If you want to control a single light fixture from two different locations—like the top and bottom of a staircase—you are wiring a two-way switch circuit. Before we pull any wire, we must clear up a critical regional terminology trap: in the UK, Europe, and Australia, this is physically called a 2-way switch. In North America, under the National Electrical Code (NEC), the exact same functional circuit uses what are physically called 3-way switches. This guide uses North American NEC standards, 3-way physical devices, and US wire color codes to achieve the two-way functional control you are looking for.

The direct answer for a standard residential setup: You need two 15A 3-way switches, 14/2 NM-B cable from the power source to the first switch, and 14/3 NM-B cable running between the two switches. The black hot wire always lands on the uniquely colored Common (dark) screw, the red and white traveler wires land on the brass screws, and the bare copper lands on the green ground screw.

The Terminology Trap and Component Decision Path

Choosing the wrong switch rating or wire gauge is the most common reason DIYers fail their rough-in inspection. Your wire gauge and switch ampacity must match the breaker protecting the circuit. Under recent NEC cycles, residential lighting circuits are typically protected by a 15-Amp Arc-Fault Circuit Interrupter (AFCI) breaker.

Use this decision matrix to select your exact materials:

Breaker Size Wire Gauge (NM-B) Switch Amp Rating Concrete Part Pick
15 Amp 14 AWG 15 Amp Leviton 5603-2W Decora 15A 3-Way
20 Amp 12 AWG 20 Amp Leviton 5604-2W Decora 20A 3-Way
Default Recommendation: For 95% of modern residential lighting circuits, your concrete pick is 14 AWG NM-B cable and the Leviton 5603-2W 15A switch. Do not mix 14 AWG wire on a 20A breaker, and avoid using 20A switches on 14 AWG wire, as the wire will melt before the switch fails.

Tools and Materials List

Gather these specific tools before opening the panel. Do not substitute a standard voltage tester for a true multimeter when verifying dead circuits.

  • Switches: Two (2) Leviton 5603-2W 15A 3-Way switches (or equivalent 15A 3-way).
  • Cable 1: 14/2 NM-B with ground (Power source to Switch 1).
  • Cable 2: 14/3 NM-B with ground (Switch 1 to Switch 2).
  • Cable 3: 14/2 NM-B with ground (Switch 2 to Light Fixture).
  • Wire Strippers: Rated for 14-12 AWG solid copper (e.g., Klein 11055).
  • Non-Contact Voltage Tester (NCVT): CAT III or CAT IV rated (e.g., Klein NCVT-2).
  • Digital Multimeter: Capable of measuring AC Voltage (V~) and Continuity.
  • Connectors: Purple or yellow wire nuts (Ideal 341 or 368 series) and a green grounding pigtail.
  • Screwdrivers: #2 Phillips and 1/8-inch flathead.

Mains Safety Protocol: De-Energize and Verify

DANGER: LETHAL VOLTAGE. Working on mains wiring (120V AC) carries a risk of fatal electrocution and arc flash. You must de-energize the circuit, lock or tag the breaker, and verify the wires are dead with a tested meter before touching any bare copper. Local codes may require a licensed electrician for this work.
  1. De-Energize: Locate the correct breaker in your main panel and switch it to the OFF position. Place a piece of tape over the breaker with a note reading 'DO NOT TURN ON - WORKING ON CIRCUIT'.
  2. Initial Sweep: Use your Non-Contact Voltage Tester (NCVT) on a known live circuit (like an outlet in another room) to verify the tester's battery is working. Then, test the wires in your switch box. The NCVT should remain silent and unlit.
  3. Verify Dead with Multimeter: Set your digital multimeter to AC Voltage (V~). Place the black probe on the bare ground wire and the red probe on the black (hot) wire. The reading must be exactly 0.0V. Next, test from the black wire to the white (neutral) wire. It must also read 0.0V. Only proceed once you have confirmed zero voltage.

Step-by-Step Wiring: Colors to Terminals

This topology assumes power enters at Switch 1, travels to Switch 2, and then feeds the light fixture. Strip 3/4 inch of insulation from all wires. Ensure no bare copper is exposed outside the terminal connections.

Switch 1 (Power Source Side)

  1. Incoming Hot: Connect the Black wire from the incoming 14/2 power cable to the Common terminal (dark/black screw) on Switch 1.
  2. Traveler 1: Connect the Black wire from the 14/3 cable to the first Brass screw on Switch 1.
  3. Traveler 2: Connect the Red wire from the 14/3 cable to the second Brass screw on Switch 1.
  4. Neutral Pass-Through: Wire-nut the White wire from the 14/2 power cable directly to the White wire from the 14/3 cable. Do not connect these to the switch.
  5. Grounding: Wire-nut the bare copper from the 14/2, the bare copper from the 14/3, and a green grounding pigtail together. Connect the other end of the pigtail to the Green ground screw on Switch 1.

Switch 2 (Load/Light Side)

  1. Traveler 1: Connect the Black wire from the incoming 14/3 cable to the first Brass screw on Switch 2.
  2. Traveler 2: Connect the Red wire from the incoming 14/3 cable to the second Brass screw on Switch 2.
  3. Switched Hot to Light: Connect the Black wire from the outgoing 14/2 cable (heading to the light) to the Common terminal (dark/black screw) on Switch 2.
  4. Neutral Pass-Through: Wire-nut the White wire from the 14/3 cable directly to the White wire from the outgoing 14/2 cable.
  5. Grounding: Wire-nut the bare copper from the 14/3, the bare copper from the 14/2, and a green grounding pigtail together. Connect the pigtail to the Green ground screw on Switch 2.

Light Fixture Termination

  1. Connect the Black wire from the 14/2 cable to the hot (usually black or brass) lead on the light fixture.
  2. Connect the White wire from the 14/2 cable to the neutral (usually white or silver) lead on the light fixture.
  3. Connect the Bare wire to the fixture's grounding screw or green wire.

Verify and Test: Expected Meter Readings

Do not just push the switches into the wall and turn the breaker on. Bench-test the logic first to save yourself a second trip to the panel.

Pre-Power Continuity Test: With power still OFF, set your multimeter to Continuity (the diode/sound icon). Place one probe on the incoming 14/2 Black (hot) wire at Switch 1, and the other probe on the outgoing 14/2 Black (switched hot) wire at Switch 2. Flip the switches. You should hear a continuous beep in exactly two out of four possible switch combinations. If you get a beep in all four or zero combinations, your traveler and common wires are swapped.

Once continuity is verified, tuck the wires neatly into the back of the boxes, mount the switches, and turn the breaker ON. Set your multimeter to AC Voltage (V~) and take these measurements at Switch 2:

  • Common (Dark Screw) to Ground: Should read 120V (nominal 114V-126V) when the light is ON, and 0V when the light is OFF.
  • Brass Screw 1 to Ground: Will read 120V on the active traveler and 0V on the inactive traveler. Flipping Switch 1 will swap which brass screw reads 120V.

Test the physical operation: flip Switch 1, the light toggles. Flip Switch 2, the light toggles. If this works from both locations regardless of the other switch's position, your circuit is correct. For deeper code compliance regarding switch loop identification, refer to the NFPA 70 National Electrical Code Article 404.

The Most Common Botch and Its Symptom

The single most frequent mistake when wiring a two-way (3-way) circuit is swapping the Common terminal and a Traveler terminal. This happens because DIYers assume the physical position of the screws (e.g., 'the single screw on the bottom') dictates the common, rather than looking at the screw color.

The Symptom: The light turns on and off, but the switches act interdependent in a broken, illogical way. For example, Switch A must be in the UP position for Switch B to work. If Switch A is flipped DOWN, Switch B does absolutely nothing.

The Physics of the Failure: A 3-way switch is internally a Single-Pole, Double-Throw (SPDT) mechanism. The Common terminal is the 'pole' (the input or output), and the two brass terminals are the 'throws' (the paths). If you accidentally wire your incoming hot power to a brass 'throw' screw, and wire your travelers to the 'common' and the other 'throw', the circuit can only complete when the internal lever bridges the hot to the common. When you flip the switch the other way, it bridges the hot to the dead-end traveler, killing power to the second switch entirely.

The Fix: Turn the power back off. Pull the switches out. Identify the single wire that is the true line hot (at Switch 1) and the single wire that is the true switched hot (at Switch 2). Ensure these two specific wires are landing only on the uniquely colored dark/black Common screws. The remaining two wires in the 14/3 cable are your travelers and must land on the brass screws. For more on switch terminal identification and safety practices, consult resources like OSHA Electrical Safety guidelines before working on energized panels.

By strictly following the color-to-terminal mapping and verifying your circuit with a multimeter before closing up the wall boxes, you ensure a safe, code-compliant installation that will operate flawlessly for decades. Stick to the 14 AWG and 15A Leviton 5603-2W combination for standard lighting, and never bypass the dead-circuit verification step.