How to Wire a 3 way Light Switch

Step by Step instructions on installing a 3-way light switch

By Mark J. Donovan

A 3-way light switch enables you to control a light from two different locations within a home. For example, at the top and bottom of a stair case, or at two ends of a hallway.

Installing a 3 way light switch on your own can be a little complicated, however once you understand the basic wiring configuration, and follow a few safety rules it is relatively straight forward to do.

Tools required

  • Needle Nose Pliers
  • Screw Drivers
  • Wire Strippers
  • Lineman’s Pliers
  • Carpenter’s Knife

Material Required for Installing a 3-way light switch

  • Romex 12-3 (20 amp) or 14-3 (15 amp) for the traveler wires, depending upon your application and National/Local electrical codes
  • Romex 12-2 or 14-2 for the feed wire.

Note: Romex 12-3 or 14-3 wire has 4 conductors in it, three are sheathed (white/black/red) and one is bare copper (ground). Romex 12-2 or 14-2 wire has 3 conductors in it, two are sheathed (black and white) and one is bare copper.

Always use the same gauge of wire for the entire circuit, either 14-x or 12-x gauge.

  • Two SPDT (single pole double throw) switches
  • Wire Nuts
  • Copper crimp tubes

Working with electricity can be life threatening. Consequently, when installing a 3 way light switch make sure you first turn power off to the feed line that will power the 3 way light switch. The feed line should be turned off at the circuit panel.

Instructions for Installing 3 way Light Switch

Step 1: Run a feed cable to the first light switch from the bottom of the switch box. This is effectively the power feed coming from the circuit panel.

Step 2: Run another cable, known as the traveler between the first switch and the light fixture.

How to Change a Light Switch Ebook

Step 3: Run another traveler cable from the light fixture to the second switch.

Step 4: A three way switch has a common terminal at the bottom and two traveler terminals at the top. Consequently it is wise to have the traveler cables come in from the top of the switch boxes.

Step 5: At the first 3 way switch box, wire the black feed line to the common terminal which is on the bottom right.

Step 6: Next wire the black traveler wire (which is referred to as a “hot” wire since power is running through it) to the top right traveler terminal using a screwdriver.

Step 7: Next wire the red traveler wire (again a “hot” wire) to the left traveler terminal.

Step 8: At the first switch box, attach the 12-3 white wire “neutral wire” to the 12-2 feed neutral wire with wire nuts.

Step 9: Again, at the first switch box, connect the bare copper ground wires together using lineman’s pliers. Twist the copper wires together several times and add a copper crimp tube over them.

Step 10: At the light box, again connect the bare copper ground wires together using lineman’s pliers. Twist the copper wires together several times and add a copper crimp tube over them.

Step 11: At the light box, connect the red wires together with a wire nut.

Step 12: Again, at the light box connect together with a wire nut the black wire coming from the first 3 way switch box, and the white wire coming from the second 3 way switch box. Since you are connecting a black “hot” wire to a white wire that is typically neutral it is important to mark this white wire as now “hot”. To do this, attach a piece of black electrical tape on each end of the white wire that you connected to the black wire.

Step 13: At the second 3 way light switch attach the white wire (with the black tape on it indicating it is now used as a “hot” wire) to the top right traveler terminal.

Step 14: At the second 3 way light switch attach the red wire to the top left traveler terminal.

Step 15: Again at the second 3 way light switch, connect the black wire to the lower right common terminal.

Step 16: Again at the second 3 way light switch, connect together the bare copper ground wires. Twist the copper wires together several times and add a copper crimp tube over them.

Step 17: With the circuit wired up you should be left with at the light box a white wire end (neutral wire) that comes from the first switch box, a black wire (hot wire” that comes from the second switch box, and a bare copper ground wire (associated with the twisted copper wires coming into the light box from the two Romex cables.). These three wires then connect to the light fixture. The ground wire connects to the light chassis, and the black wire end to one of the light fixture terminals, and the white wire end to the other light fixture terminal. Once you have wired the light fixture attach it to the light box.

Step 18: Secure the 3 way switches into their switch boxes and attach face covers.

Step 19: Power up the switch circuit, back at the circuit breaker panel box. Next, test the light. If you followed these instructions perfectly you should have a properly working 3 way light switch.

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