3 Way Switch Wiring Diagrams (page 1) (page 2)
In the above diagram we have the 2 wire cable going to the light from the other 3 way
switch. In this case the feed wire is connected directly to the common on the switch in
the box on the left. The neutral or white wire gets spliced to the white in the 3 wire
cable that goes to the other box with the 3-way switch and then that gets spliced to the
white going up to the light. That carries the neutral to the light. The black wire from the
light is connected to the common on the 3-way switch on the right. Again I want to
emphasize that the wire colors I am giving are the standard in the electrical industry.
You could very well encounter different color wires.
On the topic of connections, the mechanics are extremely important when
it comes to electrical connections. Splices should be twisted tight with no
spaces, but not so tight the wire breaks. Screws should be secure and
tight as well. I frown upon using those push in connections on the back of
switches and receptacles. The contact they make is poor and tends to
In the above diagram we have the feed entering at the light box. In this case the neutral
gets connected directly to the light. The black or hot wire is spliced to the white going to
the 3-way switch box. Once at this box the wire is spliced to the white going to the next
3-way switch box and connected to the common. The black going to the light is
connected to the common on this 3-way.
Now let’s look at a fairly common scenario.
In the above diagram we see the feed enters the light box. In this case we have a 3-wire cable
from the light to each 3-way switch. The red and black traveler wires get spliced through in the
box at the light, black to black and red to red, being sure they are the wires from the two 3-wire
cables. The white or neutral from the feed is connected directly to the light. The black or hot wire
is connected to the white on one of the 3-wire cables and is connected to the common on the
3-way. The white in the other 3-wire cable is connected from the common on the switch to the
Repeating what I said earlier, when using a white wire as a hot leg, it should be marked with a
piece of black tape to signify it is, or could be hot.
The next diagram is something you may see but it is not the correct way of doing
this. It is a shortcut I have seen in older installations. I only include so that if you
see it you'll know what's going on.
In the above diagram we see something a little unusual. I have included this because I have
seen variations of this done, especially in older installations. Notice that no 3-wire cable is used
and there is a feed in two locations. Are you are wondering why would anyone do this? Well
there were a couple of reasons. One is they did not have to use any 3-wire cable. When a
contractor was doing a whole slew of houses the savings were enough that I guess it was
worthwhile. One really bad aspect of this method is many times the feed in one box and the feed
in the other are from 2 different circuits. This causes an imbalance in the main panel. You may
also see in this scenario that there are wires exiting these boxes being fed from these feed
The above wiring diagram shows how to add an additional light. On any of these installations
there can be multiple lights connected to the same set of 3-ways. They would just be paralleled
with the one light.
That should cover most of the different scenarios. As I said earlier there are many combinations
so you may run into something unusual. If that’s the case, feel free to email me with the details
and I will try and help you figure it out. Before making the assumption that there is a problem
with the wiring don’t overlook the obvious. One is making sure the switches are all working
properly. It is not at all uncommon for a switch to go bad.
To check a 3-way switch it should first be removed from the wiring. You will need a continuity
tester preferably with a light or beep sound. It is important that the switch is not connected to any
power or you could be seriously injured. One lead of the tester goes on the black or common
screw. The other lead goes on either of the brass screws. If you get a light or tone switch the
switch and the light or tone on the tester should go out. Now move the lead from one brass
screw to the other. You should now get a tone or light on your tester. Basically you should get
continuity from the common to one brass screw with the switch in one position and the other
brass screw with the switch in the other position. The way the switch works is illustrated below.
|(C)Copyright 2005 Forte Electric Inc.
3 Way Switch Wiring Diagram