Why is my three-way switch not working?

donzoh1 · Jan 7, 2023

One of my switched ceiling lights or the wall switches (three-way switches at separate entrances to the room) is not working properly. The light will work with some switch positions. With switch A in one position, switch B works properly. When switch A is in the other position, switch B will not work. Also, I have measured a significantly low voltage (maybe 30v) at the fixture with certain switch positions. The house is 20 years old and I'm not sure whether this problem developed over time or if it was present at construction. Is this more likely an issue inside of a switch or improper wiring?

Vortigern · Jan 7, 2023

Well we know the light is ok as it does switch on and off. So it is the switches. One of the wires has probably come out at one of the switches. If not that then it was always wired wrong. You should have a two way switch at each end and an intermediate switch in the middel. Sometimes called a cross-over switch.

James · Jan 7, 2023

It is also possible that prior to you moving in, the switches were changed to freshen up the look.
an intermediate switch may have been changed to a 2way switch? Or the wires have been put in the wrong terminals at one of the 2 way switches.

brianmoooore · Jan 7, 2023

What's all this with the intermediate switches? The OP is in Yank land, so 3W = 2W. (no idea where they get the third way from.)
Answer will probably be as above. Wire come adrift or someone's been playing and reconnected the originals or new wrongly.
The 30V will probably be a 'phantom' voltage, caused by capacitance between parallel wires, and will disappear when any load is connected (although can cuse LED lamps to glow).