Wet Contact (Powered Contact)
- Definition: A wet contact is a contact that supplies voltage or current when it changes state (open/close).
- How It Works:
- The voltage is supplied internally by the relay or control system.
- When the contact closes, it sends voltage to the external circuit.
- Often used where the control system provides its own signal to the connected device.
Example:
- A relay output that provides 24V DC to an alarm or indicator when activated.
- Often used in Fire Alarm Systems or security circuits where the system itself powers the contact.
Dry Contact (Potential-Free Contact)
- Definition: A dry contact is a contact in a relay or switch that does not provide any voltage or current by itself. It acts as a simple mechanical switch that opens or closes a circuit.
- How It Works:
- The external device or control system supplies the voltage or signal.
- When the relay is energized or de-energized, the contact either completes or interrupts the external circuit.
- No power is sourced from the relay itself.
Example:
- Connecting a relay’s NO (Normally Open) or NC (Normally Closed) contact to an external circuit that uses 24V DC or 230V AC to control an external load.
- Used in PLCs, alarm systems, and external circuit control.
Key Differences:
| Feature | Dry Contact | Wet Contact |
|---|---|---|
| Power Source | External circuit | Internal source of relay |
| Voltage Supply | No voltage on contacts | Voltage present on contacts |
| Application | Control external load | Trigger signal directly |
| Safety | Safer (no power) | Needs isolation for safety |
Field Wiring Consideration:
- Dry Contact: Ensure proper voltage and current rating for external devices.
- Wet Contact: Match voltage and current requirements to the field device, as the relay supplies the power.
Leave a Reply