A dry contact (also known as a volt-free contact or potential-free contact) is defined as a contact in which power/voltage is not directly provided from the switch but is instead always being supplied by another source. Dry contacts are known as passive contacts, as no energy is applied to the contacts themselves.
A dry contact operates just like an ordinary single-pole ON/OFF switch: when closed, it completes the circuit and allows current to flow; when open, it breaks the circuit and stops current flow. It acts as a secondary set of contacts in a relay circuit, never making or breaking the primary current being controlled, which means it provides complete electrical isolation between devices.
Why Dry Contacts Are Ideal for Wireless Remote Control ?
A dry contact output wireless remote switches (consisting of a transmitter and receiver) is the industry standard for versatile, safe remote control. Here’s why dry contacts are the preferred choice:
Isolation & Safety: They fully isolate your remote control system from high-voltage loads (like 110V/220V pumps or motors), protecting your devices from voltage spikes or short circuits.
Versatility: Since they’re voltage-free, a single dry contact remote receiver can control loads at 12V, 24V, 110V, or 220V—no need for different models for different voltage systems.
Compatibility: They work seamlessly with PLC, smart home hubs, fire alarms, burglar alarms, and building management systems (BMS).
Differences between dry contact and wet contact:
| Feature | Dry Contact | Wet Contact |
| Power Source | Always supplied by an external circuit (no power from the switch itself) | Powered by the same circuit that controls the contact |
| Function | Acts as a simple ON/OFF bridge for an external circuit | Provides power directly to the device being controlled |
| Isolation | Provides full galvanic isolation between devices | No isolation (same power for control and load) |
| Common Uses | Relay outputs, PLC inputs, wireless remote switches, alarm systems | Sensors (temperature, proximity, airflow), control panels |
| Nickname | "Passive" contacts | "Active" or "Hot" contacts |
| Relay Type | Mercury-free relay contacts | Mercury-wetted relay contacts |
| Key Advantage | Complete electrical isolation | Simplified wiring & troubleshooting (same voltage level) |
Dry Contact Relay & Wireless Remote Control Applications
In a dry contact relay, the contacts open or close without any intrinsic voltage—this makes them perfect for wireless remote control systems that need to interface with diverse home and industrial devices.
Dry contacts are used in all types of relay, including a solid-state relay. One of the advantages of using dry contact in a relay that the relay provides a wide variety of output voltage levels. For example, a relay with a 24V coil, a dry contact will allow controlling the load at any voltage level.
How Does a Dry Contact Work in a Wireless Remote Switch ?
A wireless remote control system consists of a transmitter (remote control) and a receiver. In a dry contact output remote control system, the receiver does not supply power to the output—it only provides a dry contact (volt-free, passive switch).
Here is how it works step by step:
When you press the button on the transmitter, the transmitter sends a wireless RF signal to the receiver.
The receiver receives the signal and triggers its internal relay.
The relay opens or closes the dry contact output, just like a simple manual switch. This dry contact connects to your device’s control circuit (such as lights, motors, linear actuators, pumps, electric solenoid valves, etc).
Since the dry contact is passive and isolated, it safely triggers your device without affecting its power supply.
In short, the dry contact acts as a bridge between your wireless remote system and the equipment you want to control. It works with any voltage (12V, 24V, 110V, 230V) and any device that accepts a switch input.
How to Implement a Dry Contact Remote Control System?
If you need to remotely control lights, then this series of dry contact remote control switch kits is the best solution:
Remote Light Switches
Wiring Diagram:
Connect the light to the receiver and plug the receiver into a power source.
Press the button on the remote control to turn the light on.
Press the button again to turn the light off.
If you need to remotely control a motor, then this series of dry contact remote control switch kits is the best solution:
Remote Switches for Motor
Wiring Diagram:
Connect the motor to the receiver and power it.
Press the UP button on the remote to make the motor rotate forward. Press the STOP button to stop the motor.
Press the DOWN button to make the motor rotate in reverse. Press the STOP button to stop the motor.
If you need to remotely control a water pump, this series of dry contact remote control switch kits is the best solution:
Pump & Tank Remote Switches
Wiring Diagram:
1) Control pump by transmitter CC-2:
Press button A of the transmitter CC-2, the relay of receiver is activated, and the pump is turned on.
Press button B of the transmitter CC-2, the relay of receiver is deactivated, and the pump is turned off.
2) Automatically control pump by transmitter CC-2N-2 & Water Level Sensors:
When the water reaches the low water level, two wires of the water level sensor 1 is connected, the transmitter CC-2N-2 automatically emits a wireless signal "ON", which is equivalent to the function of the red button on the transmitter. When the receiver receives this wireless signal, it will turn on the pump motor to pump water into the tank.
When the water reaches the high water level, two wires of the water level sensor 2 is connected, the transmitter CC-2N-2 automatically emits a wireless signal "OFF", which is equivalent to the function of the black button on the transmitter. When the receiver receives this wireless signal, it will turn off the pump motor to stop pumping water.
You also can press red button or black button on the transmitter to turn on / off the pump.