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Thread: Question about adding a 30a RV Plug

  1. Question Question about adding a 30a RV Plug

    I want to add a 30a RV plug on an outside wall so I can plug in my RV. Right on the other side of the wall is a 30a Dryer (220) plug that I don't use because I have a gas dryer. It seems the logical thing to do would be to come off this box.

    The dryer plug is an older three wire type with a Black, Red, and White wire. There is no ground to the plug. Or, is the white the ground on this type of plug, meaning the white is not neutral?

    The 30a RV recepticle has three screws which I assume are for Hot, Neutral, and Ground.

    With this recepticle, can I use one of the hot wires, ie, the "Black" for power, the "White" as neutral, and add a ground? Would this be safe?

    Or should I take the other hot wire (Red) and connect it to neutral in the main breaker box, and use this as my neutral to the RV recepticle?

  2. #2
    Join Date
    Dec 2003


    You can't extend an old 3 wire dryer circuit. In the old days the neutral was bonded to the dryer chassis for a poor man's ground. You can't use the "spare" conductor as a ground either.

    The RV receptacle is 120V, 30A so you need a 30A single-pole breaker and 10/2 cable to provide Hot, Neutral, and Ground.

    How difficult is it to run a 10/2 cable back to your panel?


  3. Default

    Hi Homer,
    Thanks for taking the time to respond to my question. It would be quite a bit of work to run the 10/2 back to the panel. Someone suggested using the old Red wire from the dryer plug as the neutral, ie change it to neutral back at the panel; is this a bad idea?

    I guess I don't really understand the difference between neutral and ground.

    It looks like extending the dryer plug would leave me with only a hot and a ground with no neutral. Is that correct?

    Also, since I don't have the neutral wire I need, what makes the extension of the three wire dryer plug unsafe?

    Sorry for the newbie questions, but I'm still learning!

  4. #4
    Join Date
    Dec 2003


    In your current setup you have two HOTs(black & red), a Neutral(white), and no ground. This is no longer permitted so it must remain as is and can't be modified/extended as per the NEC (it's grandfathered for you).

    You can't use the red as the EGC (Equipment Grounding Conductor) due to restrictions in NEC 250.119. There is no way to juggle the wire assignments around and meet the NEC requirements (see NEC 200.6 & 200.7 also).

    The Neutral conductor is a current carrying conductor that is used for 120V loads. The EGC only carries current under fault conditions in order to clear the fault (trip breaker).

    Maybe this explains why you can't really do much with that existing dryer outlet.


  5. #5


    Just curious is this an SE cable or a Romex cable? Do you have red, black, bare or red, black, white?

    Homer check out rule 250.119.B.1, by that rule if this is not SE cable but rather romex with a white wire then you could strip the red wire wherever it is exposed and use as an equipment grounding wire. You are not allowed to use a green wire for anything but equipment grounding but you are allowed to reidentify a different colored wire to become an equipment grounding wire.

    If this is a romex cable then you would have to change the wiring configuration in the panel and at that receptacle but it could be done as discribed above as I read 250.119.B.

    If this is an SE cable SE if I remember right can not be converted or used for any other use than service conductor or older dryer runs.

    What do you think?

    Just a thought


  6. #6
    Join Date
    Dec 2003


    WG, that's an interesting thought, but I thought that 250.119(B) couldn't be applied to dwellings.

    The preamble reads "where the conditions of maintenance and supervision ensure that only qualified personnel service the installation".

    I thought that limited it to commercial and industrial installations. Am I misinterpreting that preamble?


  7. Default

    I think I know what Romex cable is, but what is SE?

  8. #8


    SE can be identified by the fact that it has a "concentric neutral". This means that when you skin the jacket of the cable, the bare neutral strands will be spirally wrapped around the two insulated hot conductors. The concentric neutral is bundled and twisted to make a single conductor to put in the lug. Most older, 3 wire dryer setups were SE type cable, which is why Homer replied in the manner that he did.

  9. #9
    Join Date
    Dec 2003

    Default SE Cable

    SE= Service entrance cable: Type SE has a flame retardant, moisture-resistant covering. Service entrance cable can come as a single conductor or multiconductor assembly provided with or without an overall covering, primarily used for services (this includes USE=underground service entrance cable--yet USE does not require a flame retardant covering).
    Learning brings success. While you are waiting, I'm getting better!

  10. Default

    What I don't understand is the safety issue; if I have a hot, neutral, and ground all on the 3-prong RV recepticle, and the weathertite box is also grounded, what is unsafe?

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