3 way light switch wiring question
 

Howdy all,

I'm hoping there is someone that might be able to point me in the right direction.

My kitchen lighting uses two 3-way switches that do not appear to be working properly. The lights only work when both switches are in the down position. Any other combination and they are off.

I have looked at a few articles and YouTube vids on it, but apparently I'm just not getting the picture.

Currently they are both wired the same way. Looking at the switch from the user's perspective:

Upper left = red wire
Upper right = white wire
Lower right = black wire, labelled COM

Any ideas?

Thanks!

Brian

In a 3-way switch you have 1 ground terminal and 3 "hot" terminals:

- The feed wire goes to the common terminal of one switch.

- The other two terminals turn on/off opposite from each other; meaning, when the toggle is in one position, one of the terminals is off and the other is on. When you flip the switch the other way, the off terminal is on and the other is off.

- At the other end, the two "hot" wires go into the two other switch terminals.

- The common terminal is hooked to the load.

Basically, it's just a SPDT switch. An easy way to tell if you have the right kind of switch is that a 3-way switch (SPDT) or a 4-way switch (DPST) will not have "on" or "off" markings. There is no "on" or "off" marking on the toggle because either position can be on depending on the switch position on the other end. BTW: 4-way switches are used in between two 3-way switches...

An alternate wiring method could have the power feed could be coming into the load side and the switches switch the neutral side. But the same arrangement applies.

As far as wiring goes. On either end, you'll have black (hot), white (neutral), and green/bare (ground) wires. In between the two switches, you typically have an extra red wire.

Here is a link that explains the wiring: http://www.homeimprovementweb.com/in...way-switch.htm

Here is a more basic schematic which might be clearer:

http://2.bp.blogspot.com/-UD_LlFf4Su...ng-diagram.jpg

The kitchen in my house had a 3-way setup and was totally messed up. One of the positions on one of the switches actually blew a breaker. The best way to figure out what is what is to remove the switches , open the light fixture, and identify the wires (be careful if doing this while power is hot).

You could simply have worn switches too. Over time, the arc that happens when you open/close the switches can eat away at the metal making no connection. Even if the switches "may" be good, I would replace them with new ones that way you are starting with known good components.

Great electric lesson.
 

WOW BG thanks for that drawing. I have worked on a few three way switches in my time and never quite understood how they worked until I took a close look at that drawing. When I did that big remodel in California last June we had a three way setup that was not working correctly. So I just played around with the switches hot until I got them to work right. I still don't know what the heck I did, but it works great now. These switches have always been a kind of mystery to me. Thank you for clearing that one up for us.

NP. Actually, I got that drawing from a google image search using the terms "3-way switch schematic".

A schematic always makes things clearer (at least to me). Wiring diagrams are pretty clear too, but can be a little more confusing since they usually don't show the actual electrical paths in the components themselves. And the real-world wiring at a junction box can be a nightmare to sort out.

Yea I hear ya there BG. No really this helps out a lot. When I did that big remodel job on our house in Cali last June one of the more complicated jobs for me was pulling the original 1950's power panel out and replacing it with a new updated home panel. I took a whole bunch of photos before I started and taped them to the wall so if I got confused at all I could go back the way it was previously. Once you get started it is really not that hard to figure out what wires are coming from where. And of course I could set up the breakers any way that I wanted to as long as I balanced out the "A" & "B" legs evenly.

Once I was done though we had a scare because I knew I had everything right, but no lights and it was already about 8 or 9 pm. SO I hit up the neighbor for a little sparky help and it only took a few minutes for him to figure out that the main on the back of the house was going bad. One leg was fried because they had a piggyback wire tied directly into that leg to power a makeshift A/C unit that was hanging in the wall between the garage and the dining room when the wife bought the place. So I ran on over to the Home Depot and found the main ($165.) for one breaker. I was not very happy about that, but at least I know everything in that electrical system was replaced with brand new breakers. I removed that piggybacked wire and everything was golden from there. I finally got the lights on around 1030pm using flashlights to work in the dark.

The funniest thing was when I opened up the wall to remove the old panel and found all of the ground wires twisted together OK, but just hanging inside the wall. It was never grounded during construction in 1956. SO then I had to get one of those ten foot grounding rods and drive it into the ground to make the connection legal and up to code. It took me over two hours to drive that dammed thing 9.5 feet into the ground with a claw hammer. Live and learn, right?

I have always wondered myself how those switches work, that drawing makes it clear as day

Thanks for the detailed info!

Question: I purchased two new switches. COM is marked for the black "hot" wire. The other two posts are unmarked. How do I know which wire goes where on the remaining two?

It doesn't matter as long as the "travelers" (black and probably red) are hooked to them - just don't hook a neutral (white) or ground (bare/green) to them.

Awesome. It's all fixed now. Turns out the new switch was bad too. I measured continuity at the switch posts and determined that it wasn't making the connection properly in the "up" position. I replaced it with another switch and it's working like a champ now.

Thanks again!