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bkasl 01-02-2009 03:43 PM

Adding a 2 way switch to a 3 way circuit
I have an overhead kitchen light controlled by two 3 way switches, we want to add an undercabinet 2 way light off the wall of one of the 3 way switches so it can be controlled independently. I have the 14/3 wire loose with the new 2 way switch in place along with undercabinet lights, how do I tap into one of the 3 way switches so the undercabinet light can be controlled seperate from the overhead lights? Thanks Brent

Speedy Petey 01-02-2009 04:25 PM

First off there is no such thing as a 2-way switch. What you are describing is a single pole switch.

The only way you can do this is to tap of the 3-way that has the feed. You cannot
do what you propose by tapping off the 3-way that has the switch leg coming off of it.

bkasl 01-02-2009 04:28 PM

Do I need to replace the 3 way with a 4 way then tap into the single pole? Is their a wiring diagram I can reference? Seems all the wires are their, or I can make some piggybacks if need be, thanks

joed 01-02-2009 05:16 PM

There are at least eight different ways to wire three way switches. Depending on which way yours is wired will determine how you add the new switch or if you can even add the switch.

If the box with the existing three way has only three wires in the box then you can NOT add the new switch without pulling new cables.

some three way wiring diagrams

AllanJ 01-02-2009 07:30 PM

You need to find where the power source (unswitched power) and neutral come in to feed the existing subcircuit of three way switches and the lights they control.

You cannot feed your new switch and lights from a point in the middle of that subcircuit.

Using a voltmeter you would want to find a hot wire that is always live (120 volts to neutral) regardless of the positions of the 3 way switches.

YOu do not want to add a 4 way switch; that diagram is not the diagram you want.

220/221 01-03-2009 01:49 AM

You need a voltage tester.

Pull out the 3 way switch in the box you want to tap into.

Test between the common terminal (dark colored screw) and the bare ground wire (or the box if its metal). If you have power there, flip the switch. If you still have power, you have the right box.

If you lose the power on the common terminal by flipping the switch, you need to get power from the other box or another source.

bkasl 01-03-2009 08:29 AM

Single pole switch in the middle of the box has two black wires that are both hot when on.
Their is a red wire to the 3 way behind the box cutout for the new single pole that seems to be always hot when the overhead light is either on or off. Is it possible to piggytail into this one for power to the single pole, then join all 6 whites together including new single?

AllanJ 01-03-2009 09:40 AM

(General rule) Do not combine whites that were not combined to begin with. Do combine all grounds (bare and green) wherever they come together.

(More specifically) Some whites go to switches in the same or another box and are hot (not neutral). They should be marked with red or black tape or stain at both ends but are sometimes not. If you have different hot feeds entering the box, say, going to the existing 3 way and the existing single pole switch, the accompanying neutrals (from the respective cables) should not be tied to each other.

Once you find a hot wire that itself is not controlled by any switches (probably the red wire you mentioned) you may use it and its accompanying neutral for your new light and switch. Note the arrangement of wires and cables at the back of the box.

If a white wire is connected to a switch, you may not use the accompanying black or red wire as a hot feed for something else. (That white is hot and the appropriate neutral does not come to the box.)

220/221 01-03-2009 01:45 PM


Single pole switch in the middle of the box has two black wires that are both hot when on.

If you have a sp sw in the box, you have power and neutral.

One of the blacks goes to a wire nut connection, that is your hot. The white wire in that cable is the neutral and it will also go to a wirenut.

For your new switch you need anothe hot pigtail for power, The black wire in your new cables goes to tyhe other sw terminal. White in the new cable goes to neutral.

Pictures are much easier, it saves a lot of guessing, questions and assumption.

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