wire for subpanel


Old 08-02-06, 09:33 AM
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Join Date: Aug 2006
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wire for subpanel

I am putting a 100amp 240V sub-panel in a barn, that is 250 ft from hte main panel. The wire will be buried in a trench with the water line (about 2.5 feet down) what size cable would be the min and what would allow for later upgrade to 150amp if needed? CAn AL SER be buried directly?

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Old 08-02-06, 09:43 AM
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Location: Central New York State
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No, you will not bury the electric line with the water line. You must maintain a separation. One large trench or two separate trenches are needed.

To stay with three percent voltage drop at 100 amps, you need 2/0 aluminum. I recommend four conductors, even if they aren't required. They will be if the water line is metal.

To stay with three percent voltage drop at 150 amps, you need
4/0 aluminum.
Old 09-12-06, 01:52 PM
Join Date: Dec 2004
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wires for a sub

Wouldn't he need four conductors for a sub panel. The ground and netural are not one of the same, they are isolated form each other
Old 09-12-06, 01:56 PM
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Location: Brethren, Mi
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If there were no other metal interconnections it can be done with 3, its really a new service to that building but with so many modern utilities, phones, gas, cable, etc its really not a good idea, 4 conductor is the way to go. Now why is it that we cant run the water in the same trench?
Old 09-12-06, 04:10 PM
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sberry, "OP" said "sub panel".
Water--Same trench, sure, but they must be seperated= big/wide trench.
Run seperate conduits for phone and cable and keep them at least a ft' (12") apart, some may differ, so follow along.
If you bury cable you can't enlarge/expand, without digging it up and putting in larger cable.
Old 09-13-06, 08:12 AM
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In my opinion, mobile home feeder cable is good to use in this situation. You can buy it from an electrical supply house in four conductor 4/0-4/0-2/0-4 aluminum configuration good for 150A at 250ft. It can be directly buried without conduit (minimum depth of 18", but go 24" since you'll have trenching machine). The cable insulation is typically XLPE which is very durable for underground installation. It is also probably the cheapest at about $4.50 / ft.

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