Do-It-Yourself Repairs & Basic Wiring Projects:
What Size Wire Do I Need To ....
Run a 30amp and/or 50 amp service approximately 120' from entry service to accommodate  RV motor home

By Terry Peterman, the Internet Electrician

Q:  I would like to run a 30amp and/or 50 amp service approximately 120' from entry service to accommodate  a RV motor home. 

What gauge wire should be used?

What amp breaker?

- Vince

A:  Due to the length of this run (120 feet.), to get a full 50A service at 120V, you would have to run #4 AWG copper wire to stay within acceptable voltage drop (3%). 

You would use a 50A breaker to feed this circuit. 

To get a full 30A 120V service, you would require #6 AWG copper, fed with a 30A breaker to stay within the 3% voltage drop.

If you plan to use the R.V.'s full electrical system then this is what you are going to need. 

• If you only want to have the use of the lights, and keep the battery charged, and don't need the heavy loads such as A/C or washer/dryer, etc., then you could run a smaller service that would be considerably more cost effective. Then you would use the appropriate wire size and breaker. 
• You would then need the approved adapter to plug the unit in, and would have to disable the heavy loads by unplugging them or shutting off and labeling the breakers with a note that the electrical supply is not sufficient to run the heavy electrical loads.

- Terry Peterman, the Internet Electrician