Wiring a dimmer switch

LAST UPDATED: 15th January 2023 by The Editorial Team

Man wiring a dimmer switch

Summary: Step by step guide and video showing how to install and wire a dimmer switch.

How to fit a dimmer switch

Dimmer switches provide a relatively inexpensive and uncomplicated way to vary the intensity of light in a room. There are three types of ‘dimmer’ for light fittings: touch dimmers, switch dimmers and remote dimmers. Although these types of dimmer switches can be fitted to low voltage halogen lights, they are not suitable for use with fluorescent lights.

Types of dimmer

  • Touch dimmers work by induction. Simply by touching a lamp base or light switch, you can dim the light in stages.
  • Switch dimmers are fixed to a floor or table lamp and worked by hand or foot. Rotating switches are used on wall switch plates.
  • Remote dimmers have a touch sensitive switch controlled by a remote control, which can be programmed to remember light settings.

Installing a dimmer switch

  • Cut off the power supply to the relevant circuit from the consumer unit.
  • Unscrew the switch plate, and pull it gently away from the wall.
  • Before disconnecting the colour-coded cores make a note of which terminals they connect to, so you know where to reconnect them on the new switch plate.
  • Unscrew the screws fixing the mounting box to the wall to remove the mounting box.
  • The dimmer switch will need to be flush-mounted. Follow instructions for installing a mounting box for guidance on creating a recess for the mounting box.
  • Mark the position of the pilot holes for the screws for the new mounting box.
  • Use a cable detector to ensure there are no cables in the way before you drill and plug the new holes.
  • Feed the cable through the hole in the mounting box and screw the mounting box to the wall.
  • If you have a metal face-plate on the switch, install a PVC guard between the wall and face-plate.
  • Reconnect the cores. Most dimmer-switches will be two-way (have 3 terminals). To replace a single one-way light switch, only use the terminals marked Com and L1. If the switch is two-way you will use all three terminals.
  • If you have a metal mounting box, be sure the earth core is connected to earth terminals in both the switch and the mounting box. With plastic mounting boxes, the earth cable should be placed in a plastic strip connector.
  • Replace the switch plate and screw it into place.

Tools needed

  • Insulated screwdriver
  • Padsaw (For plasterboard)
  • Bolster (For masonry)
  • Lump hammer (For masonry)
  • Cable detector
  • Power drill

Materials needed

  • Dimmer switch
  • Wall plugs
  • Plastic strip connector (For plastic mounting boxes)
  • PVC guard (For metal faceplate)

Important note

The colour-coding system for electric cable changed in 2006, make sure you read Electric cable and flex to view the new information.

How to wire a dimmer switch video

Author

The Editorial Team

The Editorial Team at lets-do-diy.com are a team of experts led by Mark Wilson. We have been creating DIY projects, articles, costs guides and product reviews since 2008. For more info see our about page.