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Here's the scoop:

There are 3 switches in my hallway. One switch on side A and two switches on side B. Side A switch controls same light as one switch on Side B. I replaced the switch on Side A and now, when the switches are in a certain configuration, you can hear a buzzing sound and then the circuit trips within 10-15 seconds.

I feel like its a grounding issue, but I don't want to touch anything till I'm sure. The switches all work as they should except for when a specific configuration of on/off exists, the circuit goes haywire.

Any ideas on what the problem is given that a buzzing sound happens and then the circuit trips?

There are two lights, switch A and switch B1 control one light, and switch B2 controls a separate light

The wiring/power source is unknown - could come from the 2 switches at opposite end of hall.

The switch had to be replaced due to physical damage of the switching mechanism

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Can you clarify a couple of things: (1) do all three switches (A, B1 and B2) control the same light? (2) Why did you replace switch A in the first place? (3) multi-way switches have a great many different possible configurations; can you describe the configuration of yours? For example, does power from the panel go to switch A, or one of the other switches? Does power to the light come from switch A or one of the other switches. And so on. – Eric Lippert Dec 2 '11 at 19:33
Also, obviously this situation is dangerous. The breaker is tripping before the house burns down due to overcurrent, but the breaker might not trip if your wiring fault happens to be dumping current to ground through a person or the wiring fault is causing a fire due to sparking. I would be keeping the circuit unpowered until you diagnose and fix the situation. – Eric Lippert Dec 2 '11 at 19:41
Call an electrician. – Tester101 Dec 2 '11 at 20:09
Did you replace switch on side A with a replacement 3-way switch? – The Evil Greebo Dec 2 '11 at 20:46

That sounds like a short to me, and a potential fire or electrocution hazard. Leave the breaker off while you fix this. With a 3-way light switch, you'll have two possible paths between the switches (which is why there are 3 screws + ground, 1 line/load, and 2 switched). My guess is that one of the two switched wires is grounding itself. Remove the switch that you worked on, and see if the ground wires are coming into contact with any other wires.

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First off, I agree with BMitch.

To diagnose the problem I would first want to understand the configuration of the two switches. The typical way these switches are wired is as follows.

  • Both switch boxes have two pieces of cable coming into them. One of the pieces of cable contains a white, red, black and bare wire. The other contains a white, black and bare wire.

  • In one of the switch boxes, the three-wire cable comes from the panel.

  • In the other one, the three-wire cable goes to the light.

  • The four-wire cable goes between the two switches.

So, first off, is that the situation you are in? That is not the only way to wire a three-way switch, but it is the most common. It looks like this: (Note that the bare ground wire is not shown.)

enter image description here

The way it works is: the first three way switch chooses whether the red or black wire to the other switch is connected to the black hot wire from the panel. One of the two is always connected.

The second switch chooses whether the red or black wire from the other switch is connected to the black hot wire to the light.

When both switches agree, the light is on. Otherwise it is off.

The first thing I would check is:

  • Are the white neutral wires connected to each other and nothing else? Never ever ever connect white to black.

  • Are the ground wires connected to each other and to the green safety screws on the switch? They should only be connected to things that should never be energized.

  • Are any of the ground wires bent in such a way that they are touching a screw that might be energized? Even slightly? That could explain your symptoms.

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The white wire is sometimes used as a hot wire if you have a switch that is at the furthest point in a configuration. Though it should have electrical tape on it that is anything other than green, or white (possibly yellow). This type of configuration is quite rare though. – Brad Gilbert Dec 3 '11 at 3:25

Either you mis-wired your switch, or there was some other problem which probably caused your old switch to fail.

If you replace a 3-way(US) switch, you need to make sure that you keep track of the common wire. It will be attached to a screw that is usually black, or copper colored. As long as your common is maintained you shouldn't have any problems.

Now to your specific problem.

I'm going to assume that when you replaced the switch you mixed up the wires, and have no way of remembering which wire is which. I'm also going to assume there isn't something else wrong that caused the original switch to fail.

If you are not comfortable around live wires, call an electrician.

Specialty Tools required:

  • non-contact voltage tester
    non-contact voltage tester

  • Simple neon voltage tester
    enter image description here


If at any point you are confused, or afraid of electrocution. Turn off the breaker, and call an electrician.

  1. Turn off breaker.
  2. Make sure it is off by using the non-contact voltage tester. ( After ensuring that the tester is in working order. )
  3. Remove all the wires from the switch.
  4. Make sure those wires are out of the way, and are nowhere near touching anything
  5. Make sure you leave a ground or neutral wire in a place where you can connect a probe, without fear of touching the other wires.
  6. Turn on breaker
  7. Attach one lead of the the neon tester to the ground or neutral wire.
  8. Determine which wire is currently live by using the other end of the tester, and keep track of it.

    ( Non-contact testers can give a false positive, so we don't use it here )

    If you have more than one live wire, call an electrician.

  9. Flip the other switch

  10. Determine which wire is currently live.
    If this is a different wire than the previous test, the two of them are your travelers. With the other one being the common wire. Otherwise it is your common wire with the other two being your travelers.

    Keep track of which one is your common wire.

    Again if there is more than one live wire, call an electrician.

  11. Connect one end of the neon tester to the live wire, and the other end to each of the other wires from the switch in turn. None of them should cause the neon light to light up brightly. Its okay if it lights up dimly, because the other end is probably just connected to the light bulb.

    If it does light up brightly call an electrician.

  12. Turn off the breaker

  13. Attach the common wire to the black or copper colored screw.
  14. Attach the traveler wires to the other screws.
  15. Attach a ground wire to the switch, unless it is going to be screwed into a grounded metal box. In which case it is probably optional, but may vary depending on your location. I usually connect it both to the box, and to the switch.
  16. Make the switch safe to flip.

    You can do this in several ways

    • Tape the back of the switch twice around, with electrical tape. Make sure that it will stay on when you flip the switch.
    • Screw it back into the box. It doesn't have to be screwed in all of the way at this point. ( recommended method )
  17. Turn on the breaker.

  18. Test the switches.

    If you just taped the switch. Grab it in one hand by placing your thumb on the end of one tab, and placing your index, and middle finger on the other end. Make sure that all of your fingers are touching each-other, and nowhere near anything other than the tab. Use your other hand to flip the switch.

  19. If it works, install the switch after turning off the breaker. If it doesn't work, call an electrician.

  20. Install the cover plate.
  21. Turn on the breaker, if it isn't on already.


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