Installation of Two Light Switches in One Box

Add a separately switched light.

There are many situations where adding a second switch in an existing electrical junction box may be useful. Sometimes there is not enough room to add another junction box or even to replace a single-gang box with a double-gang box. Other times, adding a second switch for a ceiling or exhaust fan or another light circuit in an existing room may be problematic, especially if the walls are concrete or CMU (Concrete Masonry Unit) construction. Regardless, installing two light switches in a single box most often requires less work than installing a new junction box. Installing two light switches in one box can be completed in a few simple steps.

Things You'll Need

• Combination double single-pole light switch
• NM sheathed wire cable (3 conductor, gauge to match existing)
• Wire clippers
• Needlenose pliers
• Wire stripper pliers
• Screwdrivers (insulated flathead and Phillips bit)
• ½-inch auger drill bit
• Electric drill motor
• Wire nuts

Instructions

1. Locate the circuit powering the switch and open the breaker to effectively turn off the circuit. Always turn power off at the main electrical panel before working on any circuits. See additional safety warnings below.

2. Remove the existing single-pole toggle switch from the electrical box. It's assumed that the box is fed by a single branch circuit from the panel (12- or 14-gauge, 3-wire, non-metallic (NM) sheathed cable), and an additional 3-wire NM cable enters the box that leads to the existing light fixture(s). Use a screwdriver to loosen the screws on the sides of the switch to disengage the wires before removing the switch. Mark the wires with some removable tape to keep track of which cable is coming from the panel and which is going to the light fixture. The black (hot) wire connected at the bottom of the switch is usually the feed from the panel.

3. Run a new 3-wire (gauge to match existing) NM cable to the electrical box from your new light fixture. Remove a portion of the wall finish above the electrical box and near the ceiling so you can fish the new NM cable through the top plate from the attic, down the wall and into the existing box. At least ¼ inch of outer sheathing must penetrate to the inside of the box. Leave about 6 inches of wire slack inside the box. Use an auger drill to create a hole in the framing top plate to allow the NM cable to reach into the attic.

4. Wire the new double switch. The combination double switch has two switches. In most cases the switch will be configurable between switching two devices from a single circuit (as in our case) or by separately switching two circuits.

5. Using a wire nut, reconnect all of the bare ground wires. Include the ground wire from the newly introduced NM cable.

6. Using a wire nut, connect all of the white (neutral) wires together.

7. Connect the black (hot) feed wire to the feed terminal on the double switch. This is usually the screw terminal that has a removable tab connecting it to the adjacent screw terminal. Follow the wiring diagram included with the switch.

8. Connect the remaining two black wires that lead to the fixtures (existing and new) to the opposite screw terminals on the switch.

9. Bend the wires back into the box and screw the switch onto the box. Think "Z" bend when you are pushing the wires back in.

10. Patch the wall finishes to original condition.

11. Screw the switch plate over the switch to complete the work.

Tips & Warnings

• Wiring of new devices are not specifically covered in this article. Be sure to complete all wiring to all devices prior to reenergizing any circuits.

• Always seek assistance from a licensed electrician.

• Before beginning any electrical work, turn off the power at the main electrical panel, fuse box or breaker box. If there is any uncertainty about which circuit you are working on, you can remove the main fuse or trip the main breaker.

• Use only UL listed parts and devices.