To wire a single light, use 14/2 NM-B (Romex) cable on a 15-amp breaker, or 12/2 NM-B on a 20-amp breaker. For a standard installation where power enters the ceiling box first, the incoming black (hot) wire splices to the white wire of the switch-leg cable (re-identified with black tape), while the incoming white (neutral) wire connects directly to the fixture's white wire. At the single-pole switch, the re-identified white wire and the black wire land on the two brass screws, and all bare copper grounds terminate on the green grounding screws.
This guide details the exact NEC-compliant method for wiring a single-pole switch and a single light fixture. We assume a standard US residential 120V nominal system, copper conductors, and the 60°C ampacity column per NEC 334.80 for NM-B cable. Always defer to your local Authority Having Jurisdiction (AHJ) for final code compliance.
Tools, Materials, and Load Specifications
Before pulling any wire, gather the correct materials. Using undersized wire connectors or shallow junction boxes is a primary cause of failed inspections and overheated connections. Here is the exact bill of materials and the electrical specifications for a standard 15-amp lighting branch circuit.
Required Tools and Components
- Wire Strippers: Klein Tools 11055 (calibrated for 14 and 12 AWG solid copper to prevent nicking the conductor).
- Wire Connectors: WAGO 221-412 lever nuts (rated for 32A/600V, accepting 24-12 AWG) or IDEAL 341 wire nuts.
- Voltage Tester: Fluke 117 True-RMS digital multimeter (CAT III rated) and a Greenlee GT-12 non-contact voltage tester for initial screening.
- Cable: Southwire or Cerro 14/2 NM-B with ground.
- Switch: Leviton 1451-W (15A, 120V, single-pole, residential grade).
- Tape: 3M Super 33+ vinyl electrical tape (black) for re-identifying the switched hot conductor.
Load and Box Fill Specifications
| Component | Specification | Rating / Capacity | NEC Reference & Notes |
|---|---|---|---|
| Circuit Breaker | 15A Single-Pole | 1800W max (120V) | NEC 210.3; Standard residential lighting branch |
| Cable | 14/2 NM-B | 15A Ampacity | NEC 334.80; 60°C column limits 14 AWG to 15A |
| Switch Device | Single-Pole 15A/120V | 15A Resistive | NEC 404.14; Must match or exceed circuit rating |
| Ceiling Box Fill | 18.0 cubic inches (min) | 4 conductors + 1 clamp | NEC 314.16; 14 AWG = 2.0 cu in per conductor |
| Switch Box Fill | 14.0 cubic inches (min) | 4 conductors + 1 device | NEC 314.16; Device counts as 2 conductors (4.0 cu in) |
Box Fill Math Example: In the ceiling box, you have two 14/2 cables entering (Power In and Switch Leg). That equals 4 current-carrying conductors (2 blacks, 2 whites). The bare grounds count as a single 2.0 cu in allowance. If using internal cable clamps, they count as one 2.0 cu in allowance. Total: (4 x 2.0) + 2.0 (grounds) + 2.0 (clamps) = 12.0 cubic inches minimum. A standard 4-inch octagonal metal pan box provides 15.5 to 21.5 cubic inches, which is perfectly compliant. For deep-dive box fill calculations, reference the ECM Web box fill guide.
Critical Safety Protocol
Working on branch circuits involves lethal 120V AC potential. Before touching any wire, you must de-energize the circuit at the main service panel. Turn off the 15A or 20A breaker controlling the room. Apply a lockout/tagout device or place tape over the breaker to prevent accidental re-energizing. Never rely solely on a non-contact voltage tester to confirm a circuit is dead. You must verify the absence of voltage using a CAT III rated digital multimeter tested on a known live source (like an extension cord or another live outlet) before and after checking the target wires. For comprehensive electrical safety standards, review the OSHA electrical safety guidelines.
Step-by-Step Wiring Procedure
This procedure uses the 'Power to Light, Switch Leg to Wall' method. This is the most beginner-friendly approach and fully complies with modern NEC requirements (NEC 404.2) to provide a neutral wire at the switch box for future smart switches, without wasting a conductor on 14/3 cable.
Phase 1: Ceiling Junction Box Terminations
- Prepare the Cables: Strip back 3/4 inch of insulation from the ends of all black, white, and red (if applicable) wires using your 14 AWG gauge hole on the wire strippers. Do not nick the copper. Fold the bare copper grounds back temporarily.
- Bond the Grounds: Gather the bare copper ground from the incoming power cable, the bare copper ground from the switch-leg cable, and the green/bare ground pigtail from the metal ceiling box (if metal). Twist them together and secure with a WAGO lever nut or a gray/yellow wire nut. Leave a 6-inch pigtail extending out to connect to the light fixture's green grounding screw later.
- Connect the Neutrals: Take the white (neutral) wire from the incoming power cable and splice it directly to the white (neutral) wire of the light fixture. Secure with a connector. Note: The white wire of the switch-leg cable is NOT used as a neutral here.
- Create the Switched Hot (Switch Leg): Take the black (hot) wire from the incoming power cable and splice it to the white wire of the 14/2 cable running down to the switch. Crucial Step: Wrap both ends of this white wire tightly with black electrical tape to re-identify it as a hot conductor, per NEC 200.7(C)(2).
- Connect the Fixture Hot: Take the black wire from the switch-leg cable (the one returning power from the wall) and splice it to the black (hot) wire of the light fixture.
- Fixture Ground: Connect the bare copper ground pigtail you created in Step 2 to the green grounding screw on the light fixture bracket or canopy.
Phase 2: Wall Switch Box Terminations
- Prepare the Switch Leg Ends: Down at the switch box, strip 3/4 inch of insulation from the black wire and the white (re-identified) wire. Ensure the black tape wraps over the stripped portion slightly so the white insulation is not visible when seated in the terminal.
- Terminate the Ground: Loop the bare copper ground wire clockwise around the green grounding screw on the bottom of the single-pole switch. Tighten firmly. If it is a metal switch box, you must also bond the box with a separate ground pigtail.
- Terminate the Hot Wires: A standard single-pole switch has two brass-colored screws. It does not matter which brass screw gets which wire; the switch simply breaks the continuity between them. Loop the black wire clockwise around one brass screw, and the re-identified white wire clockwise around the other brass screw. Tighten the terminal screws to the manufacturer's torque specification (typically 14 in-lbs for 14 AWG).
- Seat the Device: Carefully fold the wires into the back of the box, pushing the grounds in first, followed by the neutrals (if present), and finally the hots. Mount the switch to the plaster ears and install the cover plate.
Verification and Testing
Never skip the testing phase. A visual inspection cannot confirm internal wire strand breaks or loose terminal bites.
Pre-Power Continuity Test
Before turning the breaker back on, set your multimeter to the continuity setting (the diode/sound wave icon). Place one probe on the black wire at the ceiling box (disconnected from the power source) and the other probe on the black wire at the switch box. Toggle the wall switch. You should hear a beep (near 0.0 ohms) when the switch is ON, and an open loop (OL) when the switch is OFF. This confirms your switch leg is intact and the switch is functioning.
Post-Power Voltage Test
Restore power at the breaker panel. Set your multimeter to AC Voltage (V~).
- Test 1 (Source Verification): Measure between the incoming black and white wires at the ceiling box. Expected reading: 114V to 126V.
- Test 2 (Switched Leg Verification): With the wall switch turned ON, measure between the black switch-leg wire and the white neutral wire at the ceiling box. Expected reading: 114V to 126V.
- Test 3 (Ground Fault Check): Measure between the black switch-leg wire and the bare copper ground. Expected reading: 114V to 126V.
- Test 4 (Neutral-to-Ground Check): Measure between the white neutral wire and the bare copper ground. Expected reading: Less than 2.0V. If this reads 120V, you have a bootleg ground or a severe wiring fault upstream.
If all readings fall within expected thresholds, safely cap any exposed wires, mount the light fixture to the canopy, and install the bulb. For further reading on standard residential wiring practices, consult the National Fire Protection Association (NFPA) NEC resources.
The Most Common Botch: Switched Neutrals
The most frequent and dangerous mistake DIYers make when learning how to wire a single light is 'switching the neutral' instead of the hot conductor. This happens when a builder mistakenly routes the white neutral wire through the switch and splices the black hot wires directly together in the ceiling box.
The Symptom: The light will turn on and off perfectly when you flip the wall switch. To the naked eye, the job looks successful.
The Hazard: Because the hot wire is never broken by the switch, the light fixture's socket remains fully energized at 120V at all times, even when the bulb is dark. If you attempt to change a lightbulb and your finger accidentally brushes the internal metal contact of the socket while you are grounded (e.g., standing on a damp floor or touching a metal ladder), you will receive a severe or potentially lethal shock. NEC 404.2(B) explicitly forbids this practice. Always ensure your switch is interrupting the black (or re-identified white) hot conductor, never the grounded neutral.
