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250V plug wiring question

Discussion in 'Electronic Basics' started by Jay, Jun 4, 2007.

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  1. Jay

    Jay Guest

    I have a line cord with black, white and green conductors. I wish to
    use it to connect to a 250V plug. Except for the green ground, does it
    matter which of the other two are connected to which terminal? The
    screws do not have the bronze and chrome colored screws. Both are
    bronze colored.
  2. Doug Miller

    Doug Miller Guest

    That's because it doesn't matter which wire goes where -- 240V circuits use
    two hots and a ground, but no neutral. The two hots are interchangeable.

    Note that my response assumes you're in the US or Canada. If you're not, then
    you need to specify where you are, because the answer may be different.
  3. Jay

    Jay Guest

    Thank you. I'm in USA
  4. DJ Delorie

    DJ Delorie Guest

    In the USA, both "hots" are equivalent. The transformers that feed
    your house are 240V center-tapped, with the CT connected to your
    neutral and the other two taps being your two hots. The neutral is
    bonded to earth ground at one point in your wiring, usually at the
    main circuit breaker panel.

    However, to prevent confusion, you should take a red marker and mark
    the ends of the white conductor, so that other people looking at your
    wiring don't think you thought it was 120v wiring.

    With 3+1 wiring, the hots use the black and red wires, neutral uses
    white, and bare/green is for ground. If you only have black and
    white, it's a good idea (sometimes it's code) to color the white wire
    red to indicate its actual purpose.
  5. Doug Miller

    Doug Miller Guest

    For cord-and-plug connections -- which I think is what the OP was talking
    about when he said he had a "line cord" that he wanted to connect to a 240V
    plug -- this is unnecessary. The differing plug configurations mean that there
    is no possibility of a 240V plug *ever* being used in a 120V receptacle, or
    vice versa.
  6. DJ Delorie

    DJ Delorie Guest

    I was thinking about the other end - which would be inside the wiring
    box of the device. If it's a universal motor, which can be wired for
    120 or 240, it's best to know what the original wirer intended.

    And if you do one end, you should do the other end.

    My paranoia is based on seeing a 120v outlet (not mine) wired to
    black/white/ground wire, with the other end wired to a 240v ganged
    circuit breaker. Pvsst.
  7. Doug Miller

    Doug Miller Guest

    That can be inferred from the plug on the end of the cord.
    Proper color-coding of the wires would not make that any less dangerous.
  8. Don Bowey

    Don Bowey Guest

    If the white wire is to be used as a hot lead, US code requires that it be
    taped with black tape to alert workers that it it hot. Certainly that makes
    it less dangerous.

  9. Doug Miller

    Doug Miller Guest

    Excuse me? The situation under discussion is an already-existing 120V
    receptacle that is already incorrectly wired to the two hot leads of a 240V

    Please explain how proper color-coding of the wires to this inherently
    hazardous receptacle makes it any less hazardous.
  10. DJ Delorie

    DJ Delorie Guest

    No, it doesn't. Re-read the original post.

    The OP has a black/white/green wire, and wishes to use it to connect
    [I assume a 240v device] to a 240v plug. Nowhere was a 120v outlet
  11. Rich Grise

    Rich Grise Guest

    Don't do it. Get a proper 250V plug and socket.

  12. Doug Miller

    Doug Miller Guest

    Yes, it does. I wrote that in response to your description of an existing
    outlet. Re-read the thread including the context you snipped.
    Yes, there was -- by you, in the post to which I wrote that response.
  13. Doug Miller

    Doug Miller Guest

    Huh? He already *has* a 250V plug. The cord he's asking about connecting to it
    is perfectly fine for that purpose.
  14. DJ Delorie

    DJ Delorie Guest

    Ok, that does. But I try not to go off on tangents, so forgive me for
    not losing track of the original intent of this thread.

    The mis-wired outlet incident only fueled my paranoia, it wasn't
    intended to be an example specific to this thread. If it's going to
    confuse the issue, I hereby retract it, and you may safely ignore my
    anectodes thereof.

  15. Use red 'phase tape' on the white wire at both ends.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  16. Jamie

    Jamie Guest

    Assuming single phase systems?, it does not matter as long the
    line cord can handle the voltage and load. seeing that this is a
    plug you're referring to, it's assumed you are plugging it to a
    proper 250 volt receptacle and the device it's connected to requires
    250 volts?
    remember, the plug is what is in your hands that you insert, the
    receptacle is what's on the wall with the female insertion prongs.

    If you're trying to branch off a couple of new circuits to get 120
    from a 240 outlet, don't do that. the proper way is to use a sub box
    with de-rated breakers from that circuit and not from the receptacle,
    also this kind of system is not allowed where the possible use of
    life saving equipment maybe depending on the circuit because if for
    some reason the main breakers for the 240 tripped out, it would also
    trip out the 120 volt sub.
    The code for that is very questionable to say the least.

    I have a heavy line from the main panel going over to the work bench
    that is #6-4 (red,black, white and ground), this gives me a 240 source
    and i have a sub panel/breakers that gives me the 120 I need. The main
    breakers for this line are 50 amps, the subs are 15 each.
    I also have all of this in EMT pipe because it's low enough to be
    reached by hands and code states it has to be covered some how. I guess
    they don't think romix jacket is sufficient any more other than used
    inside an enclosure of some kind.
  17. Rich Grise

    Rich Grise Guest

    Oh, sorry. Then use the red tape as others have suggested (or red paint,
    magic marker, etc), assuming green is earth ground.

  18. Don Bowey

    Don Bowey Guest

    Someone posted this in response to that.

    I posted the following:

    You posted:

    No, you aren't excused, but thanks for asking.

    Seeing two black conductors, or one red and one black still says both are
    hot. If one is white a person might unknowingly think it is a neutral.
    That is what the code prevents.

    Got it now?
  19. Doug Miller

    Doug Miller Guest

    Code doesn't prevent people from doing stupid things with electricity, as
    should be obvious from DJ Delorie's description of a 120V receptacle that was
    wired onto the two hot legs of a 240V circuit. I was responding to your
    contention that this situation would somehow be made less hazardous by the use
    of proper color-coding on the wires. Code obviously did not prevent some fool
    from having wired the receptacle that way; there is no particular reason to
    suppose that proper color-coding would have done any better. Given that the
    outlet ALREADY EXISTS in that condition, it is not made any more, or less,
    hazardous by altering the colors of the wires that feed it.

    Got it now?
  20. Circa Mon, 04 Jun 2007 18:31:53 GMT recorded as
    Certainly it would. It would inform anyone with a proper understanding of
    electrical wiring that the wires she or he was working with were not meant
    to be used with a 120VAC receptacle. In the situation as described, the
    receptacle was properly wired, according to the color code of the wires at
    the receptacle end.
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