To install a two way light switch (known as a 3-way switch in the US NEC) to control a single fixture from two locations, you need two 15A 3-way switches, 14/2 NM-B cable for the power and load runs, and 14/3 NM-B cable for the traveler run between the switches. The line hot connects to the dark common screw on Switch 1, the red and black travelers connect to the brass screws, and the switched hot returns to the dark common screw on Switch 2.

Global Terminology Note: What the UK, EU, and Australia call a "2-way switch" (terminals COM, L1, L2), the US National Electrical Code (NEC) calls a "3-way switch" (terminals Common, Traveler 1, Traveler 2). This guide uses US NEC 14 AWG color codes and 3-way terminology, but the logical circuit and physical wiring principles are identical. See the terminal mapping table in Step 1 for regional translations.

The Decision Path: Power at Switch vs. Power at Light

Before pulling any cable, you must decide where the main power feed enters the circuit. This dictates your cable routing and wire nut splices. While both methods are code-compliant, one is vastly superior for troubleshooting and future modifications.

Scenario Cable Routing Pros Cons Verdict
Power at Switch 1 14/2 to SW1, 14/3 to SW2, 14/2 to Light Easiest to troubleshoot; keeps neutrals simple; standard new-construction method. Requires pulling 14/3 between switch boxes. DEFAULT PICK
Power at Light Fixture 14/2 to Light, 14/3 to SW1, 14/2 to SW2 Useful for retrofitting ceiling fans where power is already at the canopy. Requires re-identifying white wires as hot; complex neutral routing. Avoid unless retrofitting.

The Concrete Pick: Always route Power at Switch 1 unless you are trapped by existing retrofit constraints. It keeps the neutral wire continuous and untouched through the switch loop, which is now a strict requirement under NEC Article 404.2(C) for smart switch compatibility.

Tools, Materials, and Device Ratings

Do not substitute 15A devices on a 20A breaker circuit. Match your device rating to your branch circuit breaker and wire gauge.

  • Switches: Two 15-Amp, 120V 3-way switches (e.g., Leviton Model R62-05603-2WS or Eaton 1873).
  • Cable: Southwire 14/2 NM-B (with ground) and 14/3 NM-B (with ground). Note: If on a 20A circuit, upgrade to 12 AWG wire and 20A switches.
  • Wire Strippers: Klein Tools 11063 (strips 10-20 AWG solid/stranded without nicking copper).
  • Multimeter: Fluke 117 True-RMS (CAT III 600V rated) with non-contact voltage (NCV) detection.
  • Connectors: IDEAL WingNut 341 (purple) or 332 (yellow) for 3-wire splices; 3M Scotchlok for grounds.
  • Torque Screwdriver: Set to 14 in-lbs (standard for 14 AWG terminal screws).

Mains Safety and Verification Protocol

DANGER: LETHAL VOLTAGE. Working on branch circuits involves 120V AC, which can cause fatal ventricular fibrillation. You must de-energize the circuit at the main panel, apply a physical lockout/tagout device to the breaker, and verify the circuit is dead with a tested meter before touching any bare copper. Local codes may require a licensed electrician for new circuit runs.
  1. Turn off the specific 15A or 20A breaker controlling the light at the main service panel.
  2. Place a lockout tag or physical breaker lock on the panel door.
  3. Use the Fluke 117 NCV sensor to scan the existing switch faceplate. Listen for the continuous tone to cease.
  4. Remove the switch cover and test contact voltage: place the black probe on the bare ground wire and the red probe on the black line hot. The meter must read 0.00V.

Step-by-Step Wiring: Power at the First Switch

The following steps assume the "Power at Switch 1" routing method. Strip all wire insulation to exactly 3/4 inch (19mm) using your wire strippers. Form a clockwise J-hook on solid wires for terminal screw connections.

Regional Terminal Mapping:
US Common (Dark Screw) = UK/AU COM
US Traveler 1 (Brass Screw) = UK/AU L1
US Traveler 2 (Brass Screw) = UK/AU L2
US Black Wire = UK Brown (Line) / US Red Wire = UK Blue (Traveler)

Switch 1 (Line Side / Power Feed)

  1. Grounds: Connect the bare copper ground from the 14/2 power feed, the bare copper from the 14/3 traveler cable, and a 6-inch bare copper pigtail together using a wire nut. Connect the other end of the pigtail to the Green Ground Screw on Switch 1.
  2. Neutrals: Splice the white (neutral) wire from the 14/2 power feed directly to the white (neutral) wire of the 14/3 traveler cable using a wire nut. Do not connect any white wires to the switch itself. Push this splice to the back of the box.
  3. Line Hot: Connect the black (hot) wire from the 14/2 power feed to the Dark Common Screw on Switch 1. Tighten to 14 in-lbs.
  4. Travelers: Connect the black and red wires from the 14/3 traveler cable to the two Brass Traveler Screws on Switch 1. (Order does not matter between the two brass screws).

Switch 2 (Load Side / Light Fixture Feed)

  1. Grounds: Connect the bare copper ground from the 14/3 traveler cable, the bare copper from the 14/2 load cable, and a 6-inch bare copper pigtail. Connect the pigtail to the Green Ground Screw on Switch 2.
  2. Neutrals: Splice the white wire from the 14/3 traveler cable directly to the white wire from the 14/2 load cable. Push to the back of the box.
  3. Switched Hot (Load): Take the white wire from the 14/2 load cable going up to the light fixture. Wrap it with black electrical tape at both ends to re-identify it as a hot wire. Connect this taped white wire to the Dark Common Screw on Switch 2.
  4. Travelers: Connect the black and red wires from the 14/3 traveler cable to the two Brass Traveler Screws on Switch 2.

The Light Fixture

  1. Ground: Connect the bare copper ground from the 14/2 load cable to the fixture's green ground screw or grounding pigtail.
  2. Neutral: Connect the white wire from the 14/2 load cable to the fixture's white/neutral wire.
  3. Hot: Connect the black-taped white wire (switched hot) from the 14/2 load cable to the fixture's black/hot wire.

The Most Common Botch (And How to Fix It)

The Symptom: The light turns on and off normally when Switch 1 is in the "UP" position. However, when Switch 1 is flipped "DOWN", the light turns off, and Switch 2 becomes completely dead (flipping Switch 2 does nothing).

The Cause: The Line Hot wire was mistakenly landed on one of the Brass Traveler screws instead of the Dark Common screw on Switch 1. Because the travelers only carry current when the internal toggle bridges the common to that specific traveler, putting the power feed on a traveler means half the circuit is dead whenever the switch toggles away from that specific brass terminal.

The Fix: De-energize the circuit. Pull Switch 1 out of the box. Identify the wire carrying continuous 120V from the panel (using your multimeter once power is briefly restored for testing, then killed again). Move that specific wire to the isolated Dark Common screw. The brass screws are strictly for the 14/3 red and black traveler wires.

Verify and Test: Expected Multimeter Readings

Never assume the circuit is correct just because the light turns on. Verify the integrity of the wiring with these specific measurements before pushing the devices back into the drywall boxes.

  1. Line Voltage Check: With the breaker ON and switches removed (wires safely separated), set your Fluke 117 to VAC. Place the red probe on the 14/2 black line hot and the black probe on the bare ground. Expected reading: 120V (114V-126V is the acceptable ANSI C84.1 range).
  2. Traveler Continuity Check: Turn the breaker OFF. Set the multimeter to Continuity (the diode/sound wave symbol). Place probes on the red and black wires of the 14/3 cable at Switch 2. Flip Switch 1. You should not have continuity between red and black (they are isolated paths). Place one probe on the Switch 1 Common wire and the other on a Switch 2 Traveler wire. Flip the switch; continuity should make and break. This confirms the internal mechanical contacts are functioning.
  3. Load Voltage Check: Restore power. Set meter to VAC. Measure between the switched hot (taped white wire) and the neutral at the ceiling box. With switches toggled to "ON", expect 120V. With switches toggled to "OFF", expect 0V.
  4. Ground Fault Check: Measure between the switched hot and the bare ground at the ceiling box. Expect 120V when ON. If you read 0V here but 120V on the neutral test, your ground path is broken or you have a floating neutral.

For further reading on NEC compliance regarding switch loops and neutral requirements, refer to NFPA's National Electrical Code resources. For proper multimeter safety categories and testing procedures, consult the Fluke electrical testing safety guides.