Lv 4
Justin asked in Science & MathematicsEngineering · 1 decade ago

How does a light controlled by two different switches work?

In my house, there is a dining room with two different light switches that control the same light. I always thought that a light switch works by opening and closing the circuit controlling the flow of electricity to the light.

However, if the light can be turned on and off by both switches then how does the circuit really work? For example, if I walk into the room with both switches set on off and the light is off and turn one of the switches on, turning the light on then walk over to the other switch turning it to on as well. Instead of giving the light more power, it turns the light off. This puzzles me because it shouldn't be opening the circuit that the other switch is physically closed on.

10 Answers

  • 1 decade ago
    Best Answer

    The two switches are both "single pole double throw" type, in which the thrown pole switches back and forth between two conductors.

    You run two parallel conductors between the two switches (call them the "upper" and "lower" wires). Each switch flips back and forth between upper and lower on the thrown pole, and the two non-thrown poles attach to the power source.

    So if both switches are on the upper wire, current flows; and if both switches are on the lower wire, current flows; but if one switch is on the upper and one is on the lower, no current flows.

  • M.
    Lv 7
    4 years ago

    A single pole switch, has 2 contacts, 2 wires and is either ON or OFF. A 3-way switch (2 are used in the system) has 3 contacts, three wires and is Position 1 and Position 2 (no distinct on-off positions). A 4-way switch has 4 contacts, 4 wires and is Position 1 and Position 2 (1 or more 4-way switches are used between two 3-way switches, for 3 or more locations of control). This is simple when you understand it, and unintelligible when you don't understand it.

    Source(s): Electrical guy since the 1960s
  • Anonymous
    1 decade ago

    It is possible to turn on a light with two switches. both possitive and negitive wires are connected to the two switches. I have three switches in my basement that control a set of lights. each swich controls the same lights. If you use one switch to turn on a light, the other will turn it off, and vise versa.

  • 1 decade ago

    You ares still opening and closing one circuit. The two switches are made to be used together, (called a three-way switch), by supplying two routes for the electricity to take to get to the light.

    Power comes to the fist switch, then has two wires going to the second switch, then one wire to the light. (Not counting the neutral)

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  • Jack
    Lv 5
    1 decade ago

    Those are called two-way switches, or two-pole switches. When you move the switch, it opens one pole, but closes the other. The power for the light routes through both poles of the switch. If both switches are closed on the same pole, the light goes on.

  • looks like U have standard three-way switching for that light.

    easiest way to check...

    single pole switch is marked on/off (also has only 2 screws)

    three-way switch is unmarked or blank (also has 3 screws)

    hot leg it connect to one side of one switch, two wires (called travelers) run between each switch, and the switch leg is run from the second switch to the light.

    Source(s): check this out.... http://home.howstuffworks.com/three-way2.htm
  • 1 decade ago

    mxzptlk & Keith P & Jack & macssvt....t... all have competent answers to your question.

    I will try to make you a wiring diagram to make this a little clearer. notice the section of 3 wire between the switches

    N wwwwwwwwwwwwwwwwwwwwwwwwwwwww Ln

    ...........................S rrrrrrrrrrrrrrrrrrrr S

    P bbbbbbbbbbS ........................... S bbbbbbbbbbbbb Lp

    ...........................S bbbbbbbbbbbb S

    N neutral

    P power 110V

    S switch

    Ln neutral to load (light)

    Lp power to load (light)

    w white wire

    b black wire

    r red wire

  • 3 years ago

    Indestructible Tactical LED Flashlight - http://FlashLight.uzaev.com/?qhHm

  • 1 decade ago

    Simple circular circuit being capable of being interuped or completed by the flip of either switch in the circut.

    Source(s): I wired them on three separate occasions... really quite simple. Check out any electical "how-to" book.
  • 1 decade ago

    not quite sure...but that's a pretty interesting question

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