Porraskytkentä

Porraskytkentä, also known as staircase wiring or hotel wiring, is an electrical wiring configuration used to control a single light or group of lights from multiple locations, typically two or more. This system is commonly found in stairwells, long hallways, or any area where access points are numerous.

The core of porraskytkentä relies on a specific type of switch called a "vaihtokytkin" in Finnish, or a changeover switch in English. Each switch has three terminals: a common terminal and two switching terminals. When a light is controlled by two switches, the wiring connects the live wire to the common terminal of the first switch. The two switching terminals of the first switch are then connected to the two switching terminals of the second switch using two "looping" or "traveller" wires. Finally, the common terminal of the second switch is connected to the light fixture.

By toggling either switch, the current path is redirected through one of the looping wires, either completing or breaking the circuit to the light. This allows the user to turn the light on or off from any of the switch locations independently of the other switches. For controlling a light from more than two locations, intermediate switches, known as "ristikytkin" (cross switch), are inserted between the two end changeover switches. A cross switch has four terminals and reverses the connections of the looping wires, allowing for more complex control configurations.