What are the common types of circuits for switches?

  There are two terms that can be used to describe circuits in switches. They are 'pole' and' throws'. 'pole' refers to the number of circuits present in the switch. A single pole switch only has one active circuit at a time. The term 'throw' refers to the number of digits that a pole can be connected to.

  Single pole single throw switch (SPST): This switch has a single input and a single output, used to control the power output in one direction. For example, a household light switch is a typical single pole single throw switch. The schematic diagram of the single pole single throw switch is shown below: there are two connection methods for the switch: normally open (NO) and common terminal (C). Once the switch is enabled, the circuit closes.

  Single pole double throw switch (SPDT): This switch has a single input and two different outputs, which can control the power supply to output in two different directions. A single pole double throw switch consists of a moving end and a stationary end. The moving end is the so-called "knife", which should be connected to the incoming line of the power supply, that is, the receiving end, usually connected to the handle of the switch; the other two ends are the two ends of the power output, that is, the so-called stationary end, which are connected to the electrical equipment.

  Double pole double throw switch (DPDT): This switch can control two circuits, and each operation will switch between the two contacts. For a double pole double throw (DPDT) switch, a single switch can control two circuits, with each switch switching between two contacts

  Although SPST, SPDT, DPST, and DPDT are the most common types of switch circuits in our daily lives, theoretically there is no limit to the number of switches in terms of the number of poles and throws. If there are two or more poles or throws, use numerical labels instead of "S" or "D". For example, manufacturers may label a 3 pole 4 throw switch as a 3P4T switch. Similarly, the double pole six throw switch can be represented as DP6T.