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How to Wire a Light Switch: Single-Pole Switch Wiring for Beginners (2026)

Wiring a single-pole light switch is one of the most common DIY electrical jobs. This guide covers identifying the hot wire, connecting the switch, and wiring to code — including the neutral and ground requirements.

Quick Answer

Wire a single-pole light switch: (1) Turn off the circuit breaker and verify no voltage with a non-contact tester. (2) A single-pole switch interrupts the hot wire (black) only — both wires on the switch are hot or switch legs. Connect one black wire to each brass screw. The green screw gets the bare copper ground wire. (3) If both wires in the box are white: one is the 'switch leg' return wire, marked with black tape to indicate it carries hot voltage. Connect marked (black tape) white wire to one brass screw, the other wire to the second screw. (4) Never connect the neutral (white) to the switch — the switch interrupts hot only.

Frequently Asked Questions

What is a single-pole light switch and how does it work?

Single-pole switch basics: (1) A single-pole switch has two brass (or gold) terminal screws, one green screw (ground), and a toggle that reads ON/OFF. It is the most common residential light switch — controls a light from one location only. (2) Electrically, it is a simple open/close device wired in series with the hot (black) wire to the light. When the switch is ON: the circuit is complete and power reaches the light fixture. When OFF: the hot wire is interrupted, the circuit is open, and the fixture is de-energized. (3) The neutral (white) wire does not pass through the switch — it runs directly from the panel to the light fixture. The switch only handles the hot. (4) Switch loops: in older wiring, the power enters at the light fixture box first, then a two-wire cable (black and white) runs from the fixture down to the switch box. Both wires in this switch box are hot — there is no neutral at the switch. One wire brings hot voltage down from the fixture, the other returns switched hot back up to the fixture. This is called a switch loop. (5) Modern code (NEC 2011+): requires a neutral wire to be present at all switch boxes in new construction, even if not currently used. This allows future smart switches that require a neutral. Older homes with switch loops are grandfathered.

How do I identify the wires in a switch box?

Switch box wire identification: (1) Standard power-to-switch configuration (power enters the switch box): you will have a black wire (hot from panel), a white wire (neutral to fixture), and a bare copper or green wire (ground). Connect black to one brass screw, the other brass screw gets the wire going to the fixture (also usually black). White goes to the neutral connector (wire nut). Ground to green screw. (2) Switch loop configuration (power enters the light box first): both wires in the switch box are from the same cable. One white and one black (or two whites, or two blacks — varies by age). Neither is a true neutral. Mark the white wire with black electrical tape to indicate it is hot. Connect it to one brass screw; connect the other wire to the second brass screw. (3) How to tell which is which: with power OFF, use a non-contact voltage tester at the switch box with just the circuit breaker on. If one wire is hot and the other is not (dead): the hot wire goes to one screw, the other wire (which will be hot when the switch is ON) goes to the other screw. (4) Non-contact tester: essential tool for this work. Costs $15–$25. Never assume power is off based on the switch position alone — always test before touching wires.

How do I replace a light switch step by step?

Light switch replacement procedure: (1) Turn off the circuit breaker for the circuit. Use a non-contact tester to confirm voltage at the switch box is off — test with the switch in both ON and OFF positions. (2) Remove the switch plate screws, pull the switch out of the box carefully. The switch is attached to two wires. (3) Take a photo of the existing connections before disconnecting. (4) Loosen the terminal screws and remove the wires, or use a small flathead screwdriver to depress the release holes on push-in (backstab) connections. (5) Do not reuse backstab connections on the new switch. Connect wires under the screw terminals — loop the wire clockwise so tightening the screw draws the loop closed. (6) Connect wires to the new switch: typically black (or marked white) to each brass screw, bare copper to the green screw. The switch is not polarity-sensitive — either black wire can go to either brass screw. (7) Fold the wires back into the box, push the switch into the box, fasten the mounting screws, install the plate. (8) Restore power and test the switch. (9) NEC code: the device must be mounted in a code-approved electrical box. Do not install a switch without a box.

How do I add a switch to a light that has no switch?

Adding a new switch to an unswitched light: (1) This requires running a new cable from the switch box location to either the light fixture or the existing power source. The circuit path determines the cable run. (2) If power can be brought to the new switch box first: run 14/2 (15A circuit) or 12/2 (20A circuit) cable from the nearest outlet or junction box that has power. At the light, connect the switch leg to the hot and run the switched hot to the fixture. (3) If you can access the attic or basement: run the cable through the framing using a flex drill bit, which avoids cutting drywall. For inside walls: use fish tape or glow rods (see our wire fishing guide). (4) The new switch box must be at standard switch height (48 inches from finish floor to center of box) and accessible — cannot be behind furniture or inside a closet. (5) All new work must be inspected by local code authority in most jurisdictions — pull a permit for switch additions in habitable rooms. (6) Homeowners are permitted to pull permits for their own homes in most states — the permit process ensures the work meets code and protects the home value.

What are the differences between a single-pole and 3-way switch?

Single-pole vs. 3-way vs. 4-way switches: (1) Single-pole switch: two brass screws, one location controls the light. The toggle has ON/OFF markings. (2) 3-way switch: three screws — one black (common) screw and two brass (traveler) screws. No ON/OFF markings. Used in pairs when you want to control a light from two locations (top and bottom of stairs, either end of a hallway). Both switches in a 3-way circuit must be 3-way switches. (3) 4-way switch: four brass screws, no common. Used in the middle of a 3-way circuit to add a third control location. A circuit with three control points needs two 3-way switches (at each end) and one 4-way switch (in the middle). (4) Identifying which switch you have: a single-pole has 2 screws + ground. A 3-way has 3 screws + ground. A 4-way has 4 screws + ground. The old switch is the guide — always replace with the same type. (5) Smart switches: most smart switches (Lutron Caseta, Leviton Decora Smart) require a neutral wire. In a switch loop location (no neutral), you need a smart dimmer that doesn't require neutral (specific models exist) or you must run a new cable with a neutral.

Wire a single-pole light switch: (1) Turn off the circuit breaker and verify no voltage with a non-contact tester. (2) A single-pole switch interrupts the hot wire (black) only — both wires on the switch are hot or switch legs.

Connect only the black wires to the switch brass screws — the white neutral bypasses the switch entirely and goes straight to the fixture.

What you need

Step 1: Cut power and verify

Turn off the circuit breaker. Test at the switch box with the non-contact tester. Confirm dead in both ON and OFF positions.

Step 2: Remove the old switch and photograph the wiring

Remove the plate and switch. Photo the connections. Loosen terminal screws or push release tabs to free the wires.

Step 3: Connect to the new switch

One black wire to each brass screw (tighten clockwise loop). Bare copper to the green ground screw. If white wires are present, mark hot whites with black tape and treat as black.

Step 4: Install and test

Fold wires into the box, seat the switch, fasten the mounting screws, install the plate. Restore power and test.

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  1. Cut power and verify no voltage

    Turn off the circuit breaker for the circuit. Use a non-contact voltage tester at the switch box with the switch in both ON and OFF positions to confirm no voltage is present. Never skip the tester — a switch in the OFF position does not mean the circuit is dead.

  2. Remove the old switch and photograph wiring

    Remove the switch plate screws and pull the switch out of the box. Take a clear photo of the existing wire connections before disconnecting anything. Loosen the terminal screws to free the wires, or press a small flathead screwdriver into the release holes on backstab connections to release them.

  3. Connect wires to the new switch

    Connect one black wire to each brass screw (loop wire clockwise so tightening the screw draws the loop closed). Connect bare copper or green ground wire to the green screw. If white wires are present in a switch loop configuration, mark the hot white with black electrical tape and treat it as a black wire. Do not use backstab connections — use the screw terminals.

  4. Install switch and test

    Fold the wires back into the box and push the switch in. Fasten the mounting screws evenly. Install the cover plate. Restore power at the breaker and test the switch in both positions. If the light doesn't respond, turn off power again and re-verify connections.

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