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A time switch (also called a timer switch, or simply a timer) is a timer that operates an electric switch controlled by the timing mechanism.

The switch may be connected to an electric circuit operating from mains power, including via a relay or contactor; or low voltage, including battery-operated equipment in vehicles. It may be built into power circuits (as with central heating or water heater timer), plugged into a wall outlet with equipment plugged into the timer instead of directly into the PowerPoint; or built into the equipment.

The mechanism may be mechanical (e.g., clockwork; rarely used nowadays), electromechanical (e.g., a slowly rotating geared motor that mechanically operates switches), or electronic, with semiconductor timing circuitry and switching devices and no moving parts.

The timer may switch equipment on, off, or both, at a preset time or times, after a preset interval, or cyclically. A countdown time switch switches power, usually off, after a preset time. A cyclical timer switches equipment both on and off at preset times over a period, then repeats the cycle; the period is usually 24 hours or 7 days.

Timers may do other processing or have sensors; for example, a timer may switch on lights only during hours of darkness, using a seasonal algorithm[2] or light sensor. Combining the two allows light to come on at sundown and go off at midnight, for example.

Digital time switches

With ABB's digital timer switches, you can cut your energy consumption easily. The DBT timer app allows you to perfectly program the energy usage with a significantly reduced configuration time.