Two-way switch (conmutador, three-way switch in the US)

What a two-way switch is

From the outside it looks like an ordinary switch, but inside it has three terminals instead of two. A one-way switch opens or closes the circuit; a two-way switch sends the current down one of two paths. With two of them linked, either can turn the light on if it is off, or off if it is on. In the US the same device is called a three-way switch.

How it is wired

• The live wire reaches the common terminal of the first switch.
• Two wires, called strappers, run between the two switches.
• From the common terminal of the second switch, a wire goes to the light.

For three or more points, intermediate switches (cruzamientos; four-way switches in the US) go between the two, one per extra point. Each needs four wires, so the wiring gets complicated quickly.

Two-way switch or latching relay

With many switching points, a latching relay (telerruptor) is often better: the push buttons are wired in parallel, you can add as many as you like and the wiring is simpler. For hallways and stairs used occasionally, a presence detector is another option.

Where it is used

• Hallways with two entrances.
• Bedrooms, with one point at the door and another by the bed.
• Stairs in duplexes and houses.
• Living rooms with two doors.

What adding one costs

If the conduits have room, swapping a switch for a two-way one and adding the second point is a simple job: a switch costs 30 to 50 euros as a guide. If walls must be chased for new cables, a new line with chasing is roughly 80 to 150 euros. Prices plus VAT. See extra sockets and lights and small electrical jobs in Seville, Spain.