How to Install a Light Fixture With Three Wires
A three-wire light fixture circuit -- more commonly referred to as a three-way switch -- allows a single light fixture to be controlled by a pair of switches. This setup is particularly useful in rooms with a main light fixture and two entry points. Wiring a three-way switch is not difficult but is a departure from the standard power supply-fixture-switch circuit. In addition to the standard wiring pattern, it involves power-carrying “traveler wires” linking the two switches.
Locate a circuit capable of supporting the power flowing to the new fixture. A standard 15-amp household circuit is capable of carrying 1,440 watts of power, so make sure the new fixture will not cause the circuit to draw more than that.
Make the cuts in the wall and ceiling for the switches and fixture. Above the switches, where the wall meets the ceiling, make 1x2-inch holes to make threading the cable easier. Save the drywall from these holes to replace at the end of the job.
Install the switch boxes and the fixture junction box. Switch boxes can be attached to drywall, but the fixture box may have to be suspended from a brace bar between two ceiling joists depending on the size and weight of the fixture.
Run three-wire NM cable rated for the circuit (most likely 14-gauge). First run the cable from the first switch to the fixture box and a second cable from the fixture box to the second switch.
Kill power to the circuit.
Make the wire connections at the fixture junction box. Connect the ground wires together and ground to the fixture box. Connect the red, “traveler” wires together. Connect the black wire from the first switch to the white wire of the second switch and wrap a piece of electrical tape around the white wire to indicate it is hot. A single white (neutral) wire from the first switch and one black (hot) wire from the second remain to be connected to the light fixture.
Connect the wires at the first switch. Connect the power supply black wire to the common terminal on the switch (it is labeled as such). Attach the black and red traveler wires to the other terminals. Connect the white wire from the power supply to the white wire from the light fixture.
Connect the wires at the second switch. Attach the red and white wires (remember this is the hot white wire) to the non-common terminals. Wrap a piece of black electrical tape around the white wire to indicate it is hot. Connect the black wire to the common terminal.
Complete the connections by attaching the black and white wires at the fixture box to the light fixture. Affix the fixture to its junction box.
Things You Will Need
- Utility knife or keyhole saw
- Two light switches
- Two switch boxes
- Fixture junction box
- Fixture brace bar (optional)
- NM 3-wire electrical cable
- Electrical connectors
- Electrical tape