Can someone help with wiring recepticle for shore power

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Can someone help with wiring recepticle for shore power

October 29, 2012, 07:36:56 pm

I am going to run wire and install outlet near my motorhome to run heat rather than winterizing. My question is
motorhome has 3 prong twistlock at the other end of the cable that hooks in receptacle has 4 studs. Also the cable has 4 wires red, white black and green.
My question is why are there 4 wires when the plug on MH end only has 3 prongs. Also I will be buring this cable in PVC, is SO cable better than Romex or should I use romex?
Thanks everyone for your input.

Re: Can someone help with wiring recepticle for shore power

Reply #1 – October 29, 2012, 08:51:55 pm

If you put your coach details (year, model, etc.) in your signature it will help us try to fill in the blanks.
Chances are your 1999 U-270 coach has a 50 amp Marinco connector like the one shown below. The three prongs are as follows; two of them are 120VAC each, the other one is the neutral, the ground is obtained via the large contact on the side of the connector as shown.
See attachments for details.
Make sure your electrician understands RV electrical systems.
If you heat with electric vs. propane? you will need to provide heat in the water bays. With propane, the rear furnace diverts some heated air into the water bays.
Good luck,

Re: Can someone help with wiring recepticle for shore power

Reply #2 – October 29, 2012, 08:55:55 pm

The power cord has 4 #6 wires. The red and black are the phase conductors, the white is the neutral, and the green is ground. All 4 wires are connected to the plug. The metal ring is connected to the green (ground) wire. If you were to put a volt meter across the wires you wil get 120V between either the red and whte, or the black and white. If you go between the red and black you will get 240 volts. The voltage between the green and white is 0 (zero)

The receptical you will need is a 50A 10/240V 4 wire plug. If you run romex it needs to be "UF" to be run outside or underground.

Re: Can someone help with wiring recepticle for shore power

Reply #3 – October 29, 2012, 09:35:11 pm

You are probably better off running THHN (separate wire in conduit). you will need 4 wires 2 hot 1 ground and one common. You should use a separate disconnect or breaker I think it requires #8 wire.

Re: Can someone help with wiring recepticle for shore power

Reply #4 – October 29, 2012, 09:47:00 pm

As to the THHN (separate wire in conduit). Do you recommend this rather than the SO cable. Also should I have a breaker at the outlet and in the panel box?

Re: Can someone help with wiring recepticle for shore power

Reply #5 – October 29, 2012, 09:50:26 pm

Ho long is your cable run? That can change the recommendation for wire size...

Re: Can someone help with wiring recepticle for shore power

Reply #6 – October 29, 2012, 10:02:12 pm

72 ft.

Re: Can someone help with wiring recepticle for shore power

Reply #7 – October 29, 2012, 10:20:16 pm

Rick's photographs and documents on RV wiring safety are excellent documents to help with your project. Be sure you and your electrician understand the specific requirements for your RV. An error could be costly and dangerous.

I used four 6-gauge copper wires about four feet long running from a 50A breaker pair in the entrance panel to hook to a socket in a box designed for outside service. I ran the wires through 3/4" flexible conduit. If you use 3/4" flexible conduit, put the wires in the conduit BEFORE you put the connections fixtures on the conduit. It is a tight fit.

I use the 25' cord that attaches to the coach, and a 25' extension cord designed to extend a 50A RV connection. We have good voltage in the coach even with both air conditioners running. We have excellent voltage at the entrance panel. About 54' of 6-gauge copper wire with two connections along the path works for our situation. Don't know how well about 72' or 72' plus a 25' cord on the coach would work if you put a significant load on the circuit.

My understanding is that all of the wires for a 50A hookup should be at least 6-gauge. If you are running the wires more than 50' from a service panel, it may require larger wire. Check with a qualified electrician who understands what you plan, and who understands the requirements for your RV.

Distance makes a difference. We were in a COE park in the summer hooked to a 30A supply. We were running one air conditioner. Voltage was 106V. I considered it unacceptable to run our appliances at that voltage. We moved closer to the electrical distribution panel and the voltage was 115V with one air conditioner running. In the heat of the day (106F) we ran the generator in order to run both air conditioners.

Re: Can someone help with wiring recepticle for shore power

Reply #8 – October 30, 2012, 08:27:37 am

Having a breaker at the outlet is convenient to turn it on and off as you plug in and out. You may want to have a 2nd 110 outlet for misc. utility needs as well. I think # 6 wire is going to work better with the 72' run. As for the SO cable, it is normally run naked and the THHN would be in conduit. Some of the RV boxes are available with breakers, 110/20 amp, and the 50 amp plug.

Re: Can someone help with wiring recepticle for shore power

Reply #9 – October 30, 2012, 09:10:58 am

Howdy green99,

Here's a link to some useful RV Electrical information: RV Electric

Good Luck, Dave A

Re: Can someone help with wiring recepticle for shore power

Reply #10 – October 30, 2012, 12:13:15 pm

What Turbojack said that is correct:
If you were to put a volt meter across the wires you wil get 120V between either the red and whte, or the black and white. The voltage between the green and white is 0 (zero).

What Turbojack said that is not correct:
If you go between the red and black you will get 240 volts.

The voltage between the black and red, which are both "hots" will depend on the phasing of the two hot supplies. If the black and red hots are out of phase (like the input to my house) you will, indeed, see 240 volts between black and red. If however, they are in phase (like the black and red from virtually all Foretravel installed generators) you will see zero volts between black and red. From blogs I have read, I deduce that few campground provide 240 volts between black and red.

The reason that Foretravel installed generators have zero volts between back and red is "load balancing". It would be a simple wiring change at the generator junction box to convert the supply to provide 240 volts at the panel, however it would not be a good thing to do.

The reason that campgrounds seldom provide 240 volts is the installation costs (and perhaps damger). Providing 240 volts to motorhomes is much more costly then providing 120 volts.

Do not worry about plugging 240 volts into your motorhome, our Foretravels will accommodate it safely, and unless you check, you will not even know.

Anyone wanting more details about why, just ask - I am known for providing endless details.

Re: Can someone help with wiring recepticle for shore power

Reply #11 – October 30, 2012, 08:39:10 pm

Quote from: P. Wyatt Sabourin – October 30, 2012, 12:13:15 pm

......................................................What Turbojack said that is not correct:
If you go between the red and black you will get 240 volts................................................

Wyatt,
If an RV 50A power plug is wired correctly in the USA, according to the National Electrical Code, the voltage between "X and Y" or "BLACK and RED" will be 240 AC and the power available will be (nominally) 12,000 Watts.

Some Campgrounds advertise 50-amp Electric Service but in reality they misrepresent what they offer. A TRUE 50-amp Service is 120/240 Volt. In this Service the HOT leads (X & Y) come from L1 and L2 so when you check it the voltage between X and Y should be 240-Volt, X and W 120-Volt, Y and W 120-Volt, X and G 120-volt, Y and G 120-volt, W and G 0-Volt. This service provides 12,000 watts.

On a FAKE 50-amp they use L1 or L2 for BOTH side (X & Y) of the HOT leads therefore the voltage between X and Y will be 0-Volt, X and W 120-Volt, Y and W 120-Volt, X and G 120-volt, Y and G 120-volt, W and G 0-Volt. This service will give you 6,000 watts. It is better than 30-amp with 3,600 watts but it is NOT a TRUE or CORRECTLY WIRED 50-amp service.

Sorry to contradict, but this could be confusing to a lot of the Forum, if it wasn't elaborated upon.
V/R,
Neal

Re: Can someone help with wiring recepticle for shore power

Reply #12 – October 30, 2012, 08:55:57 pm

If properly load balanced a 240 volt service will show very little current flow in the neutral. It seems that two in phase 120 volt lines as service will show the total amperage of the two lines flowing through the neutral-a potentially very big problem unless your neutral line is rated to carry double the current of your hots. Since this is essentially how the generators are wired I assume provisions were made for this unusual situation. If so, either situation would work but four wire 240 bolt service certainly seems like the way to go.

Chuck

Re: Can someone help with wiring recepticle for shore power

Reply #13 – October 30, 2012, 10:49:23 pm

I have not been in as many campgrounds as others on here but the ones I have gone to if it has a 50A plug there has always been a 50A double pole breaker, thus 240V between the phases. The 30A plug is a 120V plug that has a single 30 amp breaker. As has been mentioned above when you have 240 volts the neutral wire only carries the unbalance between the 2 phases. Say your rv is plugged into a 50 A 240v plug. All of your appliances on your RV are 120V If you have both AC's running if one was bigger then the other one load conductor would have say 15 amps on it, with the other say having 13 amps, the neutral would have the difference of 2 amps on it.

If each phase conductor of a 50A plug would be on the same phase then the neutral would have the sum of both of them so in the example above the neutral would have a load of 28 amps. If the load on the neutral wire goes over the capacity of #6 wire longer then a short time, something is going to burn up.

I have not checked how my 10,000 W generator is wired but if it only puts out 120V then it is putting out aprox 83 amps at 120V. If this is the case then it should have a neutral wire rated to carry the 83 amps from the generator to the neutral bar of the breaker box. I will check when I go back out to it.

Re: Can someone help with wiring recepticle for shore power

Reply #14 – October 30, 2012, 11:02:18 pm

Quote from: turbojack – October 30, 2012, 10:49:23 pm

I have not been in as many campgrounds as others on here but the ones I have gone to if it has a 50A plug there has always been a 50A double pole breaker, thus 240V between the phases.

That's actually an assumption (the 240V between phases). Often the case, but best to confirm, especially in an older campground.

-M

Re: Can someone help with wiring recepticle for shore power

Reply #15 – October 30, 2012, 11:42:49 pm

Neil, sorry, I do not agree with you.
The number of kilowatts of power available with 50 amp service is not different if you messure zero volts between the red hot and the black hot or if you message 240 volts. There is no difference in kilowatts available, and that is not my point. My point was, if you measure zero volts between hots it does not mean you have less kilowatts available to your motorhome and you do not need to be concerned about it. Sorry, I am a real professional engineer, you cannot wow me with numbers.

Chuck Pearson, Thank you for your comment:
You are exactly right about being concerned about the amount of current that the neutral wire is carrying.

Torbojack, you are exactly correct:
The neutral wire with Foretravel installed generators may carry 83 amps, however my 1996 was wired sized for 60 amps while the automatic selector switch has a capacity of only 50 amps -- ooppps. The automatic selector switch which I remove had a discoloured neutral connector which I believe was caused by "OVERLOaD".

Foretravel is a great coach, probably the best that can be purchased, but they are not perfect.

I am still contemplating about what to do with the under sized neutral wire from the generator, stay tuned for my solution.

Do not misconstrue the message here, I love my foretravel and plan to drive it for the next 15 years while I perfect it. It is not perfect now, however, it will be in the future.

Re: Can someone help with wiring recepticle for shore power

Reply #16 – October 31, 2012, 12:34:54 am

Quote from: P. Wyatt Sabourin – October 30, 2012, 11:42:49 pm

...................................My point was, if you measure zero volts between hots it does not mean you have less kilowatts available to your motorhome and you do not need to be concerned about it. Sorry, I am a real professional engineer, you cannot wow me with numbers.........................

Wyatt, 6K or 12K available watts all depends upon how the campground failed to meet the code.
In the hundreds of campgrounds we've stayed in, I've only seen 0 Vdc between X and Y four (4) times. In each case, being a licensed engineer (and more than just a little persnickety) myself, I asked them to check the pedestal. One just moved me to another site. One refused to check the breaker, and the other two sent electricians. On both of those occasions, although a double pole, double throw TOL breaker was installed, the outputs were tied together and only one phase was connected to one input pole. Now whether that was by campground malfeasance (One told me "You pay for 50 amps, you get 50 amps -- not 100") or by campground/electrician ignorance I can't say. But in my limited population of two verified cases out of hundreds of samples, the watts available were 6,000, not 12,000.
Just sayin', if it isn't wired IAW NEC code, it is worth investigating why. Maybe local code intentionally deviates from National code, but much more likely -- something is wrong with the campground intent or technician knowledge or both.

V/R,
Neal

Re: Can someone help with wiring recepticle for shore power

Reply #17 – October 31, 2012, 12:54:38 am

Neil:
Thanks for your input, sounds like we are on the same page.
I love this Forum because I learn something everyday.
I had no idea that campgrounds were playing these games with their unaware clients.

I also have had confrontations with campground staff over A/C power and been looking at a "blank stare" because they had no understanding what I was talking about.

Re: Can someone help with wiring recepticle for shore power

Reply #18 – October 31, 2012, 09:04:22 pm

I could see a campground wired by someone that did not have a clue as to the correct way. If it never got inspected it would be possible no one would know unless they have a meter that would show if they had 120 or 240V as in some of the big coach buses. Or they tripped a breaker.

When ever I go to a campground now I will pull out my meter to check the voltage.

Re: Can someone help with wiring recepticle for shore power

Reply #19 – November 04, 2012, 01:37:45 pm

I added a 30 amp drop (Bought a electrical box from Lowes) from my outside breaker box to where the RV is parked for the same reason (heating, cooling and charging). As on AC unit will do, I went with 30 as 30 amps times 120 volts equals 3,600 watts and the AC unit is around 2500 watts.

The Lowes guy was very helpful with the breaker and wire that I needed. It has been working successfully now for 3 years.

Re: Can someone help with wiring recepticle for shore power

Reply #20 – November 04, 2012, 07:53:29 pm

Don't forget you will have your fridge on and the battery charger and the converter to run the lights. You will be able to run a lot on 30 amp but if you have the capacity do 50 then I would do that.

Re: Can someone help with wiring recepticle for shore power

Reply #21 – November 07, 2012, 11:18:54 am

Thank you all for your input. I have it wired and ready to go.
I would also like ask, what is the best way to insure that campground plug is wired correctly?
I just always assumed it would be, all help is appreciated.
I am new to the FT's and this site, I want to say thaks to everyone for their help.
Jerry

Re: Can someone help with wiring recepticle for shore power

Reply #22 – November 07, 2012, 11:53:51 am

Jerry,

Several of us use something like this, Not lots of $$ to build, simple to use & build, could save big $$$

http://www.foreforums.com/index.php?topic=12050.msg62032#msg62032

Pamela & Mike

Re: Can someone help with wiring recepticle for shore power

Reply #23 – November 07, 2012, 08:32:21 pm

Pam and Mike,
Thanks for the links excellent info.
Jerry

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