How to & Guides

How Does 2-Way Switch Wiring Work?

In this article, we will explore the fascinating concept of the 2-Way Switch. Also known as a Staircase Switch, this ingenious device allows you to control a single load, such as a light bulb, from two different locations, just like the ends of a staircase.

Note: Please keep in mind that this article is solely intended to explain the theory behind 2-Way Switch wiring and is not a step-by-step guide for installation or wiring. If you plan on implementing a similar setup in your home, it is highly recommended to consult a professional due to the involvement of 230V AC Supply (or 110V AC, depending on your location).


Switches are a common feature in our everyday lives, whether we’re at home, in the office, or even in our cars. They are an essential component of the gadgets we use regularly, from mobile phones to laptops. In simple terms, a switch is an electrical device that can open or close an electric circuit.

There are various types of switches available, including Toggle Switches, Momentary Switches, Rocker Switches, and Digital Switches, among others. While each switch serves the basic purpose of interrupting or diverting the flow of electric current, there is a unique switch known as the “Two Way Switch” that plays a crucial role in Staircase Lighting.

Before we delve into the wiring of a 2-Way Switch, let’s familiarize ourselves with the Two-Way Light Switch, which is the fundamental component of 2-Way Switching, regardless of the wiring type. This switch is a standard single-pole double-throw switch with three terminals.

The three terminals are typically labeled as COM, L1, and L2. However, you may also come across terminologies like COM, 1 Way, and 2 Way. In one position, the COM and L1 terminals are connected, while in the second position, the COM and L2 terminals are connected.

This connection type is commonly referred to as a “Break before make” design, as the first connection needs to be broken before establishing the second connection. This is in contrast to a regular two-terminal switch, which is simply an on/off device.

See also  AC Breaker Continuously Tripping: Causes and Fixes

Two-Way Light Switch

How to Wire a 2-Way Switch?

As mentioned earlier, a two-way switch is particularly practical for staircase lighting. It allows you to turn on the light just before you start climbing the stairs and turn it off as you reach the top by toggling the switch located there. Let’s explore two different methods for making a two-way switch connection.

Standard 2-Way Switch Wiring

The first wiring method involves using a pair of Two-Way Light Switches with a three-wire control (3 Wire Control). The following schematic illustrates the simple wiring setup for a three-wire 2-Way Switch.

Standard 2-Way Switch 3-Wire Method

In the schematic, you can see that both COM terminals are connected together. The L1 terminals of both switches are connected to the line (or phase or live) of the AC Supply.

The L2 terminals of both switches are connected to one terminal of the light bulb, while the other terminal of the light bulb is connected to the neutral of the AC power supply.

From the schematic, it’s easy to understand how the wiring functions. In the default state depicted in the image, the light is off. Toggling either of the switches will turn the light on. To turn the light off, you can toggle either switch.

For example, in the above state, both COM terminals are connected to their respective L1 terminals. If we toggle Switch 1, connecting COM of Switch 1 to its L2 terminal, a complete circuit path is established, and the light turns on.

To turn off the light, we can toggle either Switch 1 or Switch 2, as any toggling action will break the flow of current to the light. Taking into account all the possibilities, the light will be on under the following two conditions:

  • COM of Switch 1 is connected to L1, and COM of Switch 2 is connected to L2.
  • COM of Switch 1 is connected to L2, and COM of Switch 2 is connected to L1.
See also  Can Airpods Connect to Android?

If we compare this setup to digital electronics, it resembles an Ex-OR Gate, where the light’s status (either ON or OFF) depends on the status of the COM terminals of both switches connected to their respective L1 and L2 terminals.

Here is the truth table for Standard Wiring, also known as 3-Wire Control of a Two-Way Switch, which illustrates how the light’s status depends on the terminal (L1 or L2) connected to the COM terminal.

Switch 1 COM (connected to) Switch 2 COM (connected to) Status of Light
L1 L2 ON
L2 L1 ON

This wiring method is recommended since it involves a lighting circuit (or breaker) where both the line and neutral wires originate, despite its use of additional wires.

Alternative Method of Two-Way Switch Wiring

The next wiring design is an older system that you may come across in some older homes and industrial settings. It is known as two-wire control wiring (2 Wire Control).

It’s important to note that this wiring system is not recommended for modern installations. If you plan on installing a new setup or replacing an older one, it is essential to adhere to the previous wiring method.

We are including the alternative wiring method for reference purposes only, and we will also discuss its drawbacks.

Now, let’s examine the actual wiring setup through the following schematic, which demonstrates the implementation of a two-wire control two-way switch.

Alternative 2-Way Switch 2-Wire Method

In this configuration, the L1 terminals of both switches are connected together, as are the L2 terminals. As for the COM terminals, the COM terminal of the first switch is connected to the phase (or line or live).

The COM terminal of the second switch is connected to one end of the light bulb, while the other end of the light bulb is connected to the neutral of the AC Supply.

In the default state shown in the schematic, the light is off. However, toggling either of the switches will turn the light on. In terms of digital electronics, this configuration is similar to an Ex-NOR Gate.

See also  2 Ohm Vs 4 Ohm Subwoofer: Which Should You Choose?

Here is the truth table for the Alternative Method Wiring, also known as 2-Wire Control of a Two-Way Switch:

Switch 1 COM (connected to) Switch 2 COM (connected to) Status of Light
L1 L1 ON
L2 L2 ON

Although this method saves on cable usage, it is no longer preferred due to the possibility of the phase and neutral wires coming from different lighting circuits (or breakers).

Another significant drawback is related to electromagnetic interference. Any current-carrying conductor emits electromagnetic radiation. When the Live and Neutral wires are in close proximity, they cancel out each other’s EM Radiation.

However, in this particular wiring, the neutral and live wires might be routed separately to different parts of the house, effectively creating a giant induction loop. This can lead to interference problems with other EM and RF signals.


While I don’t have Two-Way Light Switches to physically demonstrate the working, I’ve created a similar setup using a couple of Single Pole Double Throw (SPDT) Toggle Switches and an LED since a two-way switch essentially functions as an SPDT switch.

The SPDT Toggle switch can be considered as a Two-Way Light Switch as it features three terminals and operates similarly to the two-way light switch.

2-Way Switch SPDT

For wiring purposes, I opted for the standard wiring method (the first method, i.e., the 3-wire control) with a 3.7V Lithium-Ion Battery as the power source. The setup worked flawlessly.


This article has provided a comprehensive beginner’s guide to the two-way switch, including its wiring principles, different wiring types for two-way switches, such as Staircase Wiring, and schematics for the wiring configurations.

Remember, when it comes to any electrical installations, it’s always best to consult a professional to ensure safety and compliance with regulations.

To learn more about electronic devices and solutions, visit OnSpec Electronic, Inc..

Related Posts

How to Install a 3-Way Switch: A Comprehensive Guide

How to Install a 3-Way Switch: A Comprehensive Guide

If you need to control an electrical device from multiple locations, such as a staircase light, a 3-way switch wiring is essential. With this wiring setup, you can…

Common Signs of a Faulty Spark Plug

Spark plugs play a critical role in ensuring optimal combustion performance and safeguarding the electrodes from damage. However, spark plugs also require periodic replacement, as worn-out ones can…

Are Beats Studio Buds Waterproof?

The advancements in technology have paved the way for the invention and development of various gadgets and accessories. One such popular and widely used gadget is wireless headphones,…

Quick Guide: Understanding AC Capacitor Wiring Colors

Capacitors are passive electronic components that store electrical energy in an electric field. They consist of two electrically conductive plates insulated with dielectric material. When voltage is applied,…

How to Add New Members to a Group Chat in iMessage?

Messaging applications like WhatsApp and Telegram have gained immense popularity in recent times. The reason for their widespread use is that, in addition to regular text messaging, they…

The Versatile Uses of an Angle Grinder

The Versatile Uses of an Angle Grinder

What is an Angle Grinder Angle Grinders are handheld devices that offer a multitude of functions, including cutting, deburring, polishing, and grinding. It is a highly adaptable tool…