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Wire Size For 50 Amp Receptacle

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I have a 30 amp motorhome and I want to install a receptacle in my garage 85 feet from breaker box. I plan on purchasing a newer MH in the future so I want to install a 50 amp receptacle.

It's 85 feet from breaker to receptacle and 25 feet to motorhome. 50 amp power cords on motorhomes are typically 6/3 + 8/1 ground. The chart for electrical wire size says #4 for lengths over 100’.

http://www.myrv.us/electric/

Is there any reason to use greater than #6 considering the MH power cord size?

Is the distance of the MH power cord figured into the distance to determine wire size?

Would #6 wire be sufficient?

It seems to me running #4 wire 85’ through the attic only to have #6 for the last 25 feet would defeat the purpose of using #4.

Thanks

Charlie

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It is very doubtful that you will use a full 50 amps on each leg of the circuit; therefore, three #6 wres with a #8 ground will work very well. My 50 amp outlet is wired with #10, but the circuit breaker is 30 amp in the main panel of the house. I could never run 50 amps on either leg, but I am able to run all my appliances and both air conditioners without any problems of over heating or voltage drop. Actual maximum current I have had is 24 amps on one leg and 18 on the other. In your application, you will be safe, and the breaker will protect your wiring.

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Counter-point. The extra cost of wire is not huge and cost of labor is the same. And, yes, the longer the wire run, the larger the gauge needed.

Predicting your electrical needs a coach or two in the future may not be worth it. As an example, your next or 2nd coach may be all electric and you may choose to use it as a guest house when family/company visits.

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While this is not really my area of expertise, I would seriously consider consulting a local electrician, doing the right thing the first time and not having any regrets about what you have done down the road. I would much rather have some wires that were too big for the job than even one wire that was too small.

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It won't hurt to consult an electrician as Bill mentions. I believe you will find that if you run #4 wire to the garage you will have full strength 50A service at that point. Then using #6 wire for the final 25 feet to the motor home satisfies the requirement to keep the #6 wire under 100 feet. After all, the 50A service at a campground post has come a great distance, hopefully in #4 or better wire. You still use the #6 wire in your coach for the final 25 or 30 feet.

It is true that you may never use the full 50A at any time but you never know. Also, when you sell your home, alternate wiring schemes will be caught by the inspection required in most locations. At that time you will have to correct the wiring in order to sell the house. You might was well have it done properly so you get to enjoy using the proper wiring rather than having to correct it only to sell the house. Besides, you'll sleep better at night. No worries!

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Thanks for the replies. Much appreciated. After taking some exact measurements It will be a 79 foot run from service entrance panel to receptacle. I talked with an electrician at work who does home inspections. He said #6 was sufficient. Tomorrow I have a telephone appointment with the city inspector to determine the correct type of wire and conduit to use.

BTW. #4/3 w/g is more than double the cost of #6/3 w/g.

Thanks again

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If cost is not much more, run the larger wire and install a sub panel for more options later.

Good advice but I don't need a sub panel, just a RV outlet.

After talking with inspector and electrican I will go with 6/3 wg NM-B #4 is overkill and not needed for this application. Lowes has a $20 off coupon good starting 9/17/12. I plan on doing it myself and having it inspected by an electrician when done. Right now I have a 30 amp coach and maybe in future a 50 amp.

Thanks again for advice.

Charlie

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It would be a good idea to add a disconnect before the outlet. You can use one like those used for a hot tub or airconditioner. By using this to "turn off" your circuit at the outlet, you would not be plugging in or unplugging hot which will eliminate arcing and pitting of your motor home plug.

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And while you have the trench dug it is a good time to add

Water Line

Internet Cat 6 Cable

Coaxial cable (for cable TV or Satellite)

Telephone line

John

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