Older Three Way Circular Dimmer Switch-All wires go to one terminal?

[vyacheslav]

Greetings,

Please take a look at the photos below. What is currently wired is an older three way circular dimmer switch (with a push on/off). I am going to be replacing it with a modern 3 way dimmer with an off/on toggle switch at the bottom (Levitron) and am completely confused which wires are supposed to go where. Usually, I take a picture with my phone and just repeat the pattern on the new switch, but the new switch has three separate terminals (entry points) for the three wires. Black to black- black to red and beige to red!! As you can see, it is the older wiring (non-Romex) with out a grounding wire inside the box. The house was built in 1950 so I assume that's original wiring in the box.

Can anyone make me a road map or provide guidance?

Thanks!

V

 

[afjes_2016]

If there are no markings on the back of the original switch in the way of "red" indicating what it is I would have to go with: Look at the back of the original switch to make sure there is nothing to indicate what each wire is or especially the "common". "Common" is the most important one to know.

In this case I would have to think that the present switch "red" wire is connected to what should go to your "common" screw on the new switch and the other two black wires are your travelers which don't matter which of the other two screws on the new 3 way they go to.
On the new 3 way switch you will have 3 screws (forget about the ground screw if it has one at this point). Of the 3 screws two will be the same color (usually silver) and one will be darker. If the screws are all the same color then look at the back of the switch. One of the screws should have imprinted "common". You would take the wire nut off of the wire that is connected to the red wire on the present switch and connect that wire from the box to the new switch marked "common" or the darker screw. Then take the remaining two wires and connect them to the other two screws on the new switch; again it won't matter as these are travelers.

Before you do this take some tape and wrap a small piece around the wire in the box that the red wire from the present switch is connected to so you don't mix them up.

Of course make sure the proper breaker is off. Turn the light on and flip the breaker (not the switches) that controls this light. If the light goes off then you have the proper breaker. Leave it off while you move the wires from the old switch to the new switch.

Someone else please double check me on this but logic would tell me I am correct.

 

[PJB12]

I made a quick sketch for you that may help you visualize the voltage paths in a 3-way switch.

Assuming the electrician wired as-standard:
The house wire that is connected to the red wire from the switch in your first photo is either from the circuit breaker or is to the lamp. This depends on if the switch is the first (left in drawing) or second (right in drawing) switch.

The two other wires are called "Travelers". They go from switch to switch. As Afjes mentioned, you can interchange them on the new switch. If it was wired as-standard, I would connect the red to the terminal on the new switch that is a different color than the other two (usually a dark screw) and the travelers to the other terminals (usually silver color) and try it.

It may help to open the box where this NM cable originates. It might be the lamp box, or the other switch box. Studying the wiring in this box will certainly help you figure out who is who in your shown box.

You can also label all wires, unhook the next switch and unscrew the lamp(s), Then, use a tone tracer like those used by telephone service people to find out which wire is which. The only other way is by using a voltage meter, an ohm meter and jumpers. This should be left to an electrician because the voltage meter work is done live.

About the beige wire:
In the older NM cable, the white often changes color over time due to the tar in the outer jacket of the cable. This is the beige one in your drawing. It's meant to be a neutral, but in a switch set up, it's re-assigned to carry line voltage.
It should have been coded a color (not white, grey or green) with a felt pen or tape.

One important note is that many new dimmers have a terminal for a neutral. This is for dimming LED bulbs. I don't know if your new dimmer has it, or if it will work without connecting it when incandescent bulbs are used.

I hope this helps you sort things out.
Paul

 

[vyacheslav]

Holy Moly! I just checked back in on this thread. Thank you SO MUCH for all the effort and time in making that diagram, Paul. You Rock! This is very helpful!