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I need to run a 50 amp line from my outside breaker box to plug in my RV. the distance is 400 to 500 ft. I will have an electrican do the hook ups but I want to run the piping and wire. I think the wire would be a 6-2 indoorwire that should carry the load, nothing else will be run off this wire. Suggestion?

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    Thou shalt not use "indoorwire" outdoors. ALL exterior conduit is defined as a wet location. 99.9% of it is, indeed, wet, to the point of being filled with standing water in parts.
    – Ecnerwal
    Commented Jun 24, 2015 at 22:41

2 Answers 2

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OK, a bunch of stuff to respond to:

Wire size

There are really two considerations when picking wire size:

  1. Safety. You do not want the wire to overheat and catch fire. 6 gauge is fine for 50 amps, so you're good on this front.
  2. Voltage drop. Long wires cause the voltage to drop. Upsizing the wire will counteract this. Typically you want to keep the voltage drop under 3% or so, although it somewhat depends on whether the voltage coming into your house is on the high or low end, and also what you're using the circuit for. 6 gauge wire for 500 feet @ 50 amps will have more than 8% drop, which is almost certainly unacceptable. If you want to stick close to 3% you will need 2 gauge at a minimum.

Cable Choice

Your RV hookup is probably 240V with a neutral, which requires 3 conductors + ground (not 2 conductors like a standard indoor 120V outlet).

Also, using "indoor" Romex (NM-B) is not appropriate for an outdoor installation, even if it's in conduit. You will need to use something outdoor rated, either a UF cable or individual outdoor-rated conductors.

Finally, 500 feet is a very long run. Make sure you plan carefully. Even simply buying cable that long will probably require getting a whole spool. And pulling the cable through conduit is a whole other challenge.

At this length you might consider using aluminum cable, which is somewhat cheaper for large sizes, although it definitely complicates the installation. I don't know much about aluminum wiring but I believe it requires special connections and the wire amp ratings are different.

Since you are already going to be using an electrician, I think you should ask him/her what they recommend.

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  • Aluminum will be fine with a real electrician to manage the connections, and will cost a LOT less than copper at the current price differential, even though it needs to be a larger size for the same voltage drop. 2/0 or 3/0 to keep it under 3% drop @ 50A (2/0 at 450 ft, 3/0 for 500.) 1 or 1/0 copper for the same run/percentage drop. electrician2.com/calculators/vd_calculator.html
    – Ecnerwal
    Commented Jun 24, 2015 at 22:40
  • Aluminum wire is less conductive, so you'll use larger conductors than copper. Typically it's only one size larger, so in your example case it would be #1 AL instead of #2 CU. You'll also have to use AL rated connectors, and sometimes oxide inhibitors as well. Though the OP says an Electrician will handle the hookup, so you won't have to worry about that.
    – Tester101
    Commented Jun 24, 2015 at 22:42
  • I advise against mixed metals. Use Copper. Can you park the thing closer? Dang 500' is long run.
    – Trout
    Commented Jun 24, 2015 at 23:56
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    @Trout - Why? It was my understanding that with appropriate modern connectors, AL wire is as safe as copper.
    – Johnny
    Commented Jun 25, 2015 at 0:19
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    @Trout You're not mixing metals. You run AL from breaker to receptacle, no mixing involved.
    – Tester101
    Commented Jun 25, 2015 at 2:16
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You will need FOUR conductors.

A 50A RV circuit/receptacle is a 120/240V circuit which requires two hots, a neutral and a ground. Regardless of what you use, 6/2 would NOT be appropriate.

I also agree, 500' is a LONG way for 120/240V. Not the best situation.

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