3-way switches are used to allow two light switches in different locations to control the same light fixture. This adds safety and convenience to homes. For example a long hallway might have switches on each end to turn off or on the hall light, or a stairway often will have switches both at the top and bottom of the stairs to control a single light. 3-way switches are fantastic when they work as intended, however it’s very frustrating when they don’t! Troubleshooting is needed to fix 3-way switches that are not functioning properly.
Troubleshooting 3-way switches can be a bit of a daunting task, especially if you’re not an experienced electrician. However, with a bit of basic wiring knowledge and some careful attention to detail, it’s actually a relatively straightforward process.
Today we’ll cover one of the common issues that can arise with 3-way switches, as well as some tips, techniques and examples for troubleshooting them.
Fixing Improper Wiring on a 3-Way Switch
One of the more common issues that can arise with a 3-way switch is that the switch itself is improperly wired. Meaning all of the necessary wiring is present and accounted for, but the person installing the 3-way switch mixed up some wires, now one switch location works fine but the other switch location only works when the first switch is in the right position.
First you’ll want to start by turning off the circuit breaker in the electrical panel that feeds the 3-way switches you’re having trouble with. Make absolutely sure the power is off on each 3-way switch with a non-contact voltage tester.
Next take off the cover plate and look in the box to see what kind of insulation is on the wiring.
If it’s housed in a metal box and the wiring looks to be knob and tube, put the cover plate back on and call a certified electrician: the wiring should be replaced! If you live in the Seattle area, call OHM Electrical Contracting at (206) 678-6744 or use our online form.
At each switch you should have three insulated wires and one non-insulated grounding wire. If it looks like newer wire, nm-b or Romex, remove both 3-way switches and carefully wirenut each wire that is attached to both switches, ensuring no bare copper is exposed past the bottom of the wire nut.
At the first switch location you’ll have one wire that feeds power from the breaker panel to the first 3-way switch. At the second switch location you’ll have one wire that goes from the second 3-way switch up to the light fixture. The two other wires attached to the switches are what are commonly known as travelers. Two wires going from the first switch location to the second switch location.
How to Correctly Identify Each Wire on a 3-Way Switch
You can approach identifying each wire in many different ways. First you can use a non-contact voltage tester to find the hot wire by turning the breaker back on for a moment to check each wire for voltage, find the hot wire and label it “hot”, “line”, or “common”.
Next with the breaker off again, you can use a multimeter to look for the two traveler wires.
At the switch location with the wire labeled ‘hot,’ take the other two unlabeled wires and wire nut them together.
Go to the second switch location and set your multimeter to resistance. Your multimeter will read 0.L on any multimeter; this is commonly known as “open loop”, or “over-limit”.
Touch the leads together, and the meter will jump to 0.00 meaning no resistance, or good continuity.
Now remove the three wire nuts from the wires at the second 3-way switch, and find the two wires that move the meter from 0.L to 0.00.
Take those two wires and softly twist them around each other to identify them as potential travelers.
Go back to the first box and remove the two wires you twisted under the same wire nut, making sure there is no copper touching at all between the wires.
Go to the second box and check to see if your multimeter now says 0.L on the two softly twisted wires. If it does, you’ve found your travelers. You can label the last unknown wire switch leg.
Reattach the Wires in the 3-Way Switch
To begin reattaching the wires to the 3-way switch start by identifying the screw on the back of the switch that looks different then the other two screws (hint: it’s usually painted black instead of silver/metallic, or labeled “common”). The black or common screw is the screw that gets the hot wire at the first box and the switch leg wire at the second box. The two traveler wires each land on one of the other silver matching screws at each box. Be sure to tightly fasten each screw with the wire securely underneath.
You can now reinstall the switches and cover plates, turn the breaker back on, and test your newly rewired 3-way switches. When your 3-ways are experiencing the symptoms described at the start, this should absolutely fix the problem.
Need Help? Call OHM!
If all this sounds like a headache and you’re not sure you want to dive into it yourself, just call us at (206) 973-9184 or use our online form. We are happy to help!