Usually contact combinations are divided into 4 types, such as：
- SPST (Single Pole Single throw)
- SPDT (single pole double throw)
- DPST (double pole, single throw)
- DPDT (double pole double throw)
✔SPST (Single Pole Single throw)
SPST is a most basic normally open switch with two terminal pins, which are usually used to connect or turn on and off the current in the circuit. The most common CDOE brand’s normally open button is the IP65 waterproof GQ series.
The application of the SPST switch is the light switch shown in the figure below. Usually, this type of switch has an output and input function, and does not distinguish the type of terminal pins. ON/OFF switch, when the switch in the circuit below is turned on, current will flow through the two terminals, and the light or load in the circuit will start to work. When the switch is closed, no current flows through the two terminals.
✔SPDT (single pole double throw)
The SPDT switch is a three pins terminal switch, one terminal is used as input and the other two terminal are used as output. The metal buttons with one opening and one closing will have: C terminal (Common foot), NC (Normally Closed foot), NO (Normally open foot). He can be connected to one or the other of the two, and the customer can solve it according to the actual needs. The button series that our company supports one opening and one closing include (16mm mounting hole, 19mm mounting hole, 22mm mounting hole, 25mm mounting hole); S1GQ series (19mm, 22mm, 25mm, 30mm)，xb2/lay5 series .,etc
The switch application of one normally open and one normally closed switch is mainly designed to three circuits, which are used to turn on and off the lights at the upper and lower positions of the stairs. In the circuit below, when switch A is activated, only A will light up and light B will go out. When switch B is activated, only B will light up and light A will stop working. One of the circuits is to control the lighting effect through a SPDT switch button.
✔DPST (double pole, single throw)
The DPST switch is also known as a two normally open button switch, which means that one DPST button switch controls two separate circuits at the same time. Two normally open buttons will have four pins terminal, two common terminal, and two normally open terminal. When this button switch starts to work, the current starts to flow through the two circuits. When the button stops working, the two circuits will also be at the same time stop.
✔DPDT (double pole double throw)
The DPDT switch is equivalent to having two SPDT switches, that is, two 1no1nc function push button switch, which means that there are two independent circuits. The two inputs of each circuit are connected to the two output sections, the switch position controls the number of ways, and each contact can be routed from both contacts.
When it is in ON-ON mode or ON-OFF-ON mode they work like two discrete SPDT switches worked by the similar actuator. At a time only two loads can be ON. A DPDT switch can be used in any application that needs an open & closed wiring system.
