For questions about switches, i.e. electrical devices used to manually open and close an electric circuit on a routine basis.
A switch is an electrical device used to control the flow of electricity through an electrical circuit based on a manual (user) operation. Switch nomenclature varies depending on locality:
- "Single pole" is sometimes used for an ordinary On/Off switch
- A switch used as part of an arrangement for controlling a light from two locations may be referred to as "2-Way" (UK) or "3-Way" (US), or as a SPDT (Single Pole Dual Throw) switch.
- A switch used in conjunction with two SPDT switches for controlling a light from three or more locations may be referred to as a "crossover" or "intermediate" (UK), or as a "4-way" (US) switch. Note that they have internal wiring that makes them different from a DPDT (Dual Pole Dual Throw) switch -- which are also available (but rarer).
- A switch used to control two legs or phases of a branch circuit, or two branch circuits simultaneously, is called a "dual pole" switch.
- Ordinary light switches are called "snap switches". Larger switches may be "safety switches", "disconnect switches", or "fusible disconnects" -- these are used to turn on and off larger loads such as air conditioners, motors, or even entire services, and often have a facility for locking them in the off position so that equipment can be safely worked on.