Shore Plug at house for Motorhome


Old 07-09-04, 04:18 PM
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Shore Plug at house for Motorhome

I want to wire a shore plug for my motorhome at the house. I have a 30amp outlet today that I plan to move.

My questions is concerning the length of the run and the voltage drop due to resistance. I need to add a junction box to the existing 30 ft 10/3 wire and add another 100ft of 10/3 (which I will bury). I plan to keep my frig and one airconditioner running to keep things from spoiling. Both are 110 applicances.

I know I will get some drop in the 30 amps, but can't find a reference table that tells me how much drop. Does anyone know how I can calc the drop?

Will heating be a problem due to the length of the run and splice at the junctions box?

Advise from an electrician would be welcomed. Demand for electricans is so high, I can't get one to come out to do a small job like this!

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Old 07-09-04, 05:06 PM
Join Date: Sep 2000
Location: United States
Posts: 18,497
10/3? You only need 10/2 for a 120-volt circuit. You're going to have a wire you don't know what to do with.

If you google for "voltage drop calculator", you'll get all you need to compute voltage drop.

130 feet of #10 copper running 30 amps drops 8 volts. That's too much. You'll need #8, which will only drop 5 volts.

Last edited by John Nelson; 07-09-04 at 09:15 PM. Reason: Corrected typo. 20 changed to 30.
Old 07-09-04, 07:05 PM
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30 amp - not 20 amp

John - thanks for the response.

The outlet will be 30 amps - not 20 amps as stated on your reply. Does this decrease the voltage drop to and acceptable %?

Also - a 30 amp RV plug requires 3 wire. 1 -hot, 1 neutral, and one ground.
Old 07-09-04, 09:03 PM
Join Date: Nov 2003
Location: NE INDIANA
Posts: 111
If you use 10-2 with ground, you'll have your three required connections... black for hot, white for neutral, ground wire for ground... 10-3 will have an additional red wire that you won't need, but will have paid extra for.
Old 07-09-04, 09:14 PM
Join Date: Sep 2000
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Posts: 18,497
Sorry, the 20 was a typo. Replace the 20 with a 30 and the rest of the post is as I intended it. I think I'll go back and edit that 20 to a 30 so you can see what I meant. So you still need #8 for acceptable voltage drop, and even that is marginal. 130 feet is a long way to run 120-volt power

I guess the 10/2 vs. 10/3 thing was just terminology. Assuming you are using NM-B and/or UF-B, 10/2 is the name of the cable with black, white and ground.

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