Industrial Engineer · phase 2 of 16
Dry Contact
Voltage-free mechanical or solid-state contact that requires an external wetting voltage.
The Explain card
- Plain English
- A dry contact is a plain switch with no voltage of its own. Whatever voltage appears on it comes from the circuit it is wired into.
- Example
- The auxiliary contact on a motor starter is dry. The input card supplies 24 V through it and reads whether the contact is closed.
- Why it matters
- Dry contacts can be wired into any voltage the contact is rated for, which makes them the safe way to pass a signal between two systems with different supplies. Feed a dry input with a wet signal and you can tie two supplies together.
- Hook
- Dry means it brings nothing to the party except the switch.
Where it sits in the deck
Phase 2: PLC I/O and Field Signals
Where the controller meets the machine: discrete and analog signals, the wiring conventions behind them, and the field devices that send them.
