecnerwal, thanks for the help. My only concern with undersizing the feed from the house to something like 67amps (thus 2/0 copper or 4/0 aluminum) is that what if I pull more? Or would I more realistically put in a sub panel with a breaker at 60 amps? – KA.Barn Jul 27 '16 at 16:17
  • You either look at your current and expected loads while holding tight to your wallet, or you reach into your wallet and go for the maximum. WIth LEDs the lighting load goes down to diddly in most cases, so you look at 240 loads that are going to be on at the same time (you probably won't woodwork and weld AT THE SAME TIME) and you balance 120V loads that will be on at the same time as much as possible (15 amps at 120 on one line and 15 amps at 120 on the other line are 15 amps at 240, not 30 amps, load-wise - if on the same side of the line, they are 30 amps - balance is good.) – Ecnerwal Jul 27 '16 at 16:24
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I sure am glad I don't have your problem. :-)

Besides the choices of using long heavy wire, a second meter, transformers, etc. Another option might be to install a generator.

A capacity of 100 amps at 240 volts is 24,000 watts (24 kw). Costco carries those online. Such generators run about $5,000 with all the options for failover, but if there is no other source of power, you can reduce the cost by perhaps $1000 since no transfer switch is needed.

For an ordinary shop situation without welding, 7 kw should be more than adequate. Around here (Oregon), they sell this one in stores which is quiet, uses propane or gasoline, can run 240 volt devices, and is only $800. Personally, I am trying to find justification for having one. :-) enter image description here

  • This seems like it would be the most ideal solution. – Evan Carslake Jul 27 '16 at 23:56
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    "Personally, I am trying to find justification for having one. :-) " - the justification is that you want one, surely. – immibis Jul 28 '16 at 0:38
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    "Sooner or later the cascadia fault is going to rip and throw a giant 9.0 earthquake. The grid is likely to be fubared for weeks or months afterwards." Sounds like a valid excuse for the more densely populated parts of the state. If you're in the eastern half swap out whatever the most likely natural disaster is where you are into the excuse. – Dan Neely Jul 28 '16 at 11:11

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