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Discussion Starter #1 (Edited)
Running some power to a barn ~275 ft from the house. I plan to put in a 100A main panel (with the nuetral and ground bars seperated) As a sub panel so I'll have a quick disconnect without having to run 300 ft to the house.

Current draw in the building will be between 50&60A as it will only be myself in there and I can't possibly think when or how everything would ever be on, i.e saw/compressor/heater/router etc.

I added up the big amperage draws, and the saw/compressor and heaters total 52A. Knowing how the building is wired and such I'll never run all the heaters at once as the building is divided into seperate rooms. My only concern would be compressor kicking on. Lighting will most likely be flourescent or led so I'll have low draw there. Ideally I'd feel better if I had 70A available for the random turn on of the compressor.

Now to my question, I was told 2/2/2/6 would supply close to a 100A, but at that distance it'll be closer to 60A. I'm running conduit in ground and want to be sure that I'm in the ballpark for my wire size. I saw depot has what they label service entrance wire (wrapped in grey sheathing) for a decent price. Is this acceptable to use for that distance of a run? I figured the sheathing would be nice to keep the wires somewhat manageable.
The other option they had was three individual (2/2/2) wires loosely twisted together which I think was direct burial for even cheaper but I'd have to get the ground seperately, and either way I'd still want to run it in conduit for any future use and for the fact I don't feel like digging a 24" deep trench. I also read somewhere that you can do 1 ga for the hots, a smaller ga like 2 for nuetral and then a 4 or 6 for ground. Just like everyone, I'm trying to be cheap as possible, but I don't want to get this all done and be flipping breakers all the time.

I did a quick search, but it seems everyone has way shorter runs than what I'm looking at... Thanks in advance,
 

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Master Electrician
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The gray sheathed cable you described is probably SER cable and it is not rated for underground use even when in pipe.
 

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Oddly enough I just did almost the exact same thing, but no conduit for me I direct buried the wires. If you are looking at a 3% voltage drop over 275 feet and 100 amps number 2 wire won't do it, I used 4/0 aluminum
 

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I use this for calculations. Wire Size Calculator Personally I would bury PVC, and use individual wires, rather than a direct burial cable. This gives you more flexibility in the future. And since you have to dig anyway, consider adding another conduit for telephone or intercom to the house.

Best of luck
 

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I use this for calculations. Wire Size Calculator Personally I would bury PVC, and use individual wires, rather than a direct burial cable. This gives you more flexibility in the future. And since you have to dig anyway, consider adding another conduit for telephone or intercom to the house.

Best of luck
Agreed - and less digging with conduit as direct burial cable has to be deeper (typically 18" vs. 24").
 

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Yep, all the time. From what you specified, at 100 amps you need either a #1/0 in copper or #3/0 in aluminum
 

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#4 is minimum, but at 275ft i would use larger cable.
Say 10mm, thats good for 100a.
Or even running two hot wires in parallel.
This allows for future upgrade.
 

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Discussion Starter #13
Using that calculator I get #2 Aluminum for a 300 ft run at 240 for 60A. No one around here has any #1, I'd feel a bit better knowing I'm not real close to my max amperage out there. Plus doing all this work, I'd hate to trip breakers when my compressor kicks on. I found a guy selling 4/0 4/0 2/0 on craigslist, thats a bit overkill I think.
 

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Where did you get the 50'? Your original post said 275', which in your case is half the total circuit length. You circuit is 550' total.
 

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Discussion Starter #16
Where did you get the 50'? Your original post said 275', which in your case is half the total circuit length. You circuit is 550' total.
So with that calculation it says I need 4/0 in order to get 60A. I visited the specialty electrical place today, been around for years(reliable), they calculated that the 2/2/2 would do it, I be so confused at this point. As regularguy pointed out, he used 4/0 to do his run of almost the same length.

Maybe it has something to do with continuous load etc. The way I figure it (correct me if wrong) the table saw is around 15A, the compressor says 22A but both would be less than that when it's running vs startup correct? So I took those two peak measurements, added the heaters amperage and came up with 52 amps. I also tried a different calculator on google and came up with 1/0, is this dependent on codes for different regions?
 

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Discussion Starter #17
I found another calculator that is almost identical and gives the same results as the link above but this one has a note at the bottom.....
I stuck the 50' in just to test the results..
So is the input amperage they are asking for there the amperage I'm wanting at my panel? In my mind I think input as in what the available current is from the main panel. I guess the notes answer my question about different regions
 

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So is the input amperage they are asking for there the amperage I'm wanting at my panel? In my mind I think input as in what the available current is from the main panel. I guess the notes answer my question about different regions
You have the amperage available already. The concern should be should be whether or not the voltage drop is acceptable at the assumed amperage draw.
 

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You can use Al 2-2-2-4 Mobile Home feeder (USE) in conduit and protect at up to 90A at the source. Use 240V equipment (compressor, table saw, etc.) where possible.
 
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