5G communication testing, wireless terminal automated testing
Aerospace communication systems
Precision measurement equipment, radio frequency signal control of radar transmitters
Communication and navigation systems
Optical communication module-related testing
Interconnection of wireless communication base stations
SPST (Single-Pole Single-Throw) is a simple on/off switch with one input and one output. SPDT (Single-Pole Double-Throw) routes one input to one of two outputs — like a light switch or selector. DPDT (Double-Pole Double-Throw) has two independent circuits, each switchable between two outputs — perfect for reversing polarity, switching between two sources, or H-bridge control.
The terms "pole" and "throw" describe the electrical structure of a switch:
A switch with more poles can switch multiple signals simultaneously. A switch with more throws gives more routing options. Together, they define what a switch can do.
SPST has two terminals. When the lever is up (open), no current flows. When down (closed), Terminal A connects to Terminal B.
An SPST switch is the simplest form: a single pole that can be either open or closed. It functions exactly like a light switch in your home — on or off, no nothing to.
The SPST symbol shows two terminals connected by a switch lever. When the lever is drawn making contact, the switch is closed; when it is drawn angled away, the switch is open.
SPDT has three terminals: one common and two throws. The lever routes the common to either T1 or T2.
An SPDT switch has one pole (one common input) and two throws (two selectable outputs). It selects between two destinations, like a railway switch routing a train.
DPDT has six terminals and operates two independent SPDT switches in sync, allowing polarity reversal or simultaneous routing of two circuits.
A DPDT switch has two poles and two throws. It is essentially two synchronized SPDT switches operated by one actuator. DPDT is useful when you need to switch two signals together — for example, reversing the polarity of a DC motor or switching between two audio sources and grounds simultaneously.
| Parameter | SPST | SPDT | DPDT |
|---|---|---|---|
| Number of Poles | 1 | 1 | 2 |
| Number of Throws | 1 | 2 | 2 |
| Number of Terminals | 2 | 3 | 6 |
| Switch States | 2 (on/off) | 2 (A or B) | 2 (forward/reverse) |
| Circuits Controlled | 1 | 1 of 2 | 2 of 2 simultaneously |
| Typical Use | Power on/off | Source selection | Polarity reversal |
| Code | Name | Use |
|---|---|---|
| DPST | Double-Pole Single-Throw | Two simultaneous on/off switches |
| 3PDT | Triple-Pole Double-Throw | Three synchronized SPDT switches (e.g., guitar wiring) |
| 4PDT | Quad-Pole Double-Throw | Four synchronized SPDT switches |
| SP3T – SP12T | Multi-throw | Selectors with 3 – 12 positions (rotary switches) |
SPST is the simplest: a single pole with one throw. It functions as a basic on/off switch and has only two terminals.
SPDT has one pole switching between two throws. DPDT has two poles, each switching between two throws, all operated by one actuator. DPDT effectively gives you two synchronized SPDT switches.
Yes. By wiring the motor to one set of throws with reversed polarity on the other set, a DPDT switch flips the motor's direction with each throw.
A momentary switch returns to its default position when released — like a doorbell button. A maintained (latching) switch holds its position until actuated again — like a light switch.
Yes. Using a higher voltage or current rating than required is generally safe and improves reliability. The reverse (using an underrated switch) is dangerous.
High-tech Enterprise, Feifeng Talent
Chief Engineer Wang graduated with a master's degree in high-power microwave from the Institute of Electronics, University of Chinese Academy of Sciences.
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