I'm a bonehead - three way switch help

Discussion in 'Electrical Forum discussion & Blog' started by vic3, May 4, 2009.

  1. vic3

    vic3 New Member

    Messages:
    5
    Hi all - I was rushing through replacing a light fixture this weekend, and disconnected the wiring without noticing what I had. Turns out there was more going on than I realized. The fixture (light #2 in the attached) is controlled by two switches, and is down the hall from another light (light #1 in the attached) controlled by two other switches. After disconnecting the wiring for light #2, light #1 no longer works. There are three sets of wires (B, W, bare copper ground in each) in the can for light #2, and I found one wire (a black wire) that seems to be hot regardless of how the switches are positioned. I can't find the proper hook up to get everything working again. Any ideas or recommendations would be appreciated. Next time I'm taking a photo before I touch anything.

    Regards

    Attached Files:

  2. Thatguy

    Thatguy Homeowner

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    Two way switches act like one single pole single throw switch and this arrangement is in series with the AC source and the controlled lamp.

    Assuming the controlled lamp is a 100w incandescent, if you substitute a 100w incand. for the two-switch-arrangement, both lamps will be on at 1/4th power. Then, the two wires that go to the substituted lamp are what needs to go to the two way arrangement. The trick is to find which of the two wires are correct, but at least with the bulb there won't be sparks and tripped breakers.

    There are many ways to wire this arrangement.
    http://en.wikipedia.org/wiki/Switch
    Last edited: May 4, 2009
  3. vic3

    vic3 New Member

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    Thanks Thatguy - I should have mentioned that I'm a novice too - Some of you terminology is unfamiliar to me. I'm not sure how to proceed based on your reply.
  4. Thatguy

    Thatguy Homeowner

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    Another way is go with the wire colors and for this I'd look in one of those DIY books for house wiring.

    For electricians the colors tell all. They are as good as a schematic, assuming the colors are correct.

    I don't recommend doing this by trial and error; there are too many combinations.

    If your house is one of many wired identically perhaps you can copy a neighbor's wire colors and wiring arrangement.

    Do you have a multimeter?
  5. vic3

    vic3 New Member

    Messages:
    5
    Ah, ok - I had found some schematics online, but none seemed to fit what I've got. I thought I had a "three way switch with power source at the fixture" but that still left me with an extra set of wires. I'll try one of the books. Also, I do have a multimeter which is how I found that the one wire is always hot - can I use it in some other way to narrow things further?
  6. Thatguy

    Thatguy Homeowner

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    If two wires are the same color they might be the travelers.
    If you find a wire that's hot, load it down with any incandescent bulb between the wire and a known good ground and see if the voltage stays at 120v; otherwise you might be reading a phantom voltage.
    http://en.wikipedia.org/wiki/Phantom_voltage
    After you turn off the breaker, and check that there is no voltage, if your meter reads down to 10 or 20 ohms between two wires that is probably the cold filament resistance of the [good] incand. bulb that is being controlled.
    If your ohmmeter reads zero between a known good ground terminal and a wire, that wire is a neutral or ground wire.
    If your ohmmeter reads infinity between a known good ground terminal and a wire, that wire is a traveler or a hot wire that is off because the breaker is off.

    If you post photos and diagrams and keep track of all wires with labels it is possible that this can be figured out. A helper comes in handy as does an extension cord to verify continuity between distant wire ends.

    It's a tedious process of elimination but I'm up for it.
    Last edited: May 4, 2009
  7. vic3

    vic3 New Member

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    dumb question - exactly what do you mean by loading it down with an incandescent bulb - am I simply touching the wire to the base of the bulb?
  8. Thatguy

    Thatguy Homeowner

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    When you measure voltage, put an incand. lamp across the voltmeter leads so that the lamp is being powered while the voltmeter is being powered.
    This
    http://images.lowes.com/product/converted/032664/032664481000md.jpg
    might come in handy.

    They have "lo-Z" voltmeters to prevent reading phantom voltages. Wiggys are also immune to phantom voltages.

    Each wire you check can go:
    -nowhere (a traveler)

    -to 120v
    -to neutral/ground

    -to neutral/ground through a lamp filament
    -to 120v through a lamp filament

    http://tonyelectric.com/short-orders/2-short-orders/7-what-is-the-meaning-of-the-wire-colors
    Last edited: May 4, 2009
  9. Alectrician

    Alectrician DIY Senior Member

    Messages:
    689
    Need more info on the wiring.

    Include the wiring in the switches as well.
  10. Thatguy

    Thatguy Homeowner

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    A three way switch is a single pole double throw [SPDT] switch.
    It has a wiper [hopefully with a colored screw] and two stationary terminals.

    There should never be continuity between the two stationary contacts, and as the switch is flipped the continuity changes from the wiper to one stationary contact and then from the wiper to the other contact.

    With the wire colors and the one hot lead that you found we have already narrowed down the choices.
  11. vic3

    vic3 New Member

    Messages:
    5
    Thanks for trying to help me guys - I'm realizing that figuring this out may be beyond my ability and time available - gonna call an electrician in the morning.
  12. hj

    hj Moderator & Master Plumber Staff Member

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    Location:
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    switch

    The hot wire and its neutral would normally be the start of the circuit. But, after you tie the hot to the common of a three way switch, you should have a neutral white going to the fixture along with TWO wires to the next three, or four, way switch. With just a black and white, you either do not have the necessary third wire, or the neutral is being handled differently. Your system may require someone in house to decipher the circuitry.
  13. Thatguy

    Thatguy Homeowner

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    Hope you get one who is
    honest
    competent
    having a good day
    whose heart is in his work.

    The good news is this should be a trivial task for any electrician.
  14. Alectrician

    Alectrician DIY Senior Member

    Messages:
    689
    Don't feel bad. We get calls like that all the time.

    Last week, a homeowner replaced all their switches/receps. They called, saying that their AC wouldn't work.

    We got there and every single breaker, except one, was OFF.

    What the???

    Turned everthing on, tested and found that they 1) didn't break the tabs on the !/2 switched receps and 2) got all the 3ways wrong.
  15. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,472
    Location:
    Cave Creek, Arizona
    customer

    At least it sounds like they were consistent. Good thing none of the split receptacles were being fed by two legs of a 240 v feed.
  16. Thatguy

    Thatguy Homeowner

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    Why don't they check as they go??
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