A switch is just a gap you can close. But choosing the right one matters.
A switch opens or closes a circuit. Different types suit different jobs.
1. Poles and throws
- Pole: how many separate circuits the switch controls.
- Throw: how many positions each pole can connect to.
| Type | Means |
|---|---|
| SPST | Single pole, single throw. Simple on/off. |
| SPDT | Single pole, double throw. Switches one feed between two outputs. |
| DPST | Two circuits on/off together. |
| DPDT | Two circuits, each switched between two outputs. |
2. Momentary or latching
- Latching stays where you put it (light switch).
- Momentary only works while you hold it (horn button).
3. Illuminated switches
Lit switches often have a third terminal for earth so the light works. Wire them as the diagram on the switch shows.
4. Current ratings
A switch has a maximum current, and often a lower rating for DC than AC. For heavy loads, use the switch to run a relay instead. See How Relays Work.
5. Quick summary
- Poles = circuits. Throws = positions.
- Check the DC current rating.
- Use a relay for big loads.
240V AC mains can kill. In Australia, work on household mains wiring must be carried out by a licensed electrician. Low-voltage DC can still deliver very high current, so treat batteries with respect.
