When choosing a push button switch, customers may see terms such as SPST and SPDT in product specifications.
These terms describe the internal contact structure of the switch and determine how the switch connects and controls an electrical circuit.
Understanding the difference between SPST and SPDT helps customers select the right switch for their equipment.
What Is SPST?
SPST stands for Single Pole Single Throw.
It is the simplest switch contact configuration.
Single Pole: One input circuit
Single Throw: One output circuit
An SPST switch usually has two terminals and works as a basic ON/OFF switch.
How It Works
Button not pressed:
Circuit is open
Current does not flow
Button pressed:
Circuit is closed
Current flows
SPST switches are commonly used for:
Start buttons
Signal control
Simple ON/OFF operations
Basic electrical control
A push button with 1NO contact is a common example of an SPST configuration.
What Is SPDT?
SPDT stands for Single Pole Double Throw.
An SPDT switch has one common terminal and two switching positions.
The terminals usually include:
COM (Common)
NO (Normally Open)
NC (Normally Closed)
The switch can connect one input signal to two different output paths.
How It Works
Normal position:
COM connects to NC
After pressing:
COM switches to NO
This allows one button to control two different circuit functions.
SPST vs SPDT Comparison
| Feature | SPST | SPDT |
|---|---|---|
| Full Name | Single Pole Single Throw | Single Pole Double Throw |
| Function | Simple ON/OFF switching | Switching between two circuits |
| Terminals | Usually 2 | Usually 3 |
| Control Method | One circuit | Two selectable circuits |
| Structure | Simple | More flexible |
Applications of SPST Switches
SPST push buttons are often used in:
Machine start controls
Indicator switches
Simple control panels
Electronic equipment
They are suitable for applications where only one circuit needs to be turned on or off.
Applications of SPDT Switches
SPDT push buttons are used in applications requiring circuit switching, such as:
Mode selection
Signal switching
Control systems
Circuit selection
They are suitable when one switch needs to control different functions.
How to Choose SPST or SPDT?
Choose SPST when:
✓ Only one circuit needs to be controlled
✓ A simple ON/OFF function is required
✓ The application does not require switching between circuits
Choose SPDT when:
✓ One input needs to switch between two outputs
✓ Different circuit functions are required
✓ More control flexibility is needed
Conclusion
SPST and SPDT describe different contact structures used in push button switches.
SPST: A simple ON/OFF contact structure, suitable for basic control applications.
SPDT: A switching contact structure that can select between two circuits.
Selecting the correct contact type helps ensure reliable operation and proper integration into equipment.
ONPOW provides push button switches with different contact configurations, including SPST and SPDT options, for various industrial applications.
ONPOW - Professional Push Button Switch Manufacturer
