Cfxtrjtrk

Apologies if this question is answered elsewhere. I couldn't find it specifically.

I'm planning on installing two multi-gang switch boxes, where all of the switched lighting will be on the same branch circuit. Both of the boxes will have a 3 way switch, which in combination will control one set of lights. All other switches in these boxes are single pole switches.

I'm trying to determine the best way to provide power to each of the switch boxes. Considering I need to run travelers between the two boxes, is it permissible to run a 4 conductor cable (2 travelers, 1 hot, and 1 neutral, 1 ground) between the boxes? This allows me to bring power into one box and through to the next box for additional switched wiring.

Thanks, once again, for your help in advance!

Yes, that's fine. From the box with the supply coming in, You can run a /4 cable between the boxes --

• always-hot (e.g. Black)


• neutral (must be white) - this works because all loads are on the same circuit


• two travelers (red/blue, or red/white-red depending on if it's 12/4 or 12/2/2 cable).

However in this configuration, the onward power to the lamp must come from the other box.

If you want supply and lamp coming into the same box, you would need /5, and at that point, for availability reasons, you are better off using /3 and /2. The /3 would be entirely dedicated to the spur 3-way, and its white wire would not be neutral. Onward hot and neutral would be in the /2 cable.

As always, you are better off using colored tape to mark the wires by their purpose instead of being stuck with the default colors of cable, which are to distinguish wires. The two travelers don't even need to be distinguished, I mark both with yellow tape.

In the /4 or /2/2 configuration, you cannot substitute two /2 cables for the /4. You will get eddy currents and vibration between the cables if you do: fatigued wires, arcing, trouble. The wires in a cable are bound tight together for a reason.

The cable between the two 3-way switches is already normally a /3 cable - 2 switched-hot travelers (i.e., only one carrying power) and the neutral (not connected to the switches but connects to the switched light and must parallel the travelers).

If you want to add another set of loads, you would actually need /5 - 2 travelers, 2 neutrals (one for 3-way lights, one for the other load), hot for the other load. Which really means just use a /2 and a /3 run together or run 5 separate wires in a conduit (colored/marked appropriately).

Thanks to Harper for more details:
This can be done with a /4 using a single neutral, provided the lights are connected to the 2nd of the 3-way switches:

panel/power --> switch 1 --> travelers/hot/neutral --> switch 2 --> lights and other load

This way the neutral current matches the combined hot (other load) and travelers (3-way lights). However, this could be a little confusing for anyone working on this in the future. Plus, if you ever wanted to split the loads to different circuits you would not be able to do so - though with LED lighting that is far less of an issue than it used to be.