# Electrical Basics – Switches and Contacts

## Electrical Basics – Switches and Contacts

In this video, we talk about some more electrical basics with a focus on switches and contacts. Bryan describes what they do and offers some practical ways to remember open vs. closed switches as well as pole vs. throw.

We can think of switches as police officers who direct traffic; the latter tells cars and people when to stop and go. Switches more or less control when electrons stop or go. The opening or closing of a switch is kind of like the opening or closing of a drawbridge; traffic starts when the drawbridge is closed, and it stops when the drawbridge opens.

The pole of a switch is the part that moves, and it’s usually long and thin like other types of poles. A single-pole switch has one pole, and a double-pole switch has two poles. The throw refers to where the switch can connect; single-pole switches only connect one way (with the other way being open), and a double-pole switch connects in both directions and can complete the path in either one. We identify switches by their poles and throws; an SPST is a single-pole single-throw switch, and a DPDT is a double-pole double-throw switch. (SPDT would be single-pole double-throw.)

Contactors and relays also have poles and throws. A two-pole contactor may only have a single throw, but a 90-340 relay is typically a DBDT power-passing device. A 90-340 relay controls the passing of power depending on how the electromagnetic coil is energized, but a standard switch allows you to control power manually.

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