Switches

Characteristics

There are two characteristics that make switches distinct: Throws and Poles.

1. Throws – This indicates contact-to-contact connection and the switch’s settings. For example, a double throw is a switch that operates in two unique settings (high and low).
2. Poles – This refers to the number of individual circuits the switch controls. For example, a DP or Double Pole switch has two circuits that are controlled by just one throw.

Throws and poles help provide a clear description of what a switch does. So, if the examples above are combined, it would describe a single pole, double throw switch.

Types

There are two types of switches: the basic type (mechanical and electrical) and the type according to throws and poles (SPST, DPST, SPDT, and DPDT)

• Mechanical switches need physical activation. These switches have to be pressed, touched, released, or moved through their contacts.
• Electronic switches are non-physical switches and don’t need to be physically turned on or off. They are controlled by a semiconductor.
• SPST or single pole single throw switch has one input and one output contact. It is the traditional on and off switch most people are familiar with.
• DPST or double pole single throw switch has four terminals – two input and two output contacts. It is used for simultaneous control of two circuits.
• SPDT or single pole double throw switch has one OFF position and two ON positions, so it has three terminals.
• DPDT or double pole double throw switch has two ON positions. It’s a dual ON and OFF switch. With four output and two input contacts, this type of switch is equipped with six terminals.