3-way switch feeds another switch?

Discussion in 'Electrical Forum discussion & Blog' started by yar02169, Aug 22, 2011.

  1. yar02169

    yar02169 New Member

    Messages:
    35
    Location:
    Quincy, MA
    I want to add a motion sensor to a pair of lights on the outside of a garage. Upon investigating today, I got confused by what I found.
    SW1 is in the house, SW2 is in the garage, and has never been used, so I can remove it for the sensor. Here's what I found that gets me. SW2 is next to another switch (SW3) that operates the lights inside of the garage. When tracing the wires, line in (from the switch in the house, SW1) comes to SW2 on one side of the switch, a Red wire is connected to the other side, runs up to the next box, which contains connections for the outside pair of lights, and wiring for the inside light connections. It connects to the Black pair for the outside lights.
    That makes sense, but how the heck is the inside light powered? Everything functions correctly, but I'm not sure what will happen when the motion sensor is installed. I don't care about the 3-way function after the sensor is installed, but I don't know how the inside lights are powered.

    Breakdown:
    Line-In from SW1(inside house) to SW2 (left posts), Red goes from opposite side of SW2 (right post) up to Box1. In Box1, Red connects to L1 & L2 Black.
    SW3 Black goes to Box1, connects to Red(in) that goes to inside light (L3in)
    SW3 White goes to Box1, connects to Black(in) that goes to inside light (L3in)
    White from L1, L2, L3(in) are all connected together.

    SW3 operates independently, but I don't understand how. If SW2 Red feeds to L1 & L2, how does SW3 get fed?

    The sensor should be an easy thing to install. I assume it would be a replacement of SW1 to a regular switch, and wire as normal, ignoring the extra 3-way wires.

    Thanks in advance for any advice.
    Ray
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,532
    Location:
    North Carolina
    What kind of motion sensor are you installing that goes where the switch is located? I always installed motion sensors for outside lights on the light itself.

    What you describe in your breakdown I can't see as working for any of the lights.
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,515
    Location:
    Cave Creek, Arizona
    Trying to make sense of S1,S2,S3, L1, L2,L3,right, left, etc. has me completely confused, BUT nowhere in that Kludge do I see ANYTHING about two traveler wires, which indicates that there are NO 3 way switches in the system. From your description, I can not even be sure if any switches are in series. When I have more time, I may try to draw a schematic from your posting and see if I can decipher it.
  4. yar02169

    yar02169 New Member

    Messages:
    35
    Location:
    Quincy, MA
    Describing electrical circuits is a tough one, as I'm sure you all know.

    The motion sensor is a replacement sensor, which is usually mounted in the same box as the lights. In this case I plan on mounting the sensor at the peak of the garage for best range, and the lights are on the sides of the garage door. Instead of 2 lights and a sensor in one box, the 'box' will be the front of the garage.

    Trying to clarify the circuit;
    SW1 operates the outside garage lights from inside the house.
    SW2 does the same thing, except it's located in the garage. SW2 was never known to exist, so it can go away during this project.
    SW3 is located next to SW2 inside the garage, and it operates the inside garage light (L3).
    L1 & L2 are the lights outside the garage, which I would like to be operated by SW1 and the motion sensor.
    SW3 operates L3, which is inside the garage.
    My guess is the actual Line-In goes to SW1, as it is in the house and not out in the garage, that would be a savings of material and time to do it that way, and I'll double check it.

    While doing research, I found a diagram for a 3-way switch and a hot receptical. I'm thinking that is basically what I need, where as the receptical would be the inside garage circuit (SW3 and L3), but from what I can tell, it's not how the circuit is currently wired. http://www.electrical-online.com/how-do-i-wire-a-3-way-switch-to-control-a-light-plus-keep-a-duplex-receptacle-hot/

    I'm heading back to try to figure this out some more, but I'm not to confident.
    Fingers crossed.
  5. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,532
    Location:
    North Carolina
    Install three wire cable from the light to the point where the motion sensor is to be mounted.

    Disconnect the black and white wires from the light and connect them to the black and white in the new cable using a short piece of white under the wire nut with the two white wires to connect back to the light. Connect the red wire to the light.

    At the sensor connect black to black white to white and the red wire in the cable to the third wire on the sensor.

    Close up the switches as you have no need to do anything in the box or boxes that contain the switches.
    Install three wire cable from the light to the point where the motion sensor is to be mounted.

    Disconnect the black and white wires from the light and connect them to the black and white in the new cable using a short piece of white under the wire nut with the two white wires to connect back to the light. Connect the red wire to the light.

    At the sensor connect black to black white to white and the red wire in the cable to the third wire on the sensor.

    Close up the switches as you have no need to do anything in the box or boxes that contain the switches.
  6. yar02169

    yar02169 New Member

    Messages:
    35
    Location:
    Quincy, MA
    Wow, that was a very simple solution. I thank you fo
    r help. It's nice not having to understand how it was wired, but still be able to get it working.
    Thanks Again,
    Ray
  7. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,532
    Location:
    North Carolina
    You are very welcome
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