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# wire size 250'

#1
04-21-20, 02:16 AM
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Join Date: Apr 2020
Posts: 1
wire size 250'

So I'm wiring up a 200 amp panel 250' away from pole 3 wire 120v. Just wanted to make sure I am running the correct wire which I calculated to be aluminum 600 mcm for a max 3% voltage drop. It seems large to me which is why I am here.

Any help appreciated!

#2
04-21-20, 06:55 AM
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Join Date: Mar 2010
Location: USA
Posts: 4,298
When calculating resistance of the wiring run, don't forget to use round trip distance. Unfortunately some voltage drop calculators already include that compensation and some don't so it can be confusing.

For standard 120/240 volt services and feeders use 240 volts and not 120 in your calculations.

For simplicity, voltage drop calculations are watered down. Calculation result is based on full load at 240 volts.

#3
04-21-20, 10:01 AM
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Join Date: Feb 2016
Location: United States, Virginia
Posts: 1,514
Does the 200A panel have the first disconnect after the meter? Or is there a disconnect back at the pole? I'm asking because oneway is 3 wire feeder, the other requires a 4 wire feeder.

#4
04-21-20, 11:34 AM
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120/240v - single phase - one way distance 250' - 3% max drop.

According to the calculator I use..... you will need to run 250mcm aluminum or 3/0 copper

#5
04-21-20, 12:21 PM
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Join Date: Oct 2005
Location: USA
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I get 2.68% drop at 240V and 200A with 250kcmil copper.

#6
04-21-20, 12:32 PM
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Location: United States, Virginia
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Here is the equation for VD: 2 x I x R / 1000 * FT = VD / 240 = voltage drop % (at 240v)

2 x 200 x .0847 = 33.88

33.88/1000 = .03388
.03388 x 250 = 8.47
8.47 / 240 = 3.52% total drop for 200A on 250' of 250kcmil AL
R is .0847 at 75deg.C for 250 kcmil Al per NEC Table 8

300 kcmil Al with R at .0707 will be 3% VD.

#7
04-21-20, 12:32 PM
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Join Date: Sep 2005
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Does the service wiring need to be sized to the full 200A? Have you done a demand load calc? Unless you're running electric heat or on-demand water heaters, most houses don't use anywhere near the 200A max. You may be able to down-size the cabling if your usage is lower than 200A.

(I believe you can adjust your wire size based on projected load for a service)

#8
04-22-20, 10:35 AM
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Join Date: Jan 2010
Location: United States
Posts: 10,765
Where is the meter, on the pole or at the structure where the 200 amp panel is located??