Running underground service to garage 300 feet away...

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Old 07-08-14, 07:01 PM
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Running underground service to garage 300 feet away...

Hello,
I am new here, so thanks in advance for any advice!

I just moved to a new home which has a large garage about 300 feet away. It did not have electical or gas run to it, so I am in the midst of doing that. Gas is done, now its the electrical.

I was able to have an underground construction company drop a 1.5 inch continuous PVC from my home, down to the garage which is just about 300 feet away. I am installing a 100amp subpanel but would be okay with 60 amp service for a few years. My primary use of the garage, is the basics (lights, outlets, window AC). I do plan on doing some woodworking and using chop saws, table saw, etc.

I am on a budget and would like some advice on the wire to purchase to run through the conduit? Copper vs Aluminum? Menards has a #2 wire on sale this week and was going to get that, but need a second opinion. Let me know if you have any questions, otherwise I appreciate the advice!

Todd
 
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Old 07-08-14, 07:23 PM
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A 60 amp service should be more the enough. For a 60 amp service at that distance assuming actual load never exceeded 50 amps #4 THWN copper would give you a voltage drop of 3.9 percent borderline but acceptable. I'd guess though actual load probably wouldn't even reach 50 amps. At 40 amps actual you'd be at 3.1% very close to the recommended 3%. In addition to the three #4 you will need a #8 for ground.

Are you using a 100 amp main breaker service panel as a sub. That is usually the cheapest if you get a kit. You will need to buy and add a ground bar to the subpanel and install a ground rod at the subpanel. Neutral isolated ground bar bonded.

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Old 07-08-14, 08:07 PM
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At 300 feet I would suggest going with the aluminum. The #2 should work just fine. With a full load of 60 amps, the voltage drop is the same as the #4 copper Ray quoted.

Note: I am in your same location MN and looked at the ad. The only aluminum I see is USE-2. I do not recommend pulling that into the conduit, it will be a PIA. You should use individual conductors like XHHW.
 
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Old 07-08-14, 08:36 PM
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Ray -
Thanks for the response. I would use a main as a sub. My brother who is much more adept at electical than myself will be helping with the panel and connections. I did plan on getting a kit, because it made sense and allowed for future expansion. So to be clear, you would use this #4? #4 Black THHN Cable (In the ad it does mention it is rated for THWN as well). I wasn't real clear when you mentioned "three #4". Below is the link.

http://www.menards.com/main/electric...830-c-6441.htm

Additionally I would add the ground as suggested. I dont mind going to the #2 either, but its good to know that the #4 copper will work.
 
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Old 07-08-14, 08:42 PM
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Tolyn-
Im curious why the aluminum? Most people have recommended copper, but I have been looking into aluminum as well. Would you then direct bury that?
 
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Old 07-08-14, 10:44 PM
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I wasn't real clear when you mentioned "three #4".
You need four wires. You need two hots and a neutral. That is three #4s. Normally on 60 amps you can use #10 for ground but because you are up sizing due to distance you need #8 for ground. Either aluminum or copper is fine but aluminum needs to be larger to carry the same amps. Aluminum is cheaper. USE-2 can be direct buried. It would just be sleeved with conduit for protection where it enters and leaves the ground. XHHW is the approximate* aluminum equivalent of THWN copper. (Most copper wire is dual rated THHN/THWN but corporate that rights the adds don't have a clue and calls it THHN.)

*Different insulation on XHHW and THWN.
 
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Old 07-09-14, 03:29 PM
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You mentioned the aluminum wire so I went with that.

Some aluminum wire can be direct buried, but you mentioned you have 1.5" conduit already run so why not use that? Aluminum wire is lighter to pull in, and less expensive to buy. Copper is the best, but is pricy. Your run of #4 copper will cost you about $750 (not counting the ground wire) #2 Aluminum would be less than half that.
 
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