WiremanWireman · 3-way switches don’t work right: troubleshooting for electricians · 2023 NEC ·
3-way switches don’t work right
Light only works from one switch, or in some positions. Find the common and fix the travelers.
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How it works
A 3-way switch has three screws: one common (usually a dark or black screw) and two travelers (usually brass or light). Inside, the common connects to one traveler or the other depending on the toggle. The line hot lands on the common of one switch, the common of the other switch feeds the light, and the two traveler wires run between them. Flipping either switch moves the path from one traveler to the other, so the light toggles from both places. Almost every 3-way problem is the common landed on a traveler screw.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- What does the light do?
- Works only when the other switch is in one positionWas one of the switches just replaced or rewired?
- Yes, one was just replacedTest: Identify the common wire with a meterExpect: At the switch where power comes in: one wire reads 120 V in both positions. At the switch by the light: two wires take turns reading 120 V and the third never does.
- One wire is hot in both positionsThe common is on a traveler screw
- Two take turns, one never hotThe common is on a traveler screw
- Nothing reads 120 V in any positionThe other switch is miswired too, or the feed is lost
- No, it stopped working on its ownTest: Test each switch for continuityExpect: Common beeps to one traveler in one position and to the other traveler in the other position. The two travelers never beep to each other.
- A switch fails one of the checksA worn-out 3-way switch
- Both switches test goodAn open traveler or a loose connection
- Yes, one was just replacedTest: Identify the common wire with a meterExpect: At the switch where power comes in: one wire reads 120 V in both positions. At the switch by the light: two wires take turns reading 120 V and the third never does.
- Never comes on from either switchTest: Follow the power through both switchesExpect: One switch has 120 V on its common all the time. At the other switch, one traveler or the other has 120 V, depending on the first switch.
- No 120 V anywhereNo power reaching the switches
- Common hot at one switch, travelers dead at the otherAn open traveler or a loose connection
- Travelers hot at the second switch, light still deadThe problem is between the second switch and the light
- The breaker trips when a switch is flippedA neutral or second hot landed on the switches
- Works, but quits or flickers now and thenA loose connection or worn switch
- Works only when the other switch is in one positionWas one of the switches just replaced or rewired?