Mdthbs

I have a barn that is 750' from my main panel. I would like to run power down to it myself because the power company quoted some crazy high prices. I plan on burying the wire and would like to know what size wire I should go with or if it is too far to do. Any help would be appreciated. The barn is going to have lights, some outlets and maybe a 220 outlet or two in case I need to power a welder from time to time, but thats about it. I would rather go bigger in case I need to expand in the future.

Long-distance circuits are a huge opportunity to spend way too much on wire unnecessarily. Given the amount of money that is at stake here, let's debunk the usual 3% knee-jerk.

There are two huge mistakes when made when sizing circuits.

• sizing for 3% voltage drop. 3% is simply wrong. There's no support in Code for it anywhere (it's a suggestion, one place). This myth is widely spread by the companies who sell wire, for obvious reasons -- the first place they do it is in their "free" voltage drop calculators. They default to 3%, and by that they mean literally 3.00% - if a cheaper option would come in at 3.25%, they will hide it, and "blame the computer" for being too literal.


• Sizing for "breaker trip rating" instead of practical load. Remember, loads are already supposed to be derated 20% (literally, breaker should be 125% of load), so sizing to breaker is always wrong. Indeed, the simplest step of sizing to 80% of breaker usually results in a couple of wire size drops and thousand$ saved. But you should go farther, and size to actual load.

Voltage drop is proportional to current right now

Remember that voltage drop in a circuit is a function of current actually flowed. Here's what's not true: "The voltage drop the calculator says will always apply to all loads". Actually it will never apply to any loads.

Suppose someone puts in monster wire on their "50A" circuit and gets to 2.5% drop at 50A.

• You draw 10A @ 120V. You actually get 1.0% voltage drop. Not what we expected, eh?




• What happens if you have a "30A" dryer, which actually is 23A, and that actually is about 21A on the 230V side and 2A on the 120V side. So drops of 0.525%, 0.05%% and 0.575% per leg. The 240V heating element sees 1.1% voltage drop, and the 120V mechanism sees a 0.575% voltage drop.




• A 40A (9600W) heater sees 2.0% voltage drop, which it doesn't need -- heaters will work on 30-40% voltage drop.

Getting the idea how wasteful this is?

For a welder, consult with your manufacturer, but voltage drop is pretty normal for a variety of reasons inside welders, so it's probably not going to bother them all that much.

There's also a missed opportunity: Using transformers to step up voltage. All fixed-installation wiring is rated for 600V, and there is nothing wrong with stepping up power to 600V for the transition. Transformers are expensive, but on a long haul, they're cheaper than wire. Often, simply "stepping up" the circuit to 240V, and using a transformer at the far end to make 120V, is all you need. I have plenty of postings about this.

Not a lot of information to go on here but this resource:

Wire Size Calculator

May be helpful. Assuming you want 240V and a 50A capacity (based on what my welder needs) I plugged those in with 750' distance and came up with 4/0 AWG Aluminum. At this large size I think you'll find that Al is a much better value than copper.

Lots of other variables and I'll recommend that rather than direct burial you'll want to bury a conduit that is large enough to handle the 4/0 wire or something larger if you need more power in the future.

I'm going to guess that this is going to cost $5K or more. The cost of the wire alone is going to be something like $3000.