Need to Install a 50 Amp Circuit from Workshop for Motor Home

[Dennis McDonaugh]

I have a parking pad next to my workshop that I had put in for our 5th wheel. The 5th wheel only had 30 amp service so I just ran a large extension cord from the workshop to the plug for the 5th wheel. We're buying a motorhome with 50 amp service and I want to install a receptacle box on the outside wall of the workshop. I have room in the breaker box and a ready made RV receptacle box from Home Depot. What gauge wire should I run to the receptacle from the breaker? I've looked and it looks like it has to be 6 gauge, but I want to make sure.

[David L Morse]

What are you planning to do in that RV parked next to your shop that will require 50A?

[Tom M King]

I have one on the outside our barn. If yours is a state that allows individuals to buy from specialized electrical suppliers, you can buy the wire by the foot for about half what the big box stores sell it for. If you know where the main sewer drain line is, and is somewhere downhill from the parking space, it's not that hard to add a spot to hook the hose up from the RV. It makes a good guest "cottage", and saves time on a trip not to have to find a dumping station. My drain goes about 75' before it gets to the line going to the septic tank. I ran 4", and the inlet is just an elbow with a cleanout plug. That's a pretty long run, but I just let the water run a while after draining the tanks, and have never had to snake the line.

[Mike Heidrick]

I have a parking pad next to my workshop that I had put in for our 5th wheel. The 5th wheel only had 30 amp service so I just ran a large extension cord from the workshop to the plug for the 5th wheel. We're buying a motorhome with 50 amp service and I want to install a receptacle box on the outside wall of the workshop. I have room in the breaker box and a ready made RV receptacle box from Home Depot. What gauge wire should I run to the receptacle from the breaker? I've looked and it looks like it has to be 6 gauge, but I want to make sure.

50 amp is 6ga

[Dennis McDonaugh]

What are you planning to do in that RV parked next to your shop that will require 50A?

The shore power connection is 50 amps and I want to be able to run both air conditioners while it's parked.

[Dennis McDonaugh]

6 gauge it is. Thanks.

[Tom Giacomo]

I ran a 75 foot line to my greenhouse to run the heaters. I used 6ga but the big box stores here did not have a 50 amp breaker I had to go to a electrical supply house to get it.

[Ole Anderson]

If your wire is rated for 75 degrees C which MOST is you can use 8 ga copper. A long run of course begs a fatter wire.

I finally brought my NEC book up from my shop to now sit beside my computer for exactly these questions. Ampacity tables 310.16.

[Dennis McDonaugh]

If your wire is rated for 75 degrees C which MOST is you can use 8 ga copper. A long run of course begs a fatter wire.

I finally brought my NEC book up from my shop to now sit beside my computer for exactly these questions. Ampacity tables 310.16.

The run from the breaker box to the receptacle will be less than 50 feet. I can use 8 gauge for that distance?

[Ole Anderson]

I would. You will probably never be actually drawing 50 amps for any period of time unless you have an electric dryer in your new MH. Most likely never more than 30 amps each leg which is twice the juice you get from your 30 amp 110 volt plug. Are you just putting in a 50 amp plug? Remember if you do a 30 amp RV plug too, it must be wired for 110 volts. Electricians have wired many as a dryer circuit at 220 volts and the result is fried everything in the rig.

[John Lankers]

Dennis, I don't think it's cut and dry. You're saying less than 50', don't forget to add the 25' cable from the RV to your plug in.
The other issue is the 50 Amp service itself, you have two legs capable of handling 50 Amp each, which is a total of 100 Amp @ 120 Volt. Let's say you run 2 AC's at 15 Amp each (maybe 20 at startup) you have to have the water heater on @ 12 Amp, the charge controller at 4 - 12 Amp (depending on the model), washer/dryer 25 Amp combined, microwave @ 12 Amp, oven @ ...no wait. You see where I'm going with this, we have a 5th wheel with all the above where I installed Amp meters on both legs and never even come close to 50 Amp. You might be okay even with 8 awg wiring and a 30 Amp breaker, but you will never reach 40.
If your RV has EMS it can be programmed in a way that the inverter takes some of the overload ie. when both AC's start at the same time, or the microwave.

[David C. Roseman]

Aren't we over-complicating this for the sake of the price difference between 6ga and 8ga cable? :confused: The run is less than 50' to a 50amp breaker box that the OP's already bought. Sure, Dennis is unlikely ever to draw 50amps, but if he goes ahead and uses 6ga, he'll never worry about it.

[Rollie Meyers]

If NM "Romex®" cable is used then 6 AWG has to be used for 50A, if conduit is the wiring method then 8 AWG THHN/ THWN can be used for 50A. The reason 6 AWG w/ NM cable is that the 60 degree ampacity has to be used even though modern NM cable is 90 degree rated, per NEC article 334.80. NM-B denotes 90 degree cable.

[Dennis McDonaugh]

I would. You will probably never be actually drawing 50 amps for any period of time unless you have an electric dryer in your new MH. Most likely never more than 30 amps each leg which is twice the juice you get from your 30 amp 110 volt plug. Are you just putting in a 50 amp plug? Remember if you do a 30 amp RV plug too, it must be wired for 110 volts. Electricians have wired many as a dryer circuit at 220 volts and the result is fried everything in the rig.

I don't think it will ever draw 50 amps, but that's the connection the motor home comes with. My last RV had 30 amp service, but I always plugged it into a 20 amp circuit and never tripped the breaker.

[Dennis McDonaugh]

Dennis, I don't think it's cut and dry. You're saying less than 50', don't forget to add the 25' cable from the RV to your plug in.
The other issue is the 50 Amp service itself, you have two legs capable of handling 50 Amp each, which is a total of 100 Amp @ 120 Volt. Let's say you run 2 AC's at 15 Amp each (maybe 20 at startup) you have to have the water heater on @ 12 Amp, the charge controller at 4 - 12 Amp (depending on the model), washer/dryer 25 Amp combined, microwave @ 12 Amp, oven @ ...no wait. You see where I'm going with this, we have a 5th wheel with all the above where I installed Amp meters on both legs and never even come close to 50 Amp. You might be okay even with 8 awg wiring and a 30 Amp breaker, but you will never reach 40.
If your RV has EMS it can be programmed in a way that the inverter takes some of the overload ie. when both AC's start at the same time, or the microwave.

John, I have considered just running 8 gauge and a 40 amp breaker to the "50 amp" receptacle for that very reason. I'm not likely to even draw that much current.

[Dennis McDonaugh]

Aren't we over-complicating this for the sake of the price difference between 6ga and 8ga cable? :confused: The run is less than 50' to a 50amp breaker box that the OP's already bought. Sure, Dennis is unlikely ever to draw 50amps, but if he goes ahead and uses 6ga, he'll never worry about it.

That's what I'm thinking David. I'd rather do it once and not have to think about it again.

[Dan Henry]

I ran 8 3 wire and used a 40 amp breaker and has worked great. Look at the RV breaker box you can get a feel on witch units are on each line. every other breaker are on the same line, addup the amps and you have idea on the amperage on each line.

dan

[Dennis McDonaugh]

I ended up buying a 50' roll of 6 gauge from Lowes. I haven't connected it to the breaker box or installed the outlet yet. That wire is stiff!

[Dennis McDonaugh]

Now that I have the 50 amp breaker installed in the box and the 6 gauge wire run to the location of the receptacle, I'm having second thoughts. I bought a single 50 amp receptacle box and now am wondering if I shouldn't install one of those boxes that has a 50 and 30 amp RV outlet plus two normal 120 outlets. They also have breakers in the box for each circuit. I think I can return the box I bought which was less than $30 and order the larger box. I'm assuming it would only need the one line.

[Ole Anderson]

Unless you get a TT with only a 30 amp outlet, your 50 amp connection is all you ever need for a 5er or MH. Now if you need a standard receptacle for other uses that is another thing altogether. I would stick with what you have.