Light Switch Types and the Importance of Switching the Right Wire

This is pretty basic for those who are more familiar with electrical wiring, but many beginners may not know this. Connecting the proper wire to a light switch, or any switch for that matter, is extremely important. Generally speaking, you will be working with two wires – one hot, and one neutral. The individual colors will vary depending on where you live – see my article Color Code for Electrical Wiring.

In order to understand why this is so important, you must first understand what it is that a switch does – and I don’t just mean “it turns something on or off”. As you toggle a switch on and off, you’re essentially forming a circuit and then severing light switch with wiring visiblethe circuit. By turning the switch off, it’s like closing the water gate in a dam, thereby preventing water from flowing through.

The problem arises when you run the neutral through the switch instead of the hot, as this will be like having a permanently opened water gate that you have no control over where the water is flowing through continuously. Switching off the neutral doesn’t change the fact that the power is still getting to the fixture. (In this article, I’ll be talking mainly about light switches.)

  • Rule of Thumb: When connecting 2-way switches, always run the hot through the switch! This ensures that the light fixture won’t be live when the switch is off. Doing this the other way around is dangerous as most people assume a fixture is dead when it’s switched off.

The 2-way Switch

Let’s start out with the most common – the 2-way switch (1-way in the UK). A 2-way switch is the kind that only allows you to turn an appliance – eg. a light – on or off from one location. This is sufficient for most situations and is therefore the most common. Electrically, this kind of switch is known as a single pole single throw (SPST, see image below), and is simply connected by inserting the hot wire in and extending it out to your appliance – the neutral is unswitched and continues on directly.

spst switch illustration

The 3-way Switch – Traveler System vs. California 3-way

Now the 3-way switch (2-way in the UK) is the kind of switch that allows you to control a light fixture or similar appliance from two separate locations – from either end of a hall for example. Although not used as frequently as the 2-way this is still a very convenient switch to know about. Referred to electrically as a single pole double throw (SPDT, see image below), this switch is best connected with 3 wire as you’ll need exactly 3 wires going between the switches including the neutral.

spdt switch illustration

Although there is an alternative connection method called the California 3-way, it uses 3 wires between the switches instead of 2, and 4 if you count the neutral. This method has an advantage in that it allows you to add a second light at A (see the diagram), which will be electrically parallel to the first light. You can also add an outlet at B as B is always live.

3-way Alternative system

However, this method is not the easiest or most used, and can be confusing for those who aren’t familiar with this form of connection. The simplest and therefore most common form of 3-way connection is what’s called the “traveler system” – see images below. This system simply feeds the hot line into the common terminal of one of the 3-way switches.

A pair of “travelers” is then connected to the two “uncommon” terminals, connecting both 3-way switches. The light fixture is then connected to the common terminal of the second switch. The neutral wire is simply extended as necessary and should bypass the switch completely. And there you have your 3-way switch, all ready and waiting to make life easier for you! The diagram below shows the 2 possible on-off combinations with the 3-way traveler system.

3-way switch on-off illustration

The 4-way Switch

Now the last one we’ll be talking about in this article is the 4-way system (3-way or intermediate switch in the UK, see image below). This is the one you’d need if you wanted to control a given light from 3 or more locations. That’s right, 4-way switch diagram3 or more. Theoretically, you can switch a light on or off from an infinite number of locations using the following method. It’s simply using 4-way switches sandwiched between 2 3-way switches.

  • Often, there won’t be any visible difference between a 3-way and a 4-way switch except a diagram on the backside. So it’s important to examine the diagram and make sure you have the right switch for the right place.

The connection of a 4-way switch system is very similar to a 3-way system. You connect your hot line to the common terminal of your 3-way and extend your travelers to the 4-way. You then continue extending travelers to 4-ways as needed, ending with your 3-way, which then connects to your light fixture. The diagram below shows all 4 possible on-off combinations and should clarify any confusion.

4-way switch on-off illustration

4-way switch on-off illustration

By increasing the number of 4-way switches between the 3-way switches, you can increase the number of locations from which to control the light. Some examples of places that might need a 4-way switch are particularly long hallways with several branch-offs as well as rooms and large rooms with several exits and entrances. Just don’t overdo, as the more switches you add the more wiring you’ll need!

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