How Does a Light Switch Work?

The light switch—it’s something we take for granted dozens, if not hundreds, of times every day. But if improperly wired, a switch can be an accident waiting to happen.

What Does a Light Switch Do?

An electrical circuit is just what the name implies—a more-or-less circular path through which electricity flows. If there’s a light in the circuit, the bulb draws the current through itself to cause it to glow before the electricity continues on its “circuitous” journey. Break that circuit, and the electricity stops flowing and the bulb doesn’t light up. Sounds simple enough. And that’s the function of a light switch.

What’s Hot and What’s Not

Electrical wiring circuits typically contain three wires. One is the feed wire—the source of the electrical current—and one is the neutral or return wire—the wire that carries the current back to the source, completing the circuit. The third wire is a ground wire to discharge any stray current safely. In electrical parlance, the feed wire is known as the “hot” wire and the neutral wire is usually referred to as either that or as the “return.”

The wires are marked with colored insulation to identify them. The hot wire will be usually be black. The neutral is normally white, but can be any color other than green (including black, unfortunately), and the ground, if there is one, will be either green or bare wire. If for some reason a white or colored wire is being used as the hot wire, it should have a piece of black tape attached to it.

A single-pole light switch has two or three terminals to attach the wires, one on one side with a brass screw for the hot wire, one on the other side with a silver screw for the neutral, and possibly one with a green screw for the ground wire. Some may also have push-in holes on the back, but those are more likely to work loose and cause problems. Use the screw terminals for a proper installation.

Why It Matters

Logic tells us that by breaking the flow of current at any point in the circuit will stop electricity from flowing, causing the light to turn off, and a switch is the easiest way to accomplish that. And that’s true. But what logic doesn’t tell us is that it’s important how that switch is wired.
A switch is designed to break the circuit on its hot side. That’s important because it prevents current from ever reaching the light or other device on the circuit. If the switch is wired “backwards,” with the hot wire attached to the silver neutral screw, in other words, the circuit is broken, but the socket remains energized, creating a shock hazard if you or any other conductor touch it while grounded. Connect the switch properly and the current will never reach the socket when the switch is the “off” position.

When to Call a Pro

There are other considerations when adding or replacing switches such as three-way switches or dimmers. Those will be addressed in future articles. Meanwhile, if you’re uncomfortable or uncertain about wiring a switch, be safe and call a pro. Working on wiring, switches, and outlets safely requires knowledge of electrical circuitry and codes, so don’t risk injury, shock, fire hazards, or expensive repairs by getting in over your head.

If you have any problems or concerns about your electrical service, the pros at Allstar Electrical Services are ready to solve them for you. We offer homeowners, builders, and businesses reliable, professional electrical work that is safe and up to code. Reach us at (303) 399-7420!