23 posts / 0 new
Last post
m_albertsen
Adding 3-way switch

I currently have 2 lights (one can light and one fixture) hooked to 1 switch. I would like to add a switch on the other side of the room. I understand I would need to replace the existing switch with a 3-way and install a new 3-way where I want the new switch. I looked at the existing switch, and there is not power coming in there, so the power must be coming in at one of the lights (I haven't been in the attic space yet to see which light the power is coming in). Could anyone please help me with a wiring diagram to install these 3 way switches? Thanks.

JLMCDANIEL
Re: Adding 3-way switch

There are about 300 different combinations for wiring 3 way switches. We need to know what you have in place now to provide your drawing.

Jack

Edgeking
Re: Adding 3-way switch
HoustonRemodeler
Re: Adding 3-way switch

Your drawing will looks something like this;

Power supply
(feed) ---- Switch ---- Fixture ---- Switch

OR

Switch ---- Fixture/feed ----- switch

OR

Fixture ----- switch ---- switch --- feed

OR

Fixture ---- switch ---- feed---- switch

OR

Something like that

We need to know what wires are where, and what kind they are. To run 3 way switches, you'll need a 3rd wire at your switch (usually red) to make the other switch work.

Fencepost
Re: Adding 3-way switch

The easiest way to do this, from a "making the connections" standpoint is to NOT open up the boxes at the light fixtures, but to connect the second switch only to the first switch.

To do this, you'll need to run 12/3 cable (if it's a 20 Amp circuit) or 14/3 cable (if it's a 15 Amp circuit) from the original switch location to the location where you want the new switch. If you're not sure, install 12/3 cable. It can be used safely on 20 Amp or 15 Amp circuits, but 14/3 may not be used on a 20 Amp circuit. You'll also need to purchase two "3-way" switches.

The 12/3 or 14/3 cable will have three insulated wires: black, red, and white. The 3-way switches will have three terminal screws; one of them will be black and the other two will be brass.

TURN OFF POWER AT THE CIRCUIT BREAKER OR FUSE BOX BEFORE PROCEEDING.

Note: we don't need to know which of the wires at the existing switch is "hot." The procedure listed below will work whether it is the white one or the black one.

AT SWITCH A:

  1. Remove the existing switch (we'll call this location "switch A") and discard it or put it in your collection of spare parts. This will leave a black and a white wire hanging out of that electrical box, going to the lights. Mark the white wire with black tape or black marker, if it isn't already -- code requires this.
  2. Install one end of the triple-cable into this box with about 6-8" of the individual wires exposed. Mark the white wire on this cable the same way you did on the existing cable.
  3. Cut a short length (6 to 8 inches) of bare wire of the same gauge and connect it to the green grounding screw on the new 3-way switch. With a wire nut, connect this to the two bare wires in the existing cable and the new triple-cable.
  4. Connect the two BLACK wires together with a wire nut. Make sure there is no bare wire showing outside of the nut. These wires will NOT connect to switch A.
  5. Connect the MARKED WHITE wire from the existing 2-wire cable to the BLACK screw of switch A.
  6. Connect the remaining MARKED WHITE and RED wires in the triple-cable to the remaining two brass screws of switch A. It doesn't matter which wire goes to which brass screw.
  7. Double-check your connections. Make sure the bare ground wires do not come in contact with any other screws on the switch.
  8. Install the switch into the box and install the cover.

AT SWITCH B:

  1. At the new switch location (we'll call this "switch B"), install an appropriate electrical box and install the other end of the triple-cable with about 6 to 8" of the individual wires exposed. Mark the white wire in the same manner as at switch A.
  2. Connect the bare ground wire to the green ground screw of switch B.
  3. Connect the marked BLACK wire to the BLACK screw of switch B.
  4. Connect the remaining MRKED WHITE and RED wires in the triple-cable to the remaining two brass screws of switch B. It doesn't matter which wire goes to which brass screw.
  5. Double-check your connections. Make sure the bare ground wires do not come in contact with any other screws on the switch.
  6. Install the switch into the box and install the cover.

Turn the power back on, and test.

A couple of notes on technique: type NM cable ("Romex") is required to be fastened to the surface over which it runs every four feet. If run in an accessible basement or attic, it should run alongside or through holes bored in joists; if run across and below or on top of the joists you need to install a stringer board next to it to protect the wire. When making connections at the switches, the wire should wrap clockwise around the screw so that it doesn't sneak out from under the screw head when you tighten it down.

TECHNICAL NOTE: Above instructions edited to reflect that the white wire, though marked, must be used as a traveler between the switches.

JLMCDANIEL
Re: Adding 3-way switch

Fencepost,
While your scenario will work it does not meet current code.

Jack

Fencepost
Re: Adding 3-way switch
JLMCDANIEL wrote:

Fencepost,
While your scenario will work it does not meet current code.

Jack

Please elaborate.

My description is essentially the same as the fifth diagram on this page: http://www.wfu.edu/~matthews/courses/p230/switches/3way/variations.html

or diagram "B" on this page: http://www.thecircuitdetective.com/3and4wyinfo.htm#threevary

EDIT: I found some information that some people interpret the NEC such that the marked white wire between the switches must be used as one of the travelers. I've updated my previous post to reflect this.

Fencepost
Re: Adding 3-way switch

UPDATE: apparently, the 2011 National Electrical Code requires a neutral at all switch locations, to provide for certain types of electronic switches. (Certain exceptions apply, where accessibility to the switch location allows a neutral to be easily added later.)

Since this is an existing installation without a neutral (installed prior to the code change) you can probably convince your electrical inspector that it is infeasible to rewire the switch(es) to provide a neutral. Or you could run 12/4 between the three way switches, and NOT USE the white wire, but use the blue wire instead of a marked white wire in my description above.

Whew. This is getting confusing.

Here is an excellent video that explains the code requirement.

JLMCDANIEL
Re: Adding 3-way switch

Fencepost,
As the first switch has no neutral at it's location and is a device change , it would require replacing the 2 cond cable with a 3 cond cable to get neutral to the first switch location and 4 cond to the new switch location. I don't believe an inspector worth his salt would accept a device change as being grandfathered with old code requirements and definitely would not accept the new switch and wiring without the neutral unless both switches are direct drops from an unfinsihed attic .

Jack

JLMCDANIEL
Re: Adding 3-way switch

The new code 404.2(C) is going to cause a lot of confusion, especially when dealing with inspectors that are poorly trained or don't read well.

Jack

canuk
Re: Adding 3-way switch

Here's another thought that should meet code requirement. However it does require opening the light j-box that has the branch supply feed.

It appears the branch supply feed is in the light j-box -- which likely means there are black and white conductors at the existing switch box ( lets call it A ).

Since the gauge of wire -- 12awg or 14awg is unknown -- lets call it X

Run X/2 drop from the existing light j-box to the new 3 way switch ( lets call it B )
From switch B a run of X/2 to switch A

The white of the existing X/2 from switch A gets moved and connected to the neutrals at the light j-box --- the other end of this white is capped with a wire nut if not used at the switch box.

The black of the existing X/2 from switch A is connected to the switched feed to the lights. ( at the light j-box ). The other end of this black at the switch box is connected to the *common* screw of the new 3 way switch.

The black and white from the *new* X/2 drop between switches A&B are connected to the *traveller* screws at both switch A&B.

The black of the X/2 from the light j-box is connected to the constant supply feed at the light j-box . The other end of this black will connect to the *common* screw of switch B.

The white will have the end at the light j-box connected to the neutral bundle with the other end capped with a wire nut in the switch B box if not used.

This way you are suppying the required neutral to the switch locations ---- using more commonly available and cost effective cabling ---- and depending on switch box sizing likely not be concerend with over stuffing.

The exception will at the light j-box ( branch junction ) which likely requires a change to a larger one or an additional j-box to accomodate the extra connections.

Pages

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.