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Thread: Power to a double switch

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  1. #1

    Default Power to a double switch

    I had a bathroom ceiling fan on a switch.

    i replaced the fan and hooked it up to a new switch -- with two off and on's on one post

    please forgive my electrical ignorance.

    i want to run a separate light fixture off the second switch... so i ran the wire from the switch to the light... the light has no power.

    do each of these switches need to have their own power source?

    i guess i am thinking the circuit to the fan would supply power to the light as well.

  2. #2
    Jack of all trades frenchie's Avatar
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    I can think of so many different ways this might be configured... where is the power coming in from - the switch box, or the fan box? A diagram would help...

  3. #3
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    In general, the power source (e.g., black wire from the panel) goes to the common side of the dual switch, and the other two (switched) sides go to the appliances' hot sides. The appliances share the neutral. As Frenchie points out, the topology is slightly different if the power comes from the panel to the switchbox or the fan's box, but a few minutes spent with a pencil and the back of an old envelope will be well spent to get the picture of what's going on.

  4. #4

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    boy, I am sure both of you guys would be a tremendous help.

    I just have to figure out some of the terminology.

    Some of this is difficult because the fan wiring is in the attic... since it worked fine, i just hooked it up to the top switch

    then i put a can light in the ceiling and ran wiring from it down to the lower switch, black to brass colored screw, white to black colored screw, ground to green colored screw.


    my guess is either that white wire or the black wire from the can light has to be tied to the fan switch

    you can laugh a little... i am patient.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    I can't follow your wiring, but by hooking the white to the switch, it in effect became a black, red, or blue wire, not a white one. You still need to find a source for a white neutral wire to the fixture. And that is assuming the "black" wire is actually connected to a "hot" wire.

  6. #6
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Since you "just hooked it up to the switch", I assume there were only two wires going from the fan box to the switch box -- probably a black/white pair. Another black/white pair should have brought power from the panel to the fan box. The black wire from the panel (the "hot" wire) should have carried current via the black wire to the switch, where it was switched on and off to the white wire (which should have been marked with black paint or tape). Back in the fan box, the white wire from the panel (the "neutral") should have been connected to one of the fan wires, and the white wire from the switch box (which also should have been marked with black paint or tape) should have been connected to the other fan wire. The complete circuit is then hot from the panel, through the switch, through the fan, and return to the panel via the neutral.

    Now we introduce the double switch. If you look at the switch terminals, one side of the switch will have two black screws in 2 brass strips connected by a small tab, the other side will have two brass screws in two separate brass strips, each obviously associated with one of the individual switches. The black wire from the fan box should be connected to one of the black screws, and the white wire (which should have been marked with black paint or tape) should be connected to one of the screws on the other side of the switch. Notice that the black ("hot") wire from the fan box is now actually feeding both switches, via the little tab connecting the two halves of the brass strip -- the 2nd switch is all dressed up with no place to go, i.e., nothing's connected to it.

    Now to connect the light, you've somehow got to get a wire from the other separate screw on the switch to one side of the light, and the other side of the light to the white neutral wire from the panel in the fan box. How you do this is up to you, but in new construction I'd run a three-wire cable from the fan box to the switchbox (one "hot", 2 switched) and another 2-wire cable from the fan box to the light box (one switched, one neutral).

    Draw some pictures and it might make sense. Of course if any of my initial assumptions is wrong, none of this works. If that's the case, do what Frenchie suggested and draw us a picture, or describe what's going on in all 3 boxes (fan, switch, and light) in detail.

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