Two-Way Switching Explained: COM, L1, L2 & Intermediates

Two-way switching lets two switches control one light — hall and landing, either end of a corridor, or both sides of a hotel bed. Here's how it works, what the terminals mean, and how three or more switch positions are handled.

How two-way switching works

Each 2-way switch has three terminals: COM (common), L1 and L2. The two switches are linked by a pair of strapper conductors between their L1 and L2 terminals. Flipping either switch swaps which strapper is live, toggling the light regardless of the other switch's position.

Wiring diagram: two-way circuit (UK colours)

ConsumerunitSwitch 1COML1L2Switch 2L1L2COMPermanent liveL1 strapper — black*L2 strapper — grey*To light* Run 3-core & earth between switches; sleeve black and grey cores brown — they are live conductors.
Schematic only. Neutral runs directly to the light fitting; earth to every back box and metal plate.
  • Switch A: permanent live into COM; L1/L2 out as strappers.
  • Switch B: strappers into L1/L2; switched live from COM to the light.

Older installations may use the "conversion" method with the loop at the ceiling rose — the terminal logic at the switches is the same.

Three or more switches: the intermediate switch

For a light controlled from three positions (top, middle and bottom of a staircase), the middle switch is an intermediate switch. It sits in the strappers between the two 2-way switches and cross-connects them each time it's flipped. You can chain any number of intermediates.

Buying the right switch

  • All Kent Traders BG light switches are 2-way as standard — a 2-way switch works perfectly in a 1-way circuit, so you never need to stock both.
  • Dimming a two-way circuit? Standard practice is one dimmer plus one 2-way plate switch; check our dimmer guide for LED-friendly 2-way dimming options in dimmer switches.
  • Hotels and HMOs: corridor and stairwell switching is a common EICR observation when altered badly — our EICR checklist covers what inspectors look for.
Safety: Re-wiring switching arrangements goes beyond like-for-like replacement. Isolate at the consumer unit, prove dead, and if you're adding new cable runs or converting 1-way to 2-way, have the work done or verified by a qualified electrician to BS 7671.

FAQs

What's the difference between 1-way and 2-way switches?

A 1-way switch is a simple on/off with two terminals. A 2-way switch has three (COM, L1, L2) so a pair can control one light from two places. 2-way switches can always be used as 1-way.

Can I convert 1-way to 2-way switching?

Yes — it needs a 3-core & earth cable run between the two switch positions and correct terminal connections at both ends. This is new wiring, so most people use an electrician.

What cable links two-way switches?

3-core & earth (brown, black, grey) is standard for the strappers and common feed between switches, with cores sleeved brown where used as live.