Installing a Dimmer Switch: A Step by Step Guide

Installing a dimmer switch to your lights is one of the easier electrical projects one can tackle around the house, and can add a touch of class to the lighting of any room. What follows is a brief, step by step guide to doing so easily, efficiently and safely. Dimmer switches come in two main varieties: Those that look like a conventional light switch (examples), or those with rotary knobs (examples). Choosing between either is simply an aesthetic choice, as both do the same job; choose whichever you feel will look best on your wall. Dimmers are also a useful way nowadays of conserving energy. Most dimmers these days use silicon controlled rectifiers rather than resistors to control the AC waveform nowadays, which can lead to a saving in electricity used. Check with your retailer when buying to see which type you are buying, and you could also end up saving the Earth a little!

Few tools are needed for the procedure: A screwdriver, a pair of wire strippers, a pair of needle-nose pliers, insulating tape, wire nuts, and perhaps a voltage tester, which are fairly cheap nowadays and can be picked up at most hardware stores (example), and can come in handy for many household DIY projects.

Safety is paramount when dealing with any electrical installations around the house, as you’re no doubt already aware, but I can’t stress the importance of this enough. Before beginning the procedure, make sure you have turned off the power to the circuit involved, at the main junction box or circuit breaker for your home. It may sound obvious, but it’s surprising how many accidents are caused each year by neglecting this simple step.

Once you are sure the power is off, remove the screws holding the switchplate to the wall with an ordinary screwdriver. Pull back, and unscrew the switch itself. Remove carefully; wiring behind walls can over the years become quite fragile and brittle, and liable to break off if handled roughly. The voltage tester can be used at this point to confirm the electricity to the circuit is off. Unscrew (again, carefully) the wiring from the switch itself. Discard the old switch unless you’re sure of it’s provenance and age; reusing such devices elsewhere can cause problems if you’re not sure how reliable it is.

Using the wire strippers, make sure around 2-3/8″ of wire is exposed at the end of end piece of wiring. Nowadays, most new dimmer switches will come with pre-wired, pre-stripped wires attached; attach these carefully as per the instructions included with the dimmer, preferably using wire nuts to hold in place. Once attached, use around 2-3″ of insulating tape to cover any exposed wire, and prevent the risk of electrical shorts. Replace gently, and screw the switch and switchplate into place. Make sure your dimmer is turned to the off position, and then restore electricity to the circuit. Slowly turn the switch to test.

And that’s it! You’ve installed your first dimmer switch.