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Thread: Power to a double switch

  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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    Default

    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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    Default light

    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.

  7. #7
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Okay, I just studied your description a bit. I think you can make all this work by disconnecting your existing light-to-switch white wire at both ends. Then connect another white wire (the white wire in a two-wire cable works OK) from the light to the white wire from the panel in the fan box. Logically, we're moving the end of the light-to-switch white wire from the switch to the system neutral.

  8. #8
    Moderator & Master Plumber hj's Avatar
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    Default wire

    That description is not much better than the original one. He is probably already using the "white wire in the romex" for the switched lead to the fixture, and what does he do with it once he disconnects both ends? But he probably does need another white wire for the neutral, we just don't know how he is going to run it.

  9. #9
    Retired Defense Industry Engineer jadnashua's Avatar
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    WIthout being there and measuring things, it is hard to say, but this is my guess.

    At the fan, there's two cables coming into it; one from the power panel, the other going to the switch. The white wire coming from the power panel is connected directly to the fan. The black wire from the panel is jumpered to the other wire that is going to the switch. It goes down to the switch, and when the switch is closed, it comes back to the fan on the white, which is connected to the black wire to the fan, providing it with power. BTW, this wire is supposed to be labled with a red marker to indicate that it is a switched hot lead, but is ignored way too often.

    So, you need to verify this, and you need to continue the white wire from the power panel to the white wire of the new light. Then, with the new lead from those lights to the new switch, at the switch for the fan, connect both black leads together with a couple of pigtails, and then go to each of the switches, providing power to both items when their respective switches are closed. Leave the white wires where they are, but mark them with red tape or a red magic marker.

    The grounds need to run all the way through each item, but I left that out.

    If you don't own one, you need either at the minimum a test lamp, or a meter.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  10. #10
    Jack of all trades frenchie's Avatar
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    Quote Originally Posted by Mikey
    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).
    You were doing so well - but that "one hot 2 switched" is wrong - it'd be one hot, one switched, and one neutral. Like HJ said, what Lee's probably missing is a neutral for the light circuit. Assuming that by wiring in the attic, he means the power enters there...

    By the way, ALL of you are wrong about the white wire marked as hot. If you re-designate a white, it can't be the switch leg returning to the light, it has to be the constant "always hot" wire.

    http://forums.jlconline.com/forums/s...t=38064&page=2

    (I always hesitate to link to JLC... it's a pro-only site, and we/they can be mean about it. If you're not in the trades, feel free to lurk, but do not post unless you like getting flamed.)

    The idea is that, at the fixture's connections, you're always going black-to-black, white-to-white, no matter what, it saves on confusion for the next guy.


    Lee - describe each box, will ya please? How many wires in each box, and where do they go?

    Do you have access to the attic? Or are the walls open? It'd help to know where it's easier for you to add a wire, because you're gonna have to do it somewhere.
    Last edited by frenchie; 08-05-2007 at 03:05 AM.

  11. #11

    Default

    I will print and follow these posts..

    here's the best i can tell... power came from the basement panel..up the wall to the ceiling to a junction box... then it split... to the fan... and then back down the wall to the original switch.. there, a pair of wires was attached to the switch..

    everything worked well.

    then i took out the single switch and attached the fan to the top switch.. fan works great..

    then i put the can in the ceiling and ran romex from it down to the other switch.

    Please allow some patience for my ignorance.. I will take a Sunday break... and thank everone for their help...

    i'll let you know next week, where I am ..... even with A/C ,,,it seems to hot to work today...

    regards,

    Lee
    Greenville, SC

  12. #12
    Moderator & Master Plumber hj's Avatar
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    Default light

    Those two wires down to the switch are both "hot" when the fan is on. You do not have a white neutral to the light, so it cannot work. If the black wire is the switched leg, then the white one is "hot" which can be more confusing, and dangerous to a DIY person. I would rather have him confused by the wiring than in the emergency room because he touched a "safe" white wire. And if it happened to me, I would be looking for the idiot that wired it that way.

  13. #13

    Default

    Just to let everyone know some more info..... the ceiling is more or less buttoned up now.

    the wall is still open. And, there is romex coming up from the basement into a wall plug box (the plug is in the adjoining bathroom) A wire comes out of that same box and feeds another light switch.

    I presume that's a possible solution to complete the circuit. I need to take a breather.

    They should teach this stuff in high school rather than another history class. I tried to decipher it in books, but forget it.

    HJ--- i'll play it on the safe side, I keep running up and down the stairs from the basement, turning the breaker off an on...

    Actually most of the wiring looks decent.. it's a 1930's bungalow...but all of the knob and tube has been replaced...

  14. #14
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Default I stand corrected... partly

    I said "one hot, two switched", and that is in fact the situation, although I would have been wrong about the colors. Having read through the Code (God, I wish they had had an English major on the team that wrote the damned thing) and the JLC thread, I now see that my "one hot" would be the reidentified white conductor (coming from the black in the light outlet and going to the common switch terminal), and the "two switched" would be the black and red conductors (coming off the switched terminals and returning to the fan and light) in a "standard" 14-3 cable.

    Someday I'll figure out how to draw pictures for this forum and save a hell of a lot of words.

  15. #15
    Jack of all trades frenchie's Avatar
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    If he runs a 3-wire, there's no need redesignate the white, anyways - it'll be one hot, one switched, one neutral. I think you missed what I was saying.

    Anyhow...


    Drawings? Google Sketchup!

    Give me a few minutes... here we go!


    Lee - replace the 2-wire cable between the fan & the switch with a 3-wire cable. This is how it should look when you're done.
    Attached Images Attached Images  
    Last edited by frenchie; 08-05-2007 at 04:04 PM.

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