If you need to add a switched overhead light and a receptacle to a single-gang box, a switch/outlet combo device is the most efficient solution. The direct answer: For a standard 15-amp residential branch circuit, use a 15A-rated combo device (such as the Leviton 5243) wired with 14 AWG copper conductors. The incoming black (hot) wire lands on the brass terminal, the white (neutral) wire lands on the silver terminal, the bare copper (ground) lands on the green terminal, and the black or red (switch leg) wire lands on the second brass terminal. If your circuit is rated for 20 amps, you must step up to 12 AWG wire and a 20A-rated combo device with a T-slot receptacle face.
This guide walks through the most common configuration: an always-hot receptacle with a switch that controls a separate remote light fixture. We will cover exact terminal mappings, torque specifications, and the testing sequence required to ensure the installation is safe and code-compliant.
Tools, Materials, and Device Ratings
Do not start this job until you have the correct materials on your workbench. Using a 15A device on a 20A breaker is a direct violation of NEC 210.21(B)(3) and a fire hazard.
- Device: Leviton 5243-W (15A) or Leviton 5245-W (20A) switch/outlet combo.
- Wire: 14 AWG NM-B (for 15A circuits) or 12 AWG NM-B (for 20A circuits). Copper only.
- Breaker: 15A or 20A single-pole, matching the wire gauge.
- Wire Strippers: Klein Tools 11055 (for precise 5/8-inch stripping without nicking the copper).
- Torque Screwdriver: Klein Tools 690 or similar, calibrated to inch-pounds.
- Testers: Non-contact voltage tester (NCVT) and a digital multimeter (DMM) with CAT III rating.
- Connectors: Ideal 33 or 34 wire nuts, or Wago 221 lever nuts for pigtailing.
Mains Safety and Prep
Working on branch circuits involves 120V AC mains voltage, which can cause fatal electrocution or arc flash. You must de-energize the circuit at the main breaker panel before opening the junction box. Place a piece of tape over the breaker to prevent accidental re-engagement (lockout/tagout). Never rely solely on a wall switch to de-energize a box. Always verify the circuit is dead using a tested NCVT and a multimeter before touching any bare conductors. Local AHJ (Authority Having Jurisdiction) codes may require a licensed electrician for new circuit runs or panel work.
Terminal Mapping and Wiring Steps
Before stripping wires, understand the physical layout of the combo device. The hot side (brass screws) features a small metal break-off fin between the two screws. For an always-hot outlet and a switched remote light, leave this brass fin intact. This allows the single incoming hot wire to feed both the receptacle and the switch internally.
| Wire Color | Function | Terminal Screw | Device Marking |
|---|---|---|---|
| Black | Line (Incoming Hot) | Brass (Either) | LINE / Hot |
| Black or Red | Load (Switch Leg to Light) | Brass (The other) | LOAD |
| White | Neutral | Silver | Neutral / White |
| Bare / Green | Equipment Ground | Green | GRD / Ground |
Step-by-Step Installation
- Identify and Prep Wires: Using your NCVT and multimeter, confirm the box is dead. Identify the Line (incoming hot), Neutral, Ground, and Load (wire running to the light fixture). Strip exactly 5/8 inch of insulation from each conductor. Do not nick the copper.
- Terminate the Ground: Form a J-hook in the bare copper ground wire. Loop it clockwise around the Green ground screw at the bottom of the device. Tighten to 14 inch-pounds. If the metal box is grounded, pigtail the device ground to the box ground using a wire nut.
- Terminate the Neutral: Hook the white neutral wire clockwise around the Silver terminal screw. If there are multiple neutral wires in the box (e.g., feeding downstream), pigtail them together with a wire nut and run a single white pigtail to the silver screw. Tighten securely.
- Terminate the Line (Hot): Hook the incoming black hot wire clockwise around one of the Brass terminal screws. Ensure the break-off fin between the two brass screws is intact. Tighten the screw.
- Terminate the Load (Switch Leg): Hook the black or red wire running up to the light fixture clockwise around the remaining Brass terminal screw. This completes the switch loop.
- Seat the Device: Carefully fold the wires into the back of the single-gang box. Push the device flush against the drywall or plaster ring. Drive the top and bottom mounting screws into the box ears, alternating turns to keep the device level. Torque mounting screws to prevent cracking the yoke.
Verify and Test Sequence
Do not skip the verification step. A miswired combo device can energize the light fixture shell or trip a GFCI upstream.
- Visual Inspection: Ensure no bare copper is visible outside the terminal saddles, and no insulation is trapped under the screw heads.
- Energize: Remove the breaker tape and flip the 15A/20A breaker to the ON position.
- Receptacle Test: Plug a standard receptacle tester (like the Klein Tools RT210) into the bottom outlet. It should read 'Correct Wiring' (two yellow lights, one dark). Alternatively, use your DMM: measure between the hot slot (short side) and neutral slot (long side). You should read 114V to 126V AC. Measure between neutral and the U-shaped ground slot; it should read less than 2V.
- Switch Test: With the switch in the OFF position, measure voltage at the light fixture canopy (if accessible) or verify the light is off. Flip the switch ON. The light should illuminate. Measure voltage across the switch terminals; it should read 0V when ON (closed circuit) and 120V when OFF (open circuit).
The Most Common Botch: The Switched Neutral
The most dangerous mistake DIYers make when wiring a light switch outlet combo in older homes is the 'Switched Neutral' or 'Bootleg Switch'. This happens when the incoming hot wire is wired directly to the light fixture, and the white neutral wire is run down to the switch box to act as the switch leg.
The Symptom: The light turns on and off perfectly, and the outlet works. However, when the switch is turned OFF, the light fixture shell remains energized at 120V. If you change a bulb and touch the metal threads inside the socket, you complete the circuit to ground and receive a shock.
The Fix: The switch must always interrupt the ungrounded conductor (the black hot wire). If you open a box and find a white wire connected to a brass switch terminal, it is being used as a switch leg. Per NEC Article 200.7(C), this white wire must be permanently re-identified with black tape or marker at both ends to indicate it is a hot conductor, not a neutral. If the wiring is entirely reversed (switching the neutral), you must rewire the circuit so the hot leg hits the switch first.
Frequently Asked Questions
Can I wire a light switch outlet combo without a neutral wire?
No. Unlike smart switches that can sometimes operate on a ground or via a bypass capacitor, the receptacle half of a combo device absolutely requires a dedicated neutral (white) wire to complete the 120V circuit for whatever you plug into it. Furthermore, NEC 404.2(C) has mandated since the 2011 code cycle that a neutral conductor must be present at nearly all switch locations to accommodate future smart devices or combo receptacles. If your older switch box only has a 2-wire cable (black and white, where white is used as a switch leg), you cannot install a combo device without pulling a new 3-wire cable (with a true neutral) from the light fixture or upstream junction box.
How do I make the switch control the built-in outlet instead of a remote light?
If your goal is to have the toggle switch turn the bottom receptacle on and off (common for garbage disposals or workshop tools), the wiring changes slightly. You will need to use a pair of needle-nose pliers to break off the brass fin connecting the two brass screws. Wire the incoming hot (black) to the brass screw designated for the switch. Leave the other brass screw empty. Wire the neutral and ground as normal. When you flip the switch, it will route power to the receptacle. Note: Some manufacturers sell dedicated 'switch-controlled outlet' combo devices (like the Leviton 5241) where this internal routing is pre-configured, saving you the trouble of breaking the tab.
Why is my switch outlet combo getting warm to the touch?
A combo device should never feel hot. If it is warm, you likely have one of three issues: 1) Overloading: You are pulling more than 12A continuous through a 15A device (remember the 80% continuous load rule). 2) Backstabbing: You used the push-in back-wire holes instead of wrapping the wire around the terminal screws. Backstab connections rely on a tiny spring clip that loosens over time, creating high resistance and heat. Always use the side terminal screws. 3) Loose Torque: The terminal screws were not tightened to the manufacturer's spec (usually 14 in-lbs). Use a torque screwdriver to ensure a gas-tight connection.
What size breaker and wire gauge do I need for a 20A switch outlet combo?
If you are installing a 20A-rated combo device (which features a T-slot neutral receptacle face to accept NEMA 5-20P plugs), the circuit must be protected by a 20A breaker and wired entirely with 12 AWG copper wire. Do not mix 14 AWG wire on a 20A breaker, even if the device itself is rated for 20A. The breaker protects the wire, not the device. If 14 AWG wire is present anywhere in the branch circuit, the breaker must be downgraded to 15A, and you must use a 15A combo device.
