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Electrical switches are devices that can make, break or divert an electrical current. These may be mechanical, electrical or electronic, and are composed of two or more contacts, mounted on an insulated structure, that can be moved in and out of contact with each other. As the use of electric and electronic items has expanded, a wide range of switches have been developed in numerous styles, including many varieties of toggle, keyboard, dial, push button and rocker configurations.
These switches fall into two basic categories: power switches and signal switches. Power switches are used to energize or de-energize an electric load and are commonly found on light switches, power tools and appliances. Load-break switches are used in high voltage power systems that require arc interrupters, or safety devices that detect electrical arc and interrupt the current, similar to the function of a circuit breaker.
Signal electrical switches are set to react to circumstances that require a preset response, and are found in devices like the thermostat on a heater or air conditioner. When a certain temperature is reached, the thermostat will turn another switch on or off. Signal switches are also found in freezers, refrigerators, and sensor-triggered security lights. Some security lights are activated by photoelectric light controls that are triggered when the natural light has dimmed or brightened to a certain level.
The most common are mechanical switches, which make or break an electrical contact when some force, either manual or magnetic, is applied to move the switch to an on or off position. Toggle switches have a lever that is pushed or pulled, like the common light switch. Power windows and locks in automobiles use rocker switches, which rock back and forth when pressed. Keyboard switches are found on computers, washers, stoves and other devices with push controls.
Electronic switches do not have mechanical contacts, but use semiconductor devices instead. These switches apply electrical control signals to terminals on the switch that opens and closes the contacts. Touch plate devices, soft-touch controls and motion detector switches are frequently electronic. Some electronic safety switches mounted on food processing equipment use radio frequencies that will interrupt the power when a safety door is opened. Electronic switches are available in a vast range of configurations such as toggle, rocker, push button, rotary, slide, and reed and relay switches.
Electronic electrical switches have medical applications as well. Electric stimulation devices are used to rehabilitate and accelerate healing in damaged tissues. Transcutaneous electrical nerve stimulation devices (TENS), neuromuscular electrical stimulation devices (NMES) and functional neuromuscular stimulation devices (FNS or ENS) use current, controlled by switches, to relieve pain, relax muscles, increase blood circulation and prevent muscle atrophy.