Three Way Switching 101

Fix-It-Yourself

Prior to 2018 there was no definitive codified standard for how to wire a Three Way Switch. In 2018 The Canadian Electrical code was amended and there is now a rule which requires every switch box to be provided with a neutral conductor. (Traditionally the white wire). This most certainly radically changes a lot of the shenanigans that have been tolerated in residential wiring in past years, and imposes a standard wiring method for switching.

However prior to this rule it was most certainly possible to use a white wire as what is known as a “traveler”. This “traveler” has no direct return to the neutral bus bar in the electrical panel of your home. This is usually where even the smallest home owner DIY jobs can go horribly awry, as this can create a situation where voltage can become present on the white wire!

In order to truly be confident around a three way switch you need to understand what it’s designed to do and how it accomplishes it. A normal switch is very simple. Electrical current arrives to a given point where it is halted. This is known as a terminal. A mechanism must be manually activated in order for current to continue on it’s way. Thus, It is either “on or off”, “yes or no”. Picture a car arriving at a river crossing and a draw bridge must come down in order for the car to continue on it’s way.

A three way switch is different. Electrical current arrives at a given point but unlike a regular switch, it does not have a singular exit point. It has two. The point where current arrives is always the same. This is known as the common terminal on the switch. So returning to the example of the car, river, and bridge. In this case we need to imagine a rail car arriving at a fork on a set of rail tracks. When leaving the fork the rail car can either take the left route or the right route. But never both simultaneously.

And, here is the big mystery of the three way switch system demystified. Imagine both the left track and the right track travelling to the same destination, but upon arrival there is a signal-man waiting by the tracks and only allows traffic from either the left track or the right track to pass forward. After clearing the signal man, the tracks merge back into one possible exit.

Imagine now that this final track leads directly to a lamp, a ceiling fan, or a toaster, and the rail car is carrying electrical current from this one exit. This track or path is what electricians call again: the common terminal. However, this time, it is not connected to a source of electrical current. It is instead connected to an appliance that is destined to receive electrical current. (Also known as a “load”).

Again prior to 2018, electricians could use either red/white or red/black as the traveler (left track or right track) wires. Therefor, it is very important for DIY-ers to know how to identify what they are looking at, and how it functions prior to dismantling the wiring on a three way switch.

Otherwise, you’ll end up needing to call me. Or, one of my electrician brethren.