How to Wire a Switch Leg for a Light Fixture

Introduction

Installing a switch leg allows you to control a light fixture from a wall switch. This gives you the convenience of turning lights on and off without having to walk directly to the fixture. Wiring a switch leg involves running a 3-wire cable between the switch and the light fixture. The key steps are connecting the hot wire to the switch, the neutral to the fixture, and using the third wire to carry the switched hot back to the light. With proper materials and safe practices, wiring a switch leg can be a straightforward DIY electrical project. In this article, I'll walk through the complete process of wiring a switch leg for a light fixture.

Things You'll Need

Before getting started, make sure you have the following materials:

3-wire NM cable - This provides an extra wire for the switch leg between the fixture and switch. The cable should be 14/2 gauge for 15 amp circuits or 12/2 gauge for 20 amp circuits.
Wire stripper - Used to remove insulation from the ends of the wires.
Voltage tester - Helps verify power is off to the circuit before wiring.
Screwdrivers - For installing switch and connecting wires.
Wire nuts - Twist-on connectors for joining the wires.
Electrical tape - Covers splices and exposed wires.

Turning Off Power

The first step is crucial - make sure the power is OFF to the circuit you're working on. Turn off the appropriate circuit breaker in the main service panel. Then verify power is off by testing outlets along the circuit with a non-contact voltage tester. Working on live circuits can result in electrocution, so this safety step should never be skipped.

Running the Cable

With the power verified off, run the 3-wire NM cable between the light fixture electrical box and the switch box. The best practice is to:

Secure the cable with cable staples every 4-5 feet.
Leave 8-10 inches of extra cable at each box for making connections.
Avoid running parallel with other wires for noise reduction.

Feed the cable through drywall and studs as necessary between the two boxes. Having the right amount of extra wire on each end makes for an easier wiring process.

Wiring the Fixture Box

At the light fixture electrical box, follow these steps:

Cut all three wires, leaving about 8 inches exposed past the sheathing.
Strip 1/2 inch of insulation off the ends of each wire using the wire stripper.
Connect the white (neutral) wire to the other neutral wires inside the fixture box using a wire nut.
Connect the black (hot) wire to the other hot wires feeding the box using a wire nut.
Cap off the red wire with a wire nut by itself for now - this will connect to the switch later.

Make sure all splices are secure and no bare copper is exposed.

Wiring the Switch

At the switch box, connect the wires as follows:

Connect the black (hot) wire from the NM cable to one of the screws on the switch.
Connect the red wire from the NM cable to the other screw on the switch.
Connect the white (neutral) wire from the NM cable to the other neutral wires in the switch box using a wire nut.

This connects the pathway for the switched hot between the switch and light fixture.

Finishing Up

With the wires connected at both boxes, carefully tuck them back inside and seal up any openings with electrical tape. This prevents drafts and protects the connections.

Install the switch and light fixture according to the manufacturers instructions. Typical lights have push-in or screw terminals to secure the wires.

With the boxes sealed up, turn the circuit breaker back on at the service panel. Then test the switch to make sure the light turns on and off properly.

And that completes the process of wiring a basic switch leg for a light fixture! Following proper safety procedures and connecting the wires correctly will lead to many years of trouble-free operation. Let me know if you have any other questions!