A pull switch is a switch that breaks or makes an electric circuit by pulling a string or a chain. It is a good choice in situations where extensive electrical wiring may not be suited, such as in damp and wet areas. A pull switch also provides a very convenient and safe way to turn on or off electric power for lights and other appliances. Electrical switches are available in different types. An electric pull switch is a sequential type, like the latching push-button switch. Some light switches make use of the standby voltage across the switch to energize a night-light, seen as a small neon light or light-emitting diode (LED). Most of these night-lights are activated automatically without extra wiring. The pull switch latches alternately in the “on” position and then in the “off” position with every pull. A string switch is very common for home use, while the chain switch may offer ruggedness in special environments. In public safety situations, for instance, outdoor chain pull switches may be useful for emergency searchlights and sirens. A three-way switch connection allows the same light on/off switching at both ends of corridors or walkways. With a three-way connection, two units of two-position switches that are single-pole-double throw (SPDT) are used. For these switches, unlike the single-pole-single-throw (SPST), the SPDT has a common terminal and two wired positions. The SPST has two wired positions that make or break a single circuit, while the SPDT turns on one circuit and then another. By connecting two SPDTs so that each could break and make a circuit, the two SPDTs and an extra wiring become a three-way switch. Light switches are available in a variety of switching modes. Most of these switches are SPST, which is usually a rocker type that may be pushed into an on or off position. In electronic switches, there are tactile or touch-sensitive switch pads that detect changes in touch pad capacitance due to contact with the human skin. These switches are very convenient and require very little effort. Electronic and electrical light switches may also have continuous dimmers or step dimmers with “off” semi-bright and full bright or “on” features. Electrical dimmers have been improved using a three-terminal alternating current (AC) control device known as triode for alternating current (TRIAC). Pull switches that control high-power devices may use electromechanical or electronic relays, such as the TRIAC circuit.
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