A 2-way light switch allows you to control a single lighting fixture from two separate locations—typically at the top and bottom of a staircase or at dual entrances to a room. If you are wiring this in the UK, Australia, or New Zealand, you will use a 2-way switch with COM, L1, and L2 terminals. If you are in the US or Canada, this exact same setup is called a 3-way switch, utilizing Common and two Traveler terminals. Regardless of your region, the core principle is identical: a permanent live feed enters the first switch, two "strappers" (or travelers) bridge the two switches, and a switched live exits the second switch to the light fixture. This guide details the exact terminal mapping, cable gauges, and step-by-step terminations to get your circuit working safely on the first try.
Working with mains electricity (230V AC in UK/AU/EU, 120V AC in US/CA) carries a risk of fatal shock and arc flash. Before opening any junction box or switch plate: 1. De-energize the circuit at the main consumer unit/breaker panel (turn off the 6A lighting MCB or 15A AFCI breaker). 2. Lock the panel or place a warning tag to prevent accidental re-energization. 3. Verify dead using a proven CAT III or CAT IV two-pole voltage indicator or non-contact voltage tester (NCVT) on a known live source, then on the target wires, then back on the known live source. Never rely solely on a switch toggle or a single-pole tester.
Understanding 2-Way vs 3-Way Terminology
The terminology difference between regions causes massive confusion on the workbench. A UK/AU "2-way" switch has three terminals (COM, L1, L2). A US "3-way" switch also has three functional terminals (Common, Traveler 1, Traveler 2). Do not confuse a UK 2-way switch with a US single-pole switch (which only has two terminals and is sometimes colloquially misnamed a 2-way). For this installation guide, we will walk through the standard UK/AU Loop-in at Switch 1 topology using 1.5mm² Twin & Earth (T&E) and 3-core strapper cable. US/Canadian readers using 14/3 NM-B cable should refer to the Master Table below for exact terminal and color translations.
Tools, Materials, and Cable Specifications
Using the correct cable gauge and switch rating prevents overheating and voltage drop. Lighting circuits are typically protected by a 6A MCB (UK/AU) or a 15A AFCI breaker (US).
- Switches: 2x 10A or 16A rated 2-way switches (e.g., MK Logic Plus, Crabtree, or Schneider Electric for UK/AU; Leviton Decora or Lutron for US 3-way).
- Feed & Load Cable (UK/AU): 1.5mm² Twin & Earth (T&E) — rated for 16A clipped direct, perfectly safe for a 6A protected lighting radial.
- Strapper Cable (UK/AU): 1.5mm² 3-core and Earth (Brown, Black, Grey, plus bare CPC).
- US Equivalent Cable: 14/2 NM-B for line/load feeds, 14/3 NM-B for travelers (Red, Black, White, Bare).
- Connectors: Wago 221 lever nuts (rated 32A, 450V) for neutral and earth splices; avoid twist-on wire nuts in UK/AU jurisdictions.
- Sleeving: Green/Yellow earth sleeving (for bare CPCs) and Brown sleeving (to identify switched lives on strapper cores).
- Test Equipment: CAT III/IV Two-pole voltage indicator, digital multimeter (DMM) with continuity beep.
Terminal and Wire Color Mapping (The Master Table)
This table is your cheat sheet. It maps the exact function to the terminal name and the required wire color for both UK/AU harmonised standards (BS 7671 / AS/NZS 3000) and US NEC standards. Note: In the UK/AU, any core used as a switched live or strapper that is not naturally brown must be sleeved brown at the termination to indicate it carries live voltage.
| Circuit Function | UK/AU Terminal | UK/AU Wire Color (Harmonised) | US Terminal | US Wire Color (NM-B) |
|---|---|---|---|---|
| Permanent Live In (Feed) | Switch 1 COM | Brown (from T&E) | Switch 1 Common (Dark Screw) | Black (from 14/2) |
| Strapper / Traveler 1 | L1 (Both Switches) | Black (sleeved Brown) | Brass Screw 1 | Red (from 14/3) |
| Strapper / Traveler 2 | L2 (Both Switches) | Grey (sleeved Brown) | Brass Screw 2 | Black (from 14/3) |
| Switched Live Out (to Load) | Switch 2 COM | Brown (from 3-core) | Switch 2 Common (Dark Screw) | Black (from 14/3) |
| Neutral Return | Not at switch (Wago splice) | Blue (from T&E) | Not at switch (Wire nut splice) | White (from 14/2) |
| Protective Earth / Ground | Earth Terminal | Green/Yellow (or bare sleeved) | Green Screw | Bare Copper |
Step-by-Step Wiring Procedure (UK/AU Loop-In Method)
The following steps assume a standard radial lighting circuit where the permanent feed enters Switch 1, a 3-core strapper runs between Switch 1 and Switch 2, and the switched live continues from Switch 2 to the ceiling light fixture. The neutral is looped directly to the light fitting via the ceiling rose or a junction box.
Step 1: Prepare the Cables and Earths
Strip 15mm of insulation from all cable ends. Immediately slide Green/Yellow sleeving over all bare Copper Protective Conductors (CPCs). Connect all earth wires together in the backbox using a Wago 221 lever nut or the switch's dedicated earth terminal block. Never leave a bare earth wire floating in the backbox.
Step 2: Terminate Switch 1 (The Feed Switch)
Switch 1 receives the permanent live feed and sends the two strappers to Switch 2.
- Connect the Brown wire from the incoming Feed T&E directly to the COM terminal on Switch 1.
- Take the Black wire from the 3-core strapper cable, slide a piece of Brown sleeving over the end, and terminate it in the L1 terminal.
- Take the Grey wire from the 3-core strapper cable, slide Brown sleeving over the end, and terminate it in the L2 terminal.
- The Brown wire in the 3-core strapper cable is not used at Switch 1 in this specific topology. Cap it safely with a Wago connector and tuck it into the backbox.
Step 3: Terminate Switch 2 (The Load Switch)
Switch 2 receives the strappers and outputs the switched live to the light fixture.
- Connect the Black strapper wire (with brown sleeving) to the L1 terminal on Switch 2.
- Connect the Grey strapper wire (with brown sleeving) to the L2 terminal on Switch 2.
- Connect the Brown wire from the 3-core strapper cable to the COM terminal on Switch 2. This wire now acts as your Switched Live.
- Run this Switched Live (Brown) from Switch 2's COM terminal up to the Live terminal on your light fixture.
Step 4: Terminate the Light Fixture
At the ceiling fitting, connect the Switched Live (Brown from Switch 2 COM) to the fixture's Live (L) terminal. Connect the permanent Neutral (Blue from the main feed, routed via the ceiling) to the fixture's Neutral (N) terminal. Connect the Green/Yellow earth to the fixture's earth point or metal chassis.
Verification and Testing Protocol
Do not energize the circuit until you have completed these bench tests. Set your digital multimeter to the continuity setting (the diode symbol that beeps).
- Short Circuit Check: Place one probe on the COM terminal of Switch 1 and the other on the Neutral splice. The meter must read OL (Open Loop) or infinite resistance. If it beeps or reads < 1 ohm, you have a dead short—re-check your terminations.
- Strapper Continuity: With the power still OFF, place one probe on L1 of Switch 1 and the other on L1 of Switch 2. Toggle the switches. You should read < 1 ohm in at least one toggle configuration, and OL in the other. Repeat for L2 to L2.
- Energize and Voltage Test: Turn the MCB/breaker back on. Set your multimeter to AC Voltage (V~). At the light fixture, measure between the Live and Neutral terminals. You should read 230V AC (±10%) in the UK/AU (or 120V AC in the US) when the switches are toggled to the "ON" state, and 0V when toggled "OFF".
The Most Common Botch (And How to Fix It)
The Symptom: The light turns on and off from Switch 1, but Switch 2 only works if Switch 1 is left in one specific position. If you flip Switch 1 the other way, Switch 2 becomes completely dead.
The Cause: You have swapped the COM terminal with an L1/L2 terminal on one of the switches. Specifically, the permanent live feed was landed on L1 instead of COM at Switch 1, or the switched live to the fixture was landed on L1 instead of COM at Switch 2. When the COM terminal is miswired, the internal mechanical linkage of the switch cannot bridge the gap correctly between the feed and the travelers. The circuit only completes when the miswired switch happens to route the live feed to the specific traveler that is currently connected to the COM of the second switch.
The Fix: De-energize the circuit. Identify the permanent live feed wire (using your NCVT or by tracing back to the panel). Ensure this wire is only connected to the COM terminal on Switch 1. Ensure the wire running up to the light fixture is only connected to the COM terminal on Switch 2. The L1 and L2 terminals are strictly for the interconnecting strappers/travelers and are interchangeable with each other (swapping L1 and L2 simply reverses the physical toggle direction of the switches, which is harmless).
For further reading on regional compliance, refer to the Electrical Safety First guidelines for UK domestic wiring, or consult NFPA 70 (NEC) Article 404 for US switch installation requirements. Always defer to your local Authority Having Jurisdiction (AHJ) for final code compliance.
