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How to Install a Three-Way Switch and Wire a Circuit

Typically used for hallways and staircases, three-way switches are used in instances where two separate switches control one. Use these step-by-step instructions to install a three-way switch and wire a circuit.

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Step 1: Disconnect the Power and Install the Boxes

Tips:

  • For instructional purposes, the main circuit panel is located within this mock bathroom. In a typical residence, the circuit panel would most likely be located in another area.
  • Unless absolutely qualified for system installation, it's recommended that you leave the installation of your home's electrical system to a licensed electrician.
  • Always turn off the power to the circuit before beginning any electrical work.
  • Use a tester to verify the power is disconnected.

Armed with a wiring diagram and the necessary tools, install the boxes that house the switches. According to job specifications, the boxes in this demonstration are hung at 48" from the ground. The boxes come with their own attachment nails, so hammer the boxes into the first available stud from the doorframe.

Note: The metal boxes that house the overhead light and fan have been permanently installed for instructional purposes.

Step 2: Run the Cable

Snake the 14-gauge non-metallic (NM) sheathed cables from the main panel, through pre-drilled holes in the studs and up to the boxes (Image 1). From the boxes, run the cable up and along the joists to the ceiling boxes that house the fan and light.

With the cable in place, fasten it to the framing with brackets called staples, every 4-1/2', at turns and where the cable enters a box (Image 2). Cut the cable to length with linesman pliers, leaving some excess at the boxes for the connections (Image 3). In a typical residential situation, this would complete the "rough-in" stage of the job.

Step 3: Prep and Secure the Ground Wires

Use a cable stripper to slit the cable's plastic insulation and peel it open (Image 1). This exposes the color-coded hot (black/red), neutral (white/yellow) and ground (green/bare) wires within the cable. Trim the peeled insulation with wire cutters.

Before stripping the cables that feed the overhead fixtures, install two-screw cable connectors (Image 2) into the holes called knockouts, out of the boxes. These connectors serve not only to protect the wire, but also to hold them in place.

For this particular box, prepare the ground wires for two switches by fitting a copper crimping sleeve over the three incoming ground wires plus two extra pieces of bare wire (Image 3). Tightly crimp all the wires together using a multi-function stripper (Image 4). To form a good electrical bond, splice the wires by twisting them together with pliers (Image 5). Later, the two extra wires extend to connect to the ground terminals on the switches. For now, the wires are tucked back into the box.

Step 4: Splice the Neutral and Hot Wires

With the ground wires secured, work on splicing the neutral (white) wires. Bundle the three same-colored wires together and uses wire-cutters to trim the ends to an even length. Using wire strippers, strip off a 1" section of insulation from each wire. To splice, hold the three wires together in one hand, while twisting them together with pliers (Image 1). A good rule of thumb when splicing is to keep the insulation end lined up. To complete the splice, screw on a plastic yellow wire nut over the exposed twist of wires (Image 2).

Because there are two switches in this box, but only one incoming hot wire, a pigtail will need to be created to power both switches. By splicing the one incoming wire with two extra pieces of wire (insulated in black to denote "hot") the electricity of two terminals can be channeled. Protect this splice with a yellow wire nut.

Step 5: Connect the Switches to Each Box

With the hot, neutral and ground wires prepared, connect the switches to each box. Loosen the terminal screws with a screwdriver, and then using a hole in the wire stripper, bend the exposed wire into a loop (Image 1). Connect each wire to the correct terminal, orienting the direction of the loop clockwise so that when you tighten the screw, the hooked wire maintains its shape (Image 2). With all connections made, carefully tuck the wires into the boxes, making sure to keep the ground wires separate from any metal or wires, and then screw the switches into the boxes.

Step 6: Wire the Fan and Fixture

Wire the exhaust fan and recessed light fixture. Because the housings are permanently installed, this is merely a matter of splicing like-colored wires. Again, protect the splices with wire nuts.

Step 7: Wire the Circuit Panel and Finish Installation

With the switches and fixtures correctly wired, it's time to wire the main circuit panel. After stripping the incoming cable, connect the neutral and ground wires to their corresponding bus bars. To finish the circuit, connect the hot wire to a circuit breaker, which itself is connected to the panel's hot bus.

Using a volt-ohm meter set to ohms, touch the probes to the various busses on the panel, and then change the position of the three-way switches for another reading. A slight energy reading indicates the circuit is sound.

Screw in the light bulb and plug in the exhaust fan. Flip the main breaker to energize the panel. Before flipping the branch circuit breaker, verify the current using the meter, this time set to volts. With the reading well within perimeters, it's safe to flip on the branch circuit.

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