What is SPDT Switch? Single Pole Double Throw Switch

An SPDT switch or Single Pole Double Throw switch is a type of switch that has only one input but two inputs. It can control two electrical circuits by making or breaking the contacts with two positions.  It has one input terminal and two output terminals. The SPDT switch not only turns Off or turns On the circuits even it also has other various functions. Such as it can change the path for the flow of current from one circuit to another circuit.

The working principle of the SPDT switch is very simple. For, example two different loads are connected to a single power source through the SPDT switch. So, we can change or turn off or turn any load at any time with this SPDT switch. At a time one load will be in off condition and another one will be in on condition. So, the SPDT switch can change the pathway of the current flow.

Here, you can see the symbol of SPDT switch.

Now, let's see the circuit diagram of SPDT switch to understand its working principle.

Here in the above wiring diagram of DPST switch, you can see two LEDs are connected to a single battery through an SPDT switch. The LEDs are named as LED1 and LED2 and the contacts of the SPDT switch are named as output contact 1 and output contact 2

The positive terminal of the battery is connected to the input terminal of the switch. The positive terminal of the LED1 is connected to the output contact 1 and the positive terminal of the LED2 is connected to the output contact 2. The negative terminals of the battery and two LEDs are connected directly.

Now, when the output contact 1 is closed to the input the LED1 will glow and LED2 will be in off condition. When the output contact 2 is closed to the input the LED2 will glow and LED1 will be in off condition.

So, the functions of an SPDT switch are to turn Off, and turn On circuits. Also, it interchanges two different loads with a single power supply. It can change the pathway of two different circuits.

You can see the use and application of SPDT switches in electronic circuits, and electrical or electronic devices. The two-way switch used in our house wiring is also an example of SPDT switch.

Read Also: 

• What is SPST Switch? Single Pole Single Throw
• What is DPST Switch? Double Pole Single Throw
• What is DPDT Switch? Double Pole Double Throw
• [Proper] Two Way Switch Connection Diagram and Wiring
• 4 Way Switch Wiring Diagram and Connection

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