Proper gauge for long range well pump?

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Old 11-26-11, 12:42 PM
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Proper gauge for long range well pump?

I live out in the country and had on old water well cleaned out to serve as an auxiliary well. The well is 700 feet from my meter pole and I ran three pieces of 2/10 w Ground Romax (I had this laying around) as a temporary service until I could afford to buy the right stuff. The well is 100 feet deep and I am running a 1/2HP submersible pump. As long as I did not put a pressure tank system on it and just ran it wide open, it worked fine. But when I put the pressure tank system on it, it immediately burnt the first pump out. It was an old pump I already had, so I did didn't think anything off it. I replaced it with a another brand new one and it lasted about 3 months. I replaced it and the last one lasted about 6 months.

So I am thinking that my problem is the wire. I am not an electrician, but maybe 10 gauge copper is just not big enough for a 700 foot run to service a submersible pump. Now I want to replace it with a permanent service, but I am not sure what to use.

If 10 gauge copper is to small then I need to go to 8 gauge. But 700 feet of 8 gauge copper wire is a lot of money. So I am thinking 8 gauge aluminum. What do you think? Any advice will be appreciated.
 
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Old 11-26-11, 12:54 PM
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Gauge

8 gauge aluminum is no better than 10 gauge copper. Check the current carrying capacity and voltage drop.
 
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Old 11-26-11, 01:21 PM
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Is it 240v? At that distance you perhaps should be considering set of transformers to run 480v out then drop to your pump voltage. If you can find surplus transformers on Ebay the money saved on smaller wire may make transformers a cheaper alternative.
 
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Old 11-27-11, 07:11 AM
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I agree with Ray that you might want to price out some small 2:1 dry transformers to boost to 480V for the distance, but if not here's what I recommend.

Use copper wire no smaller than #8 (aluminum #6). That size is borderline even. My calculation shows that #6 copper is probably the better way to go, but there is obviously a difference in price for that distance.

If you got the transformers for each end, you could run #12 copper wire so there's a big issue on price here.

Also it could be the friction loss in 700 feet of pipe that's killing the pump and pressure system. It's a lot of work for a 1/2 hp pump to move water that distance.
 
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Old 11-27-11, 08:36 PM
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Thanks. Yeah, you are right. A friend of mine showed me a site that does this sort of calculation and it said #6 copper as well. That is a heck of a lot of money. I asked him about the transformer thing and he said that it might work but it would be less efficient. He said would look into getting me some sort of cheaper copper wire. I can't remember the name of it, but it is used a lot in the oil field. It is solid instead of strand. He said it is cheaper because it is a pain the work with.
 
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Old 11-27-11, 08:44 PM
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It is solid instead of strand
Typically, solid wire is less expensive than stranded wire. Locating solid #6 copper wire shouldn't be too terribly difficult, but it might be hard to find a supply house that stocks it. You may have to order it.
 
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Old 11-28-11, 09:34 AM
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You also might be able to find a deal on some common underground aluminum cables such as 2-2-4 URD or MHF that's used to connect mobile homes. Just beware you can't use that cable indoors and you will need an appropriate connection between the copper and aluminum.
 
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Old 11-28-11, 10:17 AM
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I'm guessing the pump is undersized for what you want to do. My well is about 120 feet from the house, but it is 700 ft. deep with the pump near the bottom. The pump is 220VAC, and works fine with #10 wire and a 30A breaker.
 
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