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Electromechanical switches, relays, and contactors “turn power on” when the moving electrode makes contact with the stationary electrode to carry current. Conversely, they “turn power off” when the moving electrode breaks contact and the resulting arc plasma stops burning as the dielectric gap widens sufficiently to prevent current flow.
[1] [2] The term can be applied to a single switch or to an entire device. A simple example of holding current is in a Spark gap. In the most basic of circuits, if the current falls below the holding current even briefly, the circuit is turned 'OFF' (becomes blocked).
Every time an electrical power device (for example: heaters, lamps, motors, transformers or similar power loads) turns on or off, its switch, relay or contactor transitions either from a CLOSED to an OPEN state ("BREAK") or from an OPEN to a CLOSED state ("MAKE"), under load, an electrical arc occurs between the two contact points (electrodes) of the switch.
Unlike machines with an ordinary latching switch (such as a common light switch), when the power is resumed the machine will not operate until being turned on again. As a result, magnetic starters often use momentary switches for "off" and "on" functions, as this type of switch returns to a defined normal position when released. Latching ...
A toggle light switch Internal components of a toggle switch. The toggle mechanism provides "snap-action" through the use of an "over-center" geometry. The design was patented in 1916 by William J. Newton and Morris Goldberg. [2] The switch actuator does not control the contacts directly, but through an intermediate arrangement of springs and ...
People walking along the street observed sparks jumping between their feet and the ground. Sparks sprang from water line taps when touched. Light bulbs within 100 feet (30 m) of the lab glowed even when turned off. Horses in a livery stable bolted from their stalls after receiving shocks through their metal shoes.
The most widely used electronic switch in digital circuits is the metal–oxide–semiconductor field-effect transistor (MOSFET). [2] The analogue switch uses two MOSFET transistors in a transmission gate arrangement as a switch that works much like a relay, with some advantages and several limitations compared to an electromechanical relay.
A gate turn-off thyristor (GTO) is a special type of thyristor, which is a high-power (e.g. 1200 V AC) semiconductor device. It was invented by General Electric. [1] GTOs, as opposed to normal thyristors, are fully controllable switches which can be turned on and off by their gate lead.