What Is a Switch?
A switch is an electromechanical component that opens and closes a circuit's current path by hand. It completes or breaks the circuit by physically joining and separating its contacts.
Pole and Throw
Switches are defined by pole and throw. The pole is how many separate circuits the switch controls at once; the throw is how many different points each pole can connect to. For example, SPST is single-pole single-throw, SPDT is single-pole double-throw.
| Type | Meaning |
|---|---|
| SPST | On/off (single circuit) |
| SPDT | Selects one of two paths |
| DPDT | Routes two circuits together |
Momentary and Latching
A latching switch keeps its position after pressing (like a light switch). A momentary switch conducts only while held down; push buttons are in this class.
Switch Types
Common types: toggle, tactile button, DIP switch for hardware setting, micro/limit switch for position sensing, and the magnetic reed relay.
Current/Voltage Limit
Every switch's contacts have a certain current and voltage rating. If this limit is exceeded, there's arcing, heating and sticking at the contacts.
Where Is It Used?
Device on/off, mode selection, panel controls and user interfaces. Across a wide range from signal level to mains power.
Contact Material
Switch contacts can be silver alloy or gold-plated. Silver works well with low resistance in power switching; gold gives reliable contact against oxidation on low-level signals. The wrong contact material can lead to a failure to conduct over time in low-current circuits.
Common Mistakes
- Overcurrent: high power shouldn't be given to a signal switch.
- Inductive load: arc-suppression must be taken with loads like motors/relays.
- Bounce: contact bounce must be filtered in logic circuits.
Frequently Asked Questions
What does SPST mean?+
Does a switch also select direction?+
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