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Electrical Wiring in the Home/Wiring a supply outlet to my motorhome


QUESTION: Can you give me a wiring schematic to show how to connect my 4 prong 50 amp 120 volt shore power cord from my motorhome to a 4 prong 50 amp receptacle on my house?   Specifically, how do I get a 4 prong receptacle wired into my house's breaker panel using a 4 wire cable (with ground wire, bare AWG 10) and a green, a red, a black, and a white wire (AWG 6) that are connected to my 50 amp receptacle as follows?     The top center prong is a Ground (green wire),  The two outside prongs are connected to the red and black wires respectively (there is NO voltage - ZERO volts - between them).  The bottom (center) prong is connected to the white wire.  There IS 120 volts between either of ONE of the side prongs (the red or the black wire connections) and the bottom center prong (the white connection).
Apparently the motorhome only gets 120 v. single phase power. How do I wire that from my circuit breaker panel to the 4 prong outlet?   

Any help would be greatly appreciated!

Thanks,  Art

ANSWER: Art  well you have 6 wire and 50 amps   115 is possible,   NOT PROBABLE    should be documentation somewhere or give me the info on the motorhome  and I will look          are you sure you have 120 from black or red to neutral ?   but not 220 between them?   That hardly seems possible,      that would mean the red and black are the same phase or wire        doesnt seem right to me,    not arguing you measured it   so I have to take what you saw as the truth   are you sure there is not a bad breaker or fuse or something somewhere ?

I would like you to retest and find some info on that motorhome     again if you give me the motorhome data I will look it up with you,   it bothers me even with 6 wire and 50 amps  that you get 120 or 115 twice  but no 220     see what I mean  ?    One should be from one pole and the other from the other pole  the breaker is it is a double pole breaker ?

Please check again    I would think only 30 amp would be 120    50 should be 120/240   below is the connections but somehow someway  maybe by design they only gave you 120  but it seems odd   please let me know before proceeding  and here are the diagrams:

---------- FOLLOW-UP ----------

QUESTION: Thank you very very much, Will, for all the info you sent me.  And your questioning and your input too!

The info is very helpful.   I have had electrical problems with this motorhome ever since I bought it (used)!  The previous owner must have thought of himself as an "electrician" because he had extra wires running all over the place.  He also changed out the generator and put in a larger capacity one and bypassed the automatic change-over switch so I have to MANUALLY plug the 50a power cord into the generator OR shore power outlet.  (I wonder why?)

I am going to have to do a lot more investigating on the wiring in the coach.  I did not know that 50a shore power was supplied as 120/240, since my generator only supplies 120v single phase.  Yet I am able to run everything in the coach AND TWO air conditioners without dragging down my generator! ??

Thanks again.   I'll be getting back to you when I can find out more about the wiring in my coach.

Onan Generator
Mod # 6.5NHDFB 1M
S/N L010311179
Volts 120/240
Amps 27.1
KVA 6.5
PH 1
Options: R 104-2 C162 NHD

This is all I have. I have no instruction manual, or diagrams. They were stolen on a break-in! (Can you believe that!) Nuts.


Art  I can believe the break in,    had one myself,   kid   they caught him  but the weird stuff he took I never got back,  

Anyway you say your generator only supplies 120  but the ONAN above says 120/240    

SO I am surprised by that       

OK  on the power thing   as you say you run a lot of "stuff" off 120.   

Here is how that all works,     most people think they save money if they use 220 versus 120 on say a swimming pool pump.

Well maybe upfront a little because you can use smaller wire to get to the pump, and any other switches and so on don't have to handle the higher current of 120     but in reality   after that there are no savings,       this is why    power is power,    

motor same HP   220 volts   10 amps      v  x  a =  watts  [power]

motor same HP   110 volts   20 amps      v  x  a =  watts  [power]

so if you do the math on either    it comes out the same    

That is why they can shoot 100,000s of thousands of volts down the country side on a wire the size of your little finger,     but the lower the voltage by transformation    the higher the amps     so all you do with higher voltage is lessen wire size and current capacity on devices in the circuit,   it has NOTHING to do with power,     

What he might have done,  not knowing any better is somehow  [I and I couldn't tell you how,    split up the  two 110 circuits off ONE POLE  or one HUGE main breaker,   not a good thing to do,  cause you get into all kinds of neutral issues  or could,    

So say he did not use two poles or two breakers  [a double pole breaker]  and somehow used one 50 amp single pole breaker,   it is physically possible to get two circuits off that, but the hot is the same hot for both  if they are split out in the motorhome,    that would mean you would have to kill the main breaker to kill any sub breaker     not safe   

It would be like running two extension cords to the motorhome,  in one bundle      see the problems?

That also probably explains why the auto transfer switch is not in use because it would want two poles   or two hots,     and then transfer them as two circuits   but with just one hot  although it might be a big ole wire   it is back to the two extension cords    and I bet that is just what you have,     

The possible good news,  is   at the main on the motorhome  it should not be difficult to divide the circuits into a main and then two individual circuits or four or whatever   three 15s    however it was designed,       

Where you plugging the existing plug into a 240 trailer park outlet  ?

If he opened  one  hot   at the receptacle   then you would get nothing but one hot  and neutral to your motorhome  which if you had enough wire size   [again like two extension cords] you could run whatever,  up to that limit, of current,     but that is a bad way to do things

Without seeing it I would be hard pressed to say that is exactly what he did but I bet he just did not know how to split out 240    and made it  "simple"  by  using it like an extension cord,        

I would do exactly as you described,   find out how that motorhome is wired,  and get it back to a main so it is Hoyle,   I see too many dangers running one circuit/one hot one extension cord and 50 amps of 120   

You should not have to gut the motorhome   as most things are 120,  but it would allow for smaller wire to the motorhome, and use of an auto switch        

Here is another not often thought through problem       many home outlets wear out,  from having cords plugged in and out,      then the clamping power of the outlet gets weak,  

With all the modern day electronics,  these loose connections cause ripples and trash down your outlets to the TVs and whatevers     and that causes all kinds of bad pictures snow, bad sound,  it makes and breaks in tiny arcs not visible   and is a major source of problems with modern day electronics  where no one has replaced the old outlets       

Even if you have to take it to a motorhome service center  I think it would be the right and safe thing to do, not only that but if you keep the existing plugs  you are going to have to make up some kind of funky plug configuration at your home,   which means one big 50 amp breaker using huge wire       

Then I don't understand why you say your generator only puts out 120 when the data plate says 120/240   is that more of his handywork?

I went through a house fire,   believe it or not a coffee maker cord shorted out right in the middle,      we dont use it much  but I firmly believe we had a surge that caused that problem not a worn cord,  it looked like new,      but you want NO PART OF A HOUSE FIRE  ON WHEELS OR NOT ON WHEELS      it is HELL LIKE YOU WOULD NOT BELIEVE       I guess if an individual sells the motorhome they can get away with this kind of thing, but if it is a licensed dealer they have to follow code,  NEC  cuts off  120 only at 30 amps   for a reason     

I know you don't want to hear that and maybe someone at a service center can figure something out to use the existing,  but I would sure try to get it back to being right and stop the plugging and unplugging  because that is going to wear out over time,    it can also cause a high resistance connection when it becomes loose and that creates HEAT   and low voltage    it may take a while or it might not    but it will get loose   sometime,    

You can use my private email at the bottom  and it is much faster for me to walk you through this    between the two of us we should be able to get it right without costing an arm and a leg   and then you are good to go  the right way,    

I also fix generators  so if it is labeled 120/240  there is a way to put it back,   he didnt have it rewound   so I know there is a dividing point in that genset  somewhere    

Let me know after you look around and we can decide further         keep me in the loop and I will do my best to keep anyone from ripping you off any further and get it right and safe  
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Will Babbitt


Electrical issues of all types, wiring, control, appliances, components, specialty in Electric MOTOR or APPARATUS trouble shooting, electric motors, electrical problems, single phase, three phase, DC, capacitors, elevator MG-Sets, modifications, reverse engineering, VFD Drives, single to three phase convertors. Repair of most any electrical/mechanical/electronic apparatus, OEM, AC, DC, Industrial Applications, Three phase, single phase failure mode, determining the root cause of the equipment failure BEFORE failure repeats, Antique appliances, electric motors, fans, ceiling fans, base mount fans, poor equipment performance, Modifications, habitual failures, vibration, redesign, obsolete issues, collectible items restored, rewinding. Owner of EMR Repair Inc More information on electric motors, under Engineering/Motors Ask about any electrical or mechanical problems in the home, office, or even at your work. B2B or business to business CONSULTING I can do but it would be a much more complex issue, that would require a significant amount of time. from there we can discuss and begin work on about anything. Industrial electric motors, controls, troubleshooting, vibration, alignment, any type of industrial or commercial electric/electrcical equipment For the home owner, renter, apartment if you have odd things going on, describe to me, photos are normally very helpful, appliances, heating and air conditioning issues, light switches, installation, DIY PROJECTS FOR THOSE NOT EDUCATED IN ELECTRICAL, we can do some things, but for safety and sanity reasons, I may refer you to a local electrician, and help you find one, help you with pricing and even speak directly with anyone you hire if you have issues,


Over thirty years with a major repair and sales company, VP of Operations, and former owner of my own specialty repair shops, MEAR Services local to Kansas City Missouri EMR Repair Inc., located in Kansas City Missouri, 2014 sold both businesses to JCI Industries, Lee's Summit Missouri Evaluation and repair of electrical/mechanical apparatus. Electrical and mechanical repairs, trouble shooting including, vibration and balance issues. provides this service, and the huge costs to provide help on about any subject. They provide the servers, the people to vet the experts, costs that would be the same as operating a good sized business, They should be appreciated for what they do, the huge costs and the great help they provide for free, Electric motor questions, can be answered here but there is a dedicated category that has other experts to help and add to a solution. Other common questions, are noises in the walls, breakers tripping, devices not starting or shutting down for no apparent reason, smoke alarms buzzing, thermostat change outs, or sizing wire or needing information for a new project, but anything can be resolved, anything, with enough effort and patience, DIY, with electrical is possible, but in most cases the use of a simple ohm meter or volt meter is needed, they can be purchased at any hardware store for a few bucks. If you have smoke, or smell smoke, don't be writing me, call 911 the Fire Department has no problem looking for smoke smells, better then spraying water on a blazing fire. DO NOT GET CAUGHT INVESTIGATING AND TRAPPED IN A BASEMENT LOOKING FOR A BLOWER FAILING< As to the tip jar, it is up to you, it is appreciated, every expert spends out of pocket that I know, we spend on IP time, computer wear, printing documents, books, and of course our time, but if we prevent a $400 service call, we did well,

Former IBEW, EASA, IEEE, UL, ..............


10 plus years, various Technical Schools, followed by Industrial College Credit and non Credit Courses, electronics courses, experience in most any electrical apparatus, electric motors and generators, AC OR DC, fractional to above 5000HP, other electrical apparatus, slip rings, sleeve [plain] bearings, lubrication, identification-no data plate, control components, service and sales. I have continued night schools for decades, the list is extensive. I have been in the business of repairing most anything with wires or mechanical parts for decades, I have some helpful hints and directions you won't have to dig up. Or hopefully not have to pay a huge service call invoice to find.

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