When you are wiring a light switch one way (commonly known as a single-pole switch), you are simply creating a mechanical break in the hot conductor to control a lighting load from a single location. The direct answer for standard US residential wiring is straightforward: the bare or green ground wire lands on the green grounding screw, the white neutral wires are spliced together and bypass the switch entirely, and the two black hot wires (one line, one load) land on the two brass terminal screws. You will need 14 AWG wire for a 15-amp circuit or 12 AWG wire for a 20-amp circuit, paired with a switch rated for 15A or 20A at 120V AC.

Critical Safety Protocol: De-Energize and Verify

⚠️ WARNING: Mains Voltage Hazard

Working inside an electrical box exposes you to 120V AC, which can cause severe shock or fatal electrocution. Never assume a circuit is dead based on the wall switch position or a tripped breaker label.

  • De-energize: Turn off the correct breaker at the main service panel. If possible, apply a lockout/tagout (LOTO) device to prevent accidental re-energizing.
  • Verify Dead: Use a Non-Contact Voltage Tester (NCVT) to check all wires in the box. Follow up with a multimeter set to AC Voltage (V~) probing from the black wire to the bare ground wire. It must read 0.0V before you touch any bare copper. For comprehensive safety practices, always defer to OSHA electrical safety standards and local Authority Having Jurisdiction (AHJ) requirements.

Tools, Materials, and Sizing Requirements

Before opening the wall plate, gather the correct materials. Using undersized wire or mismatched device ratings is a direct violation of National Fire Protection Association (NFPA) NEC guidelines and creates a fire hazard.

Materials List

  • Switch Device: 15A or 20A rated single-pole toggle or rocker switch (e.g., Leviton 1451-2W or Eaton 1201W). Ensure it is UL-listed.
  • Wire Gauge: 14 AWG NM-B (Romex) if the circuit breaker is 15A. 12 AWG NM-B if the circuit breaker is 20A. Never put 14 AWG wire on a 20A breaker.
  • Wire Connectors: UL-listed twist-on wire nuts (e.g., Ideal 341 Orange for 14-12 AWG combinations) or push-in connectors (e.g., Wago 221 series lever nuts).
  • Grounding Pigtail: A 6-inch length of bare 14 AWG or 12 AWG solid copper wire to bond the switch to the ground splice.

Tool List

  • Wire Strippers: Precision strippers with 14 AWG and 12 AWG holes (e.g., Klein 11055) to avoid nicking the copper conductor.
  • Voltage Tester: CAT III or CAT IV Non-Contact Voltage Tester (NCVT) and a True-RMS digital multimeter (refer to Fluke's official multimeter testing guide for proper CAT rating usage).
  • Hand Tools: #2 Phillips screwdriver, flathead screwdriver, and lineman's pliers for twisting ground wires.

Step-by-Step: Wiring a Light Switch One Way

The following steps assume a standard "power at the switch" configuration, where the main feed and the load cable both enter the single-gang switch box.

  1. Strip the Cables and Wires: Strip the outer yellow or white NM-B jacket back about 8 inches from the box edge. Strip exactly 3/4 inch of insulation from the individual black and white conductors. Do not strip the bare copper ground wires unless they are excessively long; they should reach the back of the box and the green screw without excess coiling.
  2. Bond the Grounds (Green/Bare): Gather the bare copper ground wire from the line cable, the bare copper ground wire from the load cable, and your 6-inch bare copper pigtail. Twist them together clockwise with lineman's pliers and secure with an orange wire nut. Wrap the free end of the pigtail clockwise around the green grounding screw on the switch strap and tighten firmly. The switch strap must be bonded to ground to clear faults if the internal mechanism shorts to the metal yoke.
  3. Splice the Neutrals (White): In a standard single-pole setup, the switch does not use the neutral wire. Take the white neutral wire from the line cable and the white neutral wire from the load cable. Strip 3/4 inch, twist them together, and cap them with a wire nut. Push this splice neatly into the back of the box. Note: If you are installing a smart switch or timer that requires a neutral, the white wire will land on the silver terminal marked "Neutral" or "N" on the smart device.
  4. Identify Line vs. Load Hots (Black): Determine which black wire brings power from the panel (Line) and which black wire carries power up to the light fixture (Load). If you are replacing an existing switch, this was marked before removal. If this is a new rough-in, the Line is typically the bottom cable and the Load is the top cable, but you must verify with a voltage tester once power is temporarily restored (safely) or by tracing the cables.
  5. Terminate the Line Hot (Black): Take the identified Line black wire. Form a 3/4-inch hook using your wire strippers. Hook it clockwise around the bottom brass terminal screw on the switch. Tighten the screw until the wire is seated firmly under the screw head and the insulation is just touching the metal strap. Do not over-torque and strip the screw.
  6. Terminate the Load Hot (Black): Take the identified Load black wire and hook it clockwise around the top brass terminal screw. Tighten securely. The mechanical action of the toggle will now bridge or break the connection between these two brass screws.
  7. Fold and Secure: Carefully fold the wires into the box. Push the ground splice to the deep back, followed by the neutral splice, leaving the hot wires folded neatly behind the switch body. Align the switch strap with the box ears and secure it with the provided 6-32 mounting screws. Attach the wall plate.

Verify and Test: Meter Readings & The Most Common Botch

Before declaring the job finished, you must verify the electrical characteristics of the circuit.

Expected Meter Readings

Turn the breaker back on. Keep the wall switch in the OFF position. Set your multimeter to AC Voltage (V~).

  • Line Brass to Ground: Should read ~120V (acceptable range 114V-126V). This confirms power is reaching the switch.
  • Load Brass to Ground: Should read 0V. This confirms the switch is successfully breaking the circuit.
  • Across both Brass Screws (Line to Load): Should read ~120V. This is the potential difference waiting to push current through the lightbulb once the switch closes.

Flip the switch to the ON position. The light should illuminate. The voltage across both brass screws should now drop to near 0V (typically <1V), and the Load Brass to Ground reading should jump to ~120V.

The Most Common Botch: Switching the Neutral

The most dangerous mistake beginners make when wiring a light switch one way is breaking the neutral wire instead of the hot wire, or failing to re-identify a white wire acting as a hot in a "switch loop" configuration.

The Symptom: The light turns on and off perfectly at the wall switch. However, because the hot wire is still continuously connected to the light fixture's socket, the socket remains energized at 120V even when the light is off. If the homeowner attempts to change a lightbulb and accidentally touches the center socket contact, they will receive a severe shock.

The Fix: Always ensure the white wires are spliced together continuously to the fixture, and the black wires are the ones being broken by the brass screws on the switch. If your box only contains one 2-wire cable going up to the ceiling (a switch loop), the white wire coming down is actually your Line Hot. You must wrap it in black electrical tape or use a black marker to re-identify it as a hot conductor before landing it on a brass screw, per NEC 200.7(C)(2).

Frequently Asked Questions

Does it matter which brass screw the hot wire goes on for a single-pole switch?

For a standard, mechanical single-pole AC toggle or rocker switch, it does not matter which brass screw receives the Line hot and which receives the Load hot. AC current alternates direction 60 times a second (60Hz in North America), so the switch simply acts as a bridge. However, if you are installing a smart switch, dimmer, or a switch with a built-in LED locator light, the manufacturer will explicitly label the terminals as "LINE" and "LOAD". In those cases, reversing them will cause the device to malfunction or fail to power its internal logic board.

Can I use a 15A switch on a 20A breaker circuit?

Yes, under specific conditions. NEC Article 404.14(A) permits a 15-amp rated snap switch to be used on a 20-amp branch circuit, provided the switch controls a lighting load that does not exceed 15 amps. Since standard residential LED and CFL lighting loads draw a fraction of an amp, a 15A switch is legally and practically fine on a 20A circuit for lighting. However, if the switch is controlling a dedicated receptacle outlet or a heavy hardwired appliance on that 20A circuit, you must use a 20A rated switch (which features a horizontal slot on the toggle paddle to accept 20A plug prongs).

Why does my light switch have a white wire connected to the brass screw?

If you see a white wire landed on a brass screw, you are looking at a "switch loop" wired with older 2-wire NM cable. In this setup, power goes to the ceiling fixture first, and a single 2-wire cable drops down to the switch. The white wire in that cable is used to carry the continuous hot down to the switch, and the black wire carries the switched hot back up to the fixture. By code, that white wire must be re-identified with black tape or paint at both ends to warn future electricians that it is a hot conductor, not a neutral. If you are replacing the switch, put the re-identified white wire on one brass screw and the black wire on the other.

What is the torque specification for the terminal screws on a standard light switch?

While most standard residential toggle switches do not have strict torque specifications printed on the yoke like high-end commercial spec-grade devices, the general industry standard for 14 AWG and 12 AWG solid copper wire on brass terminal screws is between 12 and 14 inch-pounds. If you do not have a torque screwdriver, tighten the screw until it is snug and the wire cannot be pulled out by hand, then give it an additional quarter-turn. Avoid using power drills with high clutch settings, as stripping the soft brass threads will ruin the switch and create a high-resistance connection that generates excess heat.