What Does Common Mean in Wiring: A Comprehensive Guide

what does common mean in wiring

What Does Common Mean in Wiring: A Comprehensive Guide

Wiring is an essential aspect of electrical systems, and understanding its terminology is crucial for anyone involved in electrical work. One term that often comes up is “common.” In this comprehensive guide, we will explore what “common” means in wiring and how it is used in electrical circuits.

Understanding Common in Electrical Circuits

In electrical circuits, the term “common” refers to a connection point or terminal that is shared by multiple components or devices. It is also known as the “common terminal” or “common connection.” The common terminal acts as a reference point for the circuit and is typically connected to the ground or the negative terminal of a power source.

Common in Switches

One common application of the term “common” is in switches. Switches are devices used to control the flow of electricity in a circuit. They have three terminals: the common terminal, the normally open (NO) terminal, and the normally closed (NC) terminal.

The common terminal in a switch is the point where the current flows when the switch is in the “on” position. When the switch is flipped to the “off” position, the common terminal disconnects from the NO terminal and connects to the NC terminal, interrupting the flow of electricity.

Common in Relays

Relays are electromagnetic switches used to control high-power circuits with low-power signals. They also have a common terminal, along with a normally open and normally closed terminal. The common terminal in a relay serves a similar purpose as in switches, providing a reference point for the circuit.

When the relay is energized, the common terminal connects to the normally open terminal, allowing the current to flow. Conversely, when the relay is not energized, the common terminal connects to the normally closed terminal, interrupting the current flow.

Common in Grounding

In electrical systems, grounding is crucial for safety and proper functioning. The common terminal is often connected to the ground, which provides a path for excess electrical current to flow safely into the earth. This helps prevent electrical shocks and protects equipment from damage caused by voltage surges.


Understanding the term “common” in wiring is essential for anyone working with electrical circuits. Whether it’s in switches, relays, or grounding, the common terminal serves as a reference point and plays a crucial role in controlling the flow of electricity. By grasping the concept of “common,” you can ensure the safe and efficient operation of electrical systems.

Remember to always consult a professional electrician or refer to the manufacturer’s guidelines for specific wiring instructions.



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