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In contrast to a simple light switch, which is a single pole, single throw (SPST) switch, multiway switching uses switches with one or more additional contacts and two or more wires are run between the switches. When the load is controlled from only two points, single pole, double throw (SPDT) switches are used.
For example, a "2-pole" switch has two separate, parallel sets of contacts that open and close in unison via the same mechanism. The number of "throws" is the number of separate wiring path choices other than "open" that the switch can adopt for each pole. A single-throw switch has one pair of contacts that can either be closed or open.
Below is a list of typical switch configurations and usage: Single pole, double throw (SPDT or 1:2) switches route signals from one input to two output paths. Single pole double throw (SPDT) switch from Agilent Technologies. Multiport switches or single pole, multiple throw (SPnT) switches allow a single input to multiple (three or more) output ...
Reed switch diagrams from Walter B. Ellwood's 1941 patent, [4] Electromagnetic switch. It illustrates a single pole, double-throw (SPDT) device. Descriptions from the patent text are as follows: Fig. 1 - device shown in nonoperated position Fig. 2 - device shown in operated position Fig. 3 - cross-section 1 - glass envelope 2 - terminal
Double switching is a crucial safety engineering practice in railway signalling, wherein it is used to ensure that a single false feed of current to a relay is unlikely to cause a wrong-side failure. It is an example of using redundancy to increase safety and reduce the likelihood of failure, analogous to double insulation. Double switching ...
Simplified single line diagram of a single-phase transfer switch to select either 'city' (utility) power or local generator power 3-phase Intelligent transfer switch. A transfer switch is an electrical switch that switches a load between two sources. Some transfer switches are manual, in that an operator effects the transfer by throwing a ...
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A Single-Pole, Single-Throw (SPST) mercury switch on millimetre graph paper, device length approximately 1.5 cm Another mercury switch design. A mercury switch is an electrical switch that opens and closes a circuit when a small amount of the liquid metal mercury connects metal electrodes to close the circuit. There are several different basic ...