To install a two way light switch (known in the US National Electrical Code as a 3-way switch), you need two 3-way switches, 14/2 NM-B cable for the line and load, and 14/3 NM-B cable for the travelers. The black hot wire lands on the dark common screw, the red and re-identified white wires land on the brass traveler screws, and the bare copper lands on the green ground screw. This guide covers the standard US 120V topology where power enters at the first switch and the load is at the second switch.

Terminology: "Two-Way" vs. "3-Way"

If you are searching for how to install a two way light switch, you are likely using UK, Australian, or European terminology. In those regions, a "2-way" switch controls a single light from two locations. In the United States and Canada, the NEC and CEC refer to this exact same setup as a 3-way switch (because the switch has three current-carrying terminals: one common and two travelers). The instructions below follow US NEC standards, utilizing 120V AC, NM-B (Romex) cable, and US color codes.

Decision Matrix: Switch and Cable Selection

Before opening your electrical panel, you must select the correct hardware. Do not buy standard single-pole switches; they lack the traveler terminals required for this circuit.

Switch Type Best For Pros Cons
Standard Toggle (Leviton 1453-2W) Basements, garages, budget retrofits Cheap (~$1.50), simple internal mechanics Dated look, mechanical snap can wear out
Decora Rocker (Leviton R62-05603-2WS) Living spaces, modern homes, high-use areas Large paddle easy to hit, modern aesthetic, reliable (~$3.50) Requires specific Decora wall plates
Smart Switch (Lutron Caseta PD-5S-DV) Home automation, remote scheduling App control, integrates with Alexa/HomeKit Expensive (~$60+), requires neutral wire and proprietary hub
Default Pick: Buy the Leviton Decora 15A 3-Way Switch (Model R62-05603-2WS). It is rated for 15A/120V AC, features push-in and side-wire terminal options, and the large rocker paddle is vastly superior for high-traffic hallways. Pair it with Southwire 14/3 NM-B (yellow jacket) for 15A circuits.

Tools, Materials, and Device Ratings

Gather these specific items before de-energizing the circuit. Assuming a standard 15-amp lighting circuit:

  • Switches: Two (2) 15A/120V AC 3-way switches (e.g., Leviton R62-05603-2WS).
  • Cable (Line/Load): 14/2 NM-B with ground (Yellow jacket). Rated for 15A max.
  • Cable (Travelers): 14/3 NM-B with ground (Yellow jacket). Contains Black, Red, White, and Bare wires.
  • Wire Nuts/Connectors: Yellow or red wire nuts, or Wago 221-series lever nuts (preferred for solid copper).
  • Electrical Tape: Black electrical tape (mandatory for re-identifying the white traveler wire per NEC 404.2).
  • Testers: Non-Contact Voltage Tester (NCVT) and a CAT III or CAT IV Digital Multimeter.
  • Hand Tools: Wire strippers (with 14 AWG gauge), Phillips #2 screwdriver, flathead screwdriver, lineman's pliers.

Mains Safety Protocol (Do Not Skip)

DANGER: LETHAL VOLTAGE. Working on a 120V AC branch circuit can cause fatal electrocution or arc flash.
  1. Turn OFF the 15A or 20A breaker feeding this lighting circuit at the main service panel.
  2. Apply a lockout/tagout device or place a piece of tape over the breaker with a note: "DO NOT TURN ON - WORKING ON CIRCUIT".
  3. Verify the circuit is dead using an NCVT at the switch box.
  4. Confirm with a multimeter set to AC Voltage (V~): place one probe on the black hot wire and the other on the bare ground. The reading must be 0.0V. Never trust an NCVT alone; always verify with a contact meter.
Note: NEC-style guidance is provided here; your local Authority Having Jurisdiction (AHJ) has final authority. If you are unsure, hire a licensed electrician.

Step-by-Step Wiring: Terminations and Wire Colors

This procedure assumes the Power at Switch 1, Load at Switch 2 topology. Strip all wire ends to exactly 5/8 inch (or use the strip gauge printed on the back of the Leviton switch). Do not leave excess bare copper exposed outside the terminal.

  1. Prepare the Traveler Cable (14/3): At both ends of the 14/3 NM-B cable running between Switch 1 and Switch 2, wrap the white wire with black electrical tape. This re-identifies it as a hot/traveler wire, satisfying NEC Article 404.2 requirements.
  2. Wire Switch 1 (Line Side):
    • Connect the black wire from the 14/2 power cable (coming from the panel) to the dark common screw on Switch 1.
    • Connect the red wire from the 14/3 cable to one of the brass traveler screws on Switch 1.
    • Connect the white wire (with black tape) from the 14/3 cable to the other brass traveler screw on Switch 1.
    • Splice the white neutral from the 14/2 power cable directly to the white neutral of the 14/3 cable (if continuing to the light) or cap it if the light is fed separately. (In this topology, the neutral bypasses the switches).
  3. Wire Switch 2 (Load Side):
    • Connect the black wire from the 14/3 cable to the dark common screw on Switch 2. (This black wire will carry the switched hot up to the light fixture).
    • Connect the red wire from the 14/3 cable to one of the brass traveler screws on Switch 2.
    • Connect the white wire (with black tape) from the 14/3 cable to the remaining brass traveler screw on Switch 2.
  4. Grounding: At both switches, create a pigtail using a short piece of bare 14 AWG copper. Connect the pigtail, the bare wire from the 14/2, and the bare wire from the 14/3 together with a wire nut. Attach the other end of the pigtail to the green ground screw on the switch yoke. If using a metal box, you must also bond the box to the ground wire.
  5. Finalize: Neatly fold the wires into the back of the junction box (push grounds in first, then neutrals, then hots). Mount the switches with the provided 6-32 screws. Do not overtighten; snug is sufficient to prevent stripping the brass yoke threads.

The Most Common Botch (And How to Avoid It)

The Botch: Swapping the Common and Traveler wires. Beginners often connect the incoming hot to a brass traveler screw, and a traveler wire to the dark common screw.
The Symptom: The light behaves illogically. For example, the light will only turn on if Switch A is in the UP position; if Switch A is DOWN, Switch B will not turn the light on at all.
The Fix: Remove the switches and verify the wire mapping. The single incoming hot (or the single outgoing switched hot to the light) must land on the uniquely colored dark/black screw. The two wires from the 14/3 cable must land on the matching brass screws. For more visual references on avoiding this, The Family Handyman's 3-way switch guide provides excellent topology diagrams.

Verify and Test: Expected Meter Readings

Before installing the wall plates and turning the breaker back on, perform a continuity and voltage check to ensure a safe, functional circuit.

  1. Continuity Test (Power OFF): Set your multimeter to Continuity (the diode/beep symbol). Place one probe on the dark common screw of Switch 1 and the other probe on the brass traveler screws. Toggle the switch. The meter should beep on one brass screw in the UP position, and the other brass screw in the DOWN position. Repeat for Switch 2.
  2. Energize: Turn the breaker back ON at the panel.
  3. Voltage Test (Power ON): Set the multimeter to AC Voltage (V~). Place the black probe on a known ground (bare copper) and the red probe on the dark common screw of Switch 2 (the one feeding the light).
    • Expected Reading: When the light is OFF, the meter reads 0.0V. When the light is ON, the meter reads ~120V (acceptable range: 114V - 126V).
  4. Functional Test: Toggle Switch 1 and Switch 2 in all four possible combinations (Up/Up, Up/Down, Down/Up, Down/Down). The light must toggle its state every time either switch is flipped.

Once testing is complete, install the Decora wall plates. For further hardware specifications and wiring diagrams, you can reference the Leviton 3-way switch product documentation. By strictly following the terminal color mappings and re-identifying your white traveler wire, you ensure a code-compliant, safe, and fully functional two-way lighting circuit.