# Why would both switches on a 3-way switch fail simultaneously?

My kitchen has six canister lights controlled by a pair of 3-way switches. Yesterday, I flipped one of the switches on and nothing happened. I tried the other with the same result.

When I check the voltage, I get 92V on one switch for both pairs of wires regardless of the switch position. On the other I get 92V from one pair regardless of the switch position, but only millivolts from the other pair if in one position, 92V if in the other position. The lights do nothing regardless of either switch's position.

Do I need to replace one switch? Both? Call an electrician?

• The 92V is phantom voltage and is meaningless. It only tells you that those wires are near a wire that is hot. Jun 20, 2017 at 1:25
• How are you measuring the voltage (from what to what)? Jun 20, 2017 at 10:44

Thank you for the comments. All were accurate and educational - although after picking up a new switch and installing it with no luck, my wife asked how I had ruled out the other switch. As I was about to try the other switch, she said "no, I mean the third switch by the back door". I didn't realize there was a switch by the back door other than the porch light. Sure enough that switch was halfway between on and off. As soon as it was flipped on, all of the lights worked again - although I felt pretty foolish.

• The saying in troubleshooting is "When you hear hooves, thinking horses not zebras". In other words, first check the simplest things before you get to the more complicated things. Occam's Razor is another good rule of thumb. Glad you found the problem. Jun 21, 2017 at 8:23
• @CoBill in this case you have a 4 way system and not a 3 way. For your situation - you probably were fortunate and replaced a 3-way switch with a 3 way and did not get to the 4-way. The third switch in your arrangement is a 4 way. See here: do-it-yourself-help.com/4_way_switch_diagram.html
– Ken
Aug 28, 2017 at 2:25

I wouldn't pay too much attention to the 92V unless there is some true current (amperage) running through it as it might be trace voltage.

This diagram belongs to do-it-yourself-help.com. The original can be found here: https://www.do-it-yourself-help.com/3_way_switch_wiring.html

You need to find the source voltage and confirm you have power there. In the image above it is sourcing from one of the three way switches and it will always terminate there. That's where I would start looking, try and find the source voltage of 120V and start working from there. The other common is always the switch leg. Then you have the two carriers.

I know this sounds stupid but did you check the breaker and made sure you had power to the switches? Most of the time failure is at the weakest points. That would be splices and connections and the switches themselves. So go through and check all splices, connections and switches one at a time. Switches do break so look for actions that feel broken or are making noises like something is loose or broke free. Normally switches do not go bad together but even one going bad could stop the lights from working. The good news is that it is rare for the problem would be in the light fixtures, but that doesn't rule them out. It would just be the last place I would look.

This failure could be a problem due to the following

1. The wiring down wind from the switches to the lights may have open circuited.
2. You may have wiring that was done with quick connect poke in installation. These are prone to failure more often than one cares to think.
3. Maybe there was an electrical surge that happened to take out all of the lights at once. Narrow possibility but could happen.

Any time the lights are on, current is flowing through both switches -- after all, that's the reason why not only can either switch turn the lights on, but either switch can also turn the lights off, by interrupting the current flow.

A physical failure inside either switch where the failure mode is such that it breaks the internal electrical contacts could prevent the other switch -- which is perfectly fine -- from switching the lights on.

Assuming only one switch has failed (the problem could be somewhere else, not in either switch), the most intuitive guess is that the switch having no impact on the measured (phantom) voltage when flipping the toggle from one position to the other is the one that has failed.