2-Way Switching

2-way switching lets you control one light from two different locations — for example at the top and bottom of a staircase, or both ends of a long hallway. With a modern 3-plate loop-in ceiling rose, the lamp stays connected to the rose and the two switches sit on a loop that returns to the rose. The travellers between the two switches run in a single 3-core+E cable.

How a 2-Way Switch Works

A 2-way switch has three terminals:

• COM — the common pole. Connected internally to either L1 or L2 depending on the lever position.
• L1 — one of the two switched outputs.
• L2 — the other switched output.

In a 2-way pair, the two switches' L1/L2 terminals are joined to each other by the strapping cable. Perm live enters at one switch's COM and switched live leaves at the other switch's COM. Toggling either lever changes which traveller (L1 or L2) is in the circuit, so flipping either switch reverses the lamp's state.

Inside the Switch

A 2-way switch is a single-pole double-throw (SPDT) device. A spring-loaded contact arm pivots at the COM terminal and lands on either L1 or L2 — never both, never neither. Flipping the lever flicks the arm from one side to the other.

When two such switches are wired in series with their L1↔L1 and L2↔L2 travellers, the lamp is on whenever the two arms match (both pointing to L1 or both pointing to L2). If the arms disagree the path is broken — so flipping either switch toggles the lamp.

Wiring Diagram

In the diagram above, both switch arms point to L1, so the L1 traveller carries current all the way through. Flicking either switch to L2 — but not both — breaks the L1 path without making the L2 path, and the lamp goes off.

Following the Current

1. Perm live leaves the consumer unit and enters the rose's loop terminal.
2. From the rose's switch terminal a 3-core+E cable drops down to SW1. The brown conductor carries perm L into SW1.COM.
3. SW1 routes that live to either L1 or L2 depending on the lever position.
4. The chosen traveller crosses to SW2 via the strapping cable and lands on SW2.L1 or SW2.L2.
5. SW2 then routes whichever traveller is selected through to SW2.COM.
6. SW2.COM is the switched-live return. It travels back through the third core of the strapping cable to SW1, and up the grey conductor of the rose drop to the rose's switch terminal.
7. The rose's switch terminal is wired internally to the lamp's brown core via the pendant flex, so the lamp lights up.

Flipping either lever swaps which traveller carries the current, breaking the path through the lamp.

Cables Required

Sleeving Rule

Any blue or grey conductor that carries live at any point — including the switched return and both travellers — must be sleeved brown at both ends. In practice that means almost every core in the rose drop and strapping cables gets brown sleeve.