By John Papiewski | Updated Mar 24, 2022
Electrical circuits require a complete path for current to flow. A switch breaks that path until you need it. The push‑button switch—found in elevators, car stereos, and countless other devices—comes in two primary variants: momentary and non‑momentary.
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Construction
A push‑button switch is a compact, sealed assembly that completes an electrical circuit when depressed. Inside, a metal spring engages two conductive terminals, allowing current to flow. When released, the spring retracts, breaking the connection. The housing is typically non‑conductive plastic to protect users from electric shock.
Momentary Switches
Momentary switches conduct only while they are pressed. They are commonly used for devices that require a short, intentional signal, such as telephone keypads, calculators, and doorbell buttons.
Normally‑Off
In a normally‑off configuration, the circuit remains open until the button is pressed. This is the most common setup for push‑button switches. Examples include doorbell buttons, cell‑phone keypads, and garage‑door openers.
Normally‑On
Conversely, a normally‑on switch keeps the circuit closed until the button is pressed, at which point it opens. This variant is less common but can be useful in specialized wiring schemes—for instance, wiring a normally‑on switch in parallel with a light bulb so that pressing the button turns the light on while the switch remains off.
Non‑Momentary Switches
Non‑momentary switches toggle their state with each press, acting as a simple on/off switch. Power buttons on TVs, stereos, and many other consumer electronics use this type of switch.
Electrical Ratings
To ensure reliability and safety, switches are rated for the maximum current and voltage they can handle. Higher voltage or current demands necessitate larger, more expensive components. For example, a mobile phone’s power supply may only need a few milliamps, whereas industrial machinery might require a switch rated for hundreds of amps.
Understanding the construction, operation, and rating of push‑button switches helps engineers and hobbyists select the right component for their circuits.
