Can 3-way wiring that works be wrong/dangerous?

Question

I recently replaced a single pole switch with a 3-way. After following diagrams on many sites and watching several instructional videos on how 3-ways work (learning terms like "traveler" and "load", etc), I finally got it working. My only concern is that there is a scenario where the switches work as intended, but the wiring is not correct and an electrical fire is in my future.

Attached is an screenshot of a diagram I followed, from a video that matched my setup.

Thanks for your knowledge.

Update - Not sure if this is important, but on my switches (Leviton) the side with the single connection (excluding the ground) is at the bottom, opposite to the black on the other side.

Sorry that I don't know the correct terms.

The "On"/"Off" will **not** work as shown. Or rather, it will 1/2 the time. It actually works out to "On = Both **same**/Off = Different" or "On = Different/Off = Same" depending on how you wire it up. — manassehkatz-Moving 2 Codidact, Sep 05 '21 at 20:34
On your shematic you missing some wire. No voltage supply for new switch. If it works, it is miracle. — user263983, Sep 05 '21 at 20:59
@manassehkatz-Moving2Codidact Everyone who's ever used a "3-way lightswitch" knows they work that way... — user253751, Sep 06 '21 at 08:17
@harper-reinstatemonica Mystery and science things are not compatible. Science based on repeatable things. If you are joking, use " ". — user263983, Sep 06 '21 at 11:43

score 9 · Answer 1 · answered Sep 05 '21 at 21:29

This is safe as long as the black, red-black, and white-black wires between the switch boxes are all in a single conduit or cable. That is, the switched-hot and the two travelers must be physically adjacent outside a junction box.

Same is true for the neutral and hot from the panel to the old switch box, and for the neutral and switched-hot between the old switch box and the light fixture.

In the diagram: That kind of switch does not actually have "ON" and "OFF" positions. You have not drawn the wire nuts inside the old switch box. Otherwise it looks very good. You have even indicated the neutral going to the shell connection on the light fixture.

The whole thing looks not only safe, but best practice. Congratulations on getting it right.

Can 3-way wiring that works be wrong/dangerous?

1 Answers1