Extending power from existing three-way switch circuit

Question

I have 2 circuits of 4 lights connected via two 14/3 cables to two sets of switches that on/off each circuit. Power comes in at Switch1/circuit 1. All works fine.

I want to extend power from second set of switches to new single pole switch just two feet from that second set. The new single pole switch will control one dining room light. How do i extend power to next switch so that it works independent of the other switches?

Answer 1

Let's go to the store and get some colored tape, so we don't lose our minds. We don't need to distinguish two travelers from each other, so a pair of travelers can be the same color. We do however have two sets of travelers in close proximity, and two switched-hot colors which I'm making red and purple.

So now in color:

In order to feed an additional switch+lamp combo, you need always-hot and neutral. Do you see it in the right hand switch box? Yes, you do, but how?

Well, you've got always-hot in one cable and neutral in the other cable -- Oh wait.

You can't do that

You can't pull power off one cable and return it on another cable. Currents must be equal in each cable. The answer is "NO".

It would be yes if they were all wires in one conduit. Using cable between the switch groups sinks you.

Answer 2

I am highly curious as to why you couldn't put a couple of diodes on the traveler wires and splice them together to provide your single 120v line to the side switch you are adding? That way regardless of which way the switches were flipped the diodes ensured the hot legs going into the 2nd outlet 3 way would be hot.

Id assume something about the equal return voltage could be why not, just curious as it seems that'd be simple to accomplish. For me, all my switches are Leviton DMZX15 switches I think, which are Z Wave Smart Switches for all sorts of loads so you need to always have power to them. In a triple gang box I was trying to have the load side of the 3 way provide the line power to the other two load switches. Diodes seem like a potential solution for pulling solid power off of the travelers on the 3 way outlet switch.

Not an electrician, just a DIYer and always interested student!

Answer 3

You DO have what you need at the second set of switches. Use the White wire with the black tape on it to feed your single pole switch. The other cable has the neutral wire in it, so you can use this as the return with the new lighting load you'll add.

Preliminary: Turn the circuit off and lock the cabinet door, get a battery light to work with.

1. Run a 2-wire(Black,White) cable between the new light box and the second set of switches.
2. Remove the White wire marked with black tape from the common screw of the left 3-way switch and splice it together with two short lengths ("pigtails") of black wire with the same gauge.
3. Reconnect one pigtail to the 3-way common screw.
4. Connect the second pigtail to one screw on the new single pole switch.
5. Connect the black wire of the cable you ran in step 1 to the other screw of the single pole switch.
6. Splice the white wire of the cable from step 1 in with the other two white wires that are already wire-nutted together.