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Wiring A Switch: One NM Run Or Two Best ?

Discussion in 'Electrical Engineering' started by Robert11, Mar 30, 2005.

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  1. Robert11

    Robert11 Guest

    Hello:

    Over the years, I have done a bit of relatively simple wiring around the
    house.

    Have just finished reading the book by H. Richter, Wiring Simplified, 40th
    ed.
    with great interest. A very handy little volume.

    Have the following question for those of you who might be doing
    this stuff for a living, please:

    Whenever I have wired a new wall switch, I have always brought a piece of NM
    wire from
    the source to the switch, the black going to one terminal.
    Then I ran a second piece of NM with the black from the other switch
    terminal to the new light fixture,
    along with its white lead. (the whites would also be tied together for the
    two pieces of NM at the switch box).

    I see in the book (p 110) where it is apparently permissible to just use a
    single piece of NM to the switch, with the white being re-marked black.
    This NM would then effectively be placed in series with the normal black
    wire from the source and to the fixture. (the white from the source also
    going to the light fixture).

    The approach i have been using which I described in the first paragraph
    isn't even described in the book.

    So, other than the first approach using twice the amount of NM, is there any
    advantage one way or the other ?

    What do you folks do in a simple situation like this ? Why ?

    Thanks,
    Bob
     
  2. Brian

    Brian Guest

    Look in your book under 1960's wiring methods. Renaming sucks.



    Hello:

    Over the years, I have done a bit of relatively simple wiring around the
    house.

    Have just finished reading the book by H. Richter, Wiring Simplified, 40th
    ed.
    with great interest. A very handy little volume.

    Have the following question for those of you who might be doing
    this stuff for a living, please:

    Whenever I have wired a new wall switch, I have always brought a piece of NM
    wire from
    the source to the switch, the black going to one terminal.
    Then I ran a second piece of NM with the black from the other switch
    terminal to the new light fixture,
    along with its white lead. (the whites would also be tied together for the
    two pieces of NM at the switch box).

    I see in the book (p 110) where it is apparently permissible to just use a
    single piece of NM to the switch, with the white being re-marked black.
    This NM would then effectively be placed in series with the normal black
    wire from the source and to the fixture. (the white from the source also
    going to the light fixture).

    The approach i have been using which I described in the first paragraph
    isn't even described in the book.

    So, other than the first approach using twice the amount of NM, is there any
    advantage one way or the other ?

    What do you folks do in a simple situation like this ? Why ?

    Thanks,
    Bob
     
  3. Guest

    If you want power to be available at the switch
    box location (for example, for a combination
    switch/receptacle) you have no choice - you must
    run a cable from the source to the switch location
    and a cable from there to the light.

    If the above is not the case, then the physical
    layout determines the best way.

    An additional advantage (besides possibly using
    less wire) to a switch loop versus 2 cables is box
    fill. When you add a second cable, box fill
    calculation increases by 4 cu in for #14 wire, or
    4.5 cu in for #12 wire. A small utility box is
    not code compliant for a switch and 2 cables.

    Ed
     
  4. Good point about the box fill. Also about needing power in the switch
    box. I've retrofitted my house with X10 switches, receptacles, etc. X10
    switches (switches that can be controlled either manually or remotely
    via X10 commands) require a hot and neutral to the X10 switch and
    provide a switched hot out to the controlled fixture. I've been caught a
    few times when the existing switch had only one NM run, i.e. no neutral.
    My solution was to pull in a 12-3 plus ground. One NM cable with two
    hots, a neutral and a ground. The second hot (red) was used for the
    switched leg.

    If I were wiring my next house and I didn't mind spending a few bucks,
    I'd think about running 12-3 to each switch.
     
  5. Roy Q.T.

    Roy Q.T. Guest

    Wiring A Switch: One NM Run Or Two Best ?

    Group: alt.engineering.electrical Date: Wed, Mar 30, 2005, 12:56pm
    (EDT-1) From: (Robert11)
    Hello:
    Over the years, I have done a bit of relatively simple wiring around the
    house.
    Have just finished reading the book by H. Richter, Wiring Simplified,
    40th ed.
    with great interest. A very handy little volume.
    Have the following question for those of you who might be doing this
    stuff for a living, please:
    Whenever I have wired a new wall switch, I have always brought a piece
    of NM wire from
    the source to the switch, the black going to one terminal. Then I ran a
    second piece of NM with the black from the other switch terminal to the
    new light fixture,
    along with its white lead. (the whites would also be tied together for
    the two pieces of NM at the switch box).
    I see in the book (p 110) where it is apparently permissible to just use
    a single piece of NM to the switch, with the white being re-marked
    black. This NM would then effectively be placed in series with the
    normal black wire from the source and to the fixture. (the white from
    the source also going to the light fixture).
    The approach i have been using which I described in the first paragraph
    isn't even described in the book.
    So, other than the first approach using twice the amount of NM, is there
    any advantage one way or the other ?
    What do you folks do in a simple situation like this ? Why ?
    Thanks,
    Bob
    ~~~~~~~~~~~~~~>
    I've come across your wiring method before, it leaves 2 uneccesary white
    conductors spliced in a box. it was a color code issue, and it's been a
    while since the NEC Geniuses along with Manufacturers, Electricians &
    Homeowner$ decided it was a foolish demand at that level.

    I'd Just run a 2 conductor cable to the switch box it seems nobody even
    bothers covering the white wire black, as they say, if a guy doesn't
    know what wires run through a switch he shouldn't be in there to begin
    wih };-)

    when you work with rigid conduit (emt) you'd run a red & a black only to
    the switch., it's nice nec manners to follow color codes when & if you
    practically can.

    ®oy
     
  6. Jimmie

    Jimmie Guest

    I mark white wires used as hot with a piece of heat shrink tubing. Never
    heard of anyone running two pieces of NM for this purpose.
     
  7. Guest

    It is done frequently, and is the most economical way
    in many cases. Here's an example:
    source==NM#1==Switch===NM#2==Light

    Say from a receptacle box (source) to a switch directly above
    it to a ceiling light. Two NM cables enter the switch box, the
    whites are spliced and the blacks connect to the switch.

    Ed
     
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