50 amp extended run with UF electrical cable

[Bmaintz8]

Hi, need some help...
Moving my Dutch Star to my daughter's 5 acres...
Need to bury around 200 feet of UF cable for service...
DS draws a max of 50 amps (25amps at 120 volts)...
Looking at 6/3 UF cable but confused if 6 ga is big enough...
Charts say no more than a 3% drop in voltage....
Any help is appreciated...
Bob
South Carolina

[BFlinn181]

There are many calculators for wire gauge on the internet. Be sure to measure from the power panel, not just the outside run. Also, be sure that the professional electrician that does the wiring knows RV 50 amp service is two 50 amp hot lines of 120v, not 240v. The two hot lines also need to be 180º out of phase from each other.

Furthermore, TEST the new outlet with a meter before plugging in the RV.

[Isaac-1]

I would also suggest measuring the voltage at the panel you are connecting to, I did something similar to install an outlet in the shed on the family farm where I store my coach, though my run was less than 100 ft using 6/3 UF with ground from the sub panel. With mine due to the already low voltage at the panel I get drop outs caused by low voltage detection by my Surge Guard EMS in my coach when I run higher amp appliances while also running my air conditioner, etc. For example last summer I tried running a 12 amp carpet cleaner and my roof mounted air conditioner at the same time which caused enough voltage drop for my EMS to disconnect the line power.

[powercat_ras]

I would feed a RV pedestal box, such as the Siemens TL137US Talon Temporary Power Outlet Panel with a 20, 30, and 50-Amp Receptacle Installed, with a 50 Amp 240 Volt breaker using 4/3 UF with Ground Cable at a minimum, given that you don't expect to use more than 25 amps out of each leg normally. For a 200 foot run, 3 volts AC less at the 120 volt load than at the source - worst case with 25 amp load on one leg and zero amp load on other leg of the 50 amp RV outlet.

If you can afford it go ahead and use 2/3 UF the 4/3 UF will have too much voltage drop if the amps is over 25 out of each leg, due to the long 200 feet run. Some future RV using it might use more as the feed will be capable of 50 out of each leg.

[325BH]

Originally Posted by BFlinn181

There are many calculators for wire gauge on the internet. Be sure to measure from the power panel, not just the outside run. Also, be sure that the professional electrician that does the wiring knows RV 50 amp service is two 50 amp hot lines of 120v, not 240v. The two hot lines also need to be 180º out of phase from each other.

Furthermore, TEST the new outlet with a meter before plugging in the RV.

50 amp “RV” service is nothing unique. It is regular 240/120 volt 50 amp. Same deal as in your home. The 50 amp connector (plug/receptacle) is nothing unique. The same as in homes used by ranges/cooktops.

Two 120v hot lines IS 240v. That is how it works.

[BFlinn181]

Originally Posted by 325BH

50 amp “RV” service is nothing unique. It is regular 240/120 volt 50 amp. Same deal as in your home. The 50 amp connector (plug/receptacle) is nothing unique. The same as in homes used by ranges/cooktops.

Two 120v hot lines IS 240v. That is how it works.

You are correct when it's wired properly. On a 50 amp outlet, a DIY could also hook up the two hot leads from the same side of the breaker panel, thus not providing correct power. The neutral can be the same gauge as two hot leads because the AC power is 180º out of phase.

The bigger problem comes when folks plug into a 30 amp dryer outlet. An RV 30 amp outlet is 30amp 120v, a dryer (or welder) is 30 amp 240v. Folks without an EMS have fried their RV appliances plugging into an outlet that 'looks' like RV 30 amp plug.

I'd still suggest using a professional, licensed electrician to do the wiring. Most places require an inspection also.

[325BH]

Originally Posted by Bmaintz8

Hi, need some help...
Moving my Dutch Star to my daughter's 5 acres...
Need to bury around 200 feet of UF cable for service...
DS draws a max of 50 amps (25amps at 120 volts)...
Looking at 6/3 UF cable but confused if 6 ga is big enough...
Charts say no more than a 3% drop in voltage....
Any help is appreciated...
Bob
South Carolina

If your Dutch Star is 50 amp service, it is two 120 volt hots, 50 amps each. This is standard 240/120 volt service like in your home. Nothing unique.

200 feet is a concern.

The quick answer would be between 1AWG and 4AWG... depending on how balanced the load is. In reality, 4AWG would probably be OK.

[twinboat]

Why are we even talking about 30 amp service ?

The OP asked about a 50 amp extension. Do we need to muddy the waters with 30 amp 120 volt service and old outdated dryer outlets ?

Also, to pick up 2 hots on the same leg, in a service panel, you would need 2 independent 50 amp breakers, or bust one apart, and place then apart from each other. Again, the OP has enough sense to question the wire gauge. Do you think he would split up a double pole breaker ?

Its a standard 240 volt service. There Is no RV 50 amp service.
You can NOT make a " two the same phase " 50 amp service and get 240 volts from it.

[saddlesore]

Originally Posted by twinboat

Why are we even talking about 30 amp service ?

.

Because there are Forum members that may only have a 30a or 20a RV, and may be following this thread, also it is not uncommon for a RV'r to put in a 50/30/20 wired pedestal.
Not everyone has the deep pockets to have a 50a RV....

[BFlinn181]

Originally Posted by twinboat

Why are we even talking about 30 amp service ?

I brought it up because wiring can be done in a variety of ways and it is more problematic in 30 amp RVs than 50 amp ones, but it does happen. Google 30 amp outlet and you'll find a variety of 30 amp styles, some of which look like your RV plug but will fry it. Same for 50 amp outlets, there are a variety of styles. That's why I said it's best to tell an electrician exactly what style of 50 amp service you want to be installed. I've had my 50 amp EMS fail to connect at campground pedestals that aren't wired properly.

Originally Posted by saddlesore

Because there are Forum members that may only have a 30a or 20a RV, and may be following this thread, also it is not uncommon for a RV'r to put in a 50/30/20 wired pedestal.
Not everyone has the deep pockets to have a 50a RV....

I don't necessarily believe it takes 'deep pockets' to have a 50a RV, my '98 is 50a and I don't have a high-end RV or deep pockets. The rest of the above is quite true, a search of the forum will yield horror stories of plugging into outlets that aren't configured for RV service.

[Bmaintz8]

Wow.... Thanks for all of your help...
We are a few months before we move the DS to my daughter's place...
Will need to measure the distance & see if we will have to go to the 4 ga...
I have looked at the Calculators & loss factors...
In regards to the UF cable do we need the bare ground wire which makes it 4 wires all together...
My neighbor next to me is a certified RV mechanic & does some work in the park, I'll ask him to wire it all up for me...

[Gary RVRoamer]

There are two considerations for selecting wire size: ampacity (amp load) and voltage drop. 6 gauge UF will handle 55A/wire and the voltage drop calculator I used shows about 6 drop, depending on the assumptions used. It looks like 4 gauge or even 2 gauge would be a better choice for that distance. Chances are that RV won't actually put two 50A loads on the two hot wires, so you could probably use 35-40A in your load calculations, even though there may be peak periods where it gets a bit higher. As a practical matter, wires are often sized based for 80% of peak load.


There are various tables and calculators available online to show how much voltage drop can be expected over a given length. 3%-5% is generally considered to be the max acceptable drop, assuming you start out with adequate voltage (120/240 in this case).
Here is one such:
http://www.nooutage.com/vdrop.htm

[twinboat]

For that long a run, conduit and 4 single wires may be cheaper. I believe you can use a lighter gauge in conduit then UF cable.

[vsheetz]

I would consider to run #4 THHN in conduit. In most places you can bury conduit 18", whereas direct burial is 24". That 6" at the bottom can be hard digging. UF is expensive. Include a couple pull wires for future additions. Either way it will likely be considered as a detached subpanel and require a ground rod at the pedistal/destination.