Installation Of Two Light Switches In one Box
There are a lot of situations where adding a second switch in an existing electrical junction box may be useful. Sometimes there shouldn’t be 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 could also be problematic, especially if the walls are concrete or CMU (Concrete Masonry Unit) construction. Regardless, installing two light switches in a single box most frequently requires less work than installing a brand new junction box. Installing two light switches in a single box may be completed in just a few simple steps.
Things You may Need
Combination double single-pole light switch
NM sheathed wire cable (3 conductor, gauge to match existing)
Wire stripper pliers
Screwdrivers (insulated flathead and Phillips bit)
½-inch auger drill bit
Electric drill motor
Locate the circuit powering the switch and open the breaker to effectively turn off the circuit. Always turn power off at the primary electrical panel before working on any circuits. See additional safety warnings below.
Remove the present single-pole toggle switch from the electrical box. It is 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 a further 3-wire NM cable enters the box that results in the present 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 sunshine fixture. The black (hot) wire connected at the underside of the switch is usually the feed from the panel.
Run a new 3-wire (gauge to match existing) NM cable to the electrical box out of your new light fixture. Remove a portion of the wall finish above the electrical box and near the ceiling so you may fish the new NM cable through the highest plate from the attic, down the wall and into the prevailing box. No less than 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 within the framing top plate to permit the NM cable to achieve into the attic.
Wire the brand new double switch. The mix double switch has two switches. In most cases the switch might be configurable between switching two devices from a single circuit (as in our case) or by separately switching two circuits.
Using a wire nut, reconnect all the bare ground wires. Include the bottom wire from the newly introduced NM cable.
Using a wire nut, connect all of the white (neutral) wires together.
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.
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Connect the remaining two black wires that result in the fixtures (existing and new) to the other screw terminals on the switch.
Bend the wires back into the box and screw the switch onto the box. Think “Z” bend if you end up pushing the wires back in.
Patch the wall finishes to original condition.
Screw the switch plate over the switch to complete the work.
Tips & Warnings
Wiring of latest devices aren’t specifically covered in this article. Be sure to finish all wiring to all devices previous to reenergizing any circuits.
Always seek assistance from a licensed electrician.
Before beginning any electrical work, turn off the ability 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 primary breaker.
Use only UL listed parts and devices.