Installing a two-way switch: the wiring explained
A two-way switch lets you turn the same lighting point on and off from two different switches, an indispensable comfort at the top and bottom of a staircase or at both ends of a hallway. The principle relies on three wires connecting the two switches. This guide explains the necessary gear, the complete wiring and the safety rules to follow.
Understanding the principle of the two-way switch
A standard switch has two terminals (a live in and a lamp return). A two-way switch has three: the common terminal (L or P) and two traveller terminals (1 and 2). The two switches are connected by two wires called travellers. The lamp turns on when the live reaches it, which depends on the position of the two switches.
The necessary gear
- Two two-way switches bearing the CE and NF markings
- Three wires: one live wire (red or brown), two traveller wires (black or orange) and one lamp return wire
- Conduits and recessed boxes suited to the thickness of your partition
- An insulated screwdriver, a wire stripper and a pair of cutters
- A voltage tester to check there is no power
- Wago connectors or connection terminals for the connections at the ceiling
The wiring between the two switches
- Run three wires between the two boxes: two travellers and one lamp return wire.
- At the first switch, connect the live to the common terminal (L or P).
- Connect the two travellers to terminals 1 and 2 of each switch, in the same order on both sides.
- At the second switch, connect the lamp return wire to its common terminal.
- At the ceiling, connect the live of the second circuit and the lamp return to the lighting point.
The order of the travellers does not matter for operation, but it is wise to keep the same colour code on both sides for future work. All the connections are made inside the boxes, in suitable terminals. The wires must be stripped to about 10 millimetres and firmly tightened to avoid any overheating.
Connecting to the consumer unit and the lamp
At the consumer unit, each lighting circuit is protected by a 10 or 16 amp MCB and can be connected to a 30 mA RCD. Connect the circuit live to the corresponding terminal of the MCB, then connect the conductors to the terminal blocks. The neutral and earth are connected to the bars provided for this purpose.
Testing the operation
- Refit the mechanisms in the boxes and the finishing plates.
- Restore the power at the consumer unit, then test the lamp from the first switch.
- Turn it off from the second switch, then on again from the first to check the toggling.
- Repeat the operation several times: the two-way switch must work in both directions.
- If the lamp does not light up, switch off the power and check the connections one by one.
The mistakes to avoid
- Confusing the common and traveller terminals, which prevents turning off from one of the switches
- Working without checking the absence of voltage with a tester
- Using wires of insufficient cross-section (1.5 mm² is the minimum for lighting)
- Connecting the earth to a traveller terminal, a guaranteed short circuit
Once the two-way switch is installed and tested, you have a light controlled from two places, with no visible wiring and in accordance with current standards. If your configuration requires three control points, you will need to add a so-called intermediate switch in the middle of the circuit. Take the time to check each connection and do not hesitate to ask an electrician for advice on complex configurations.