Dry contact simply operates like an ordinary switch that opens or closes the circuit. When the contacts are closed the current flows through the contacts and when the contacts are opened no current flows through the contacts.
It can be referred to as the secondary sets of contacts of a relay circuit which does not make or break the primary current being controlled by the relay. Hence dry contacts are used to provide complete isolation. The dry contact is shown in the below figure.
Dry Contact
Dry contacts are commonly found in the relay circuit. As in a relay circuit, there is no external power directly applied to the contacts of the relay, the power is always being supplied by another circuit.
Dry contacts are primarily used in low-voltage (less than 50 V) AC distribution circuits. It can also be used to monitor alarms such as fire alarms, burglar alarms and alarms used power systems.
Differences between dry contact and wet contact:
| Dry Contact | Wet Contact |
| Dry contact is one in which the power is always being supplied by another source. | Wet contact is one in which the power is being supplied by the same power source that the control circuit is used to switch the contact. |
| It can operate as an ordinary single-pole ON/OFF switch. | It operates like a controlled switch |
| It can be referred to as a secondary set of contacts of the relay circuit. | It can be referred to as the primary set of contacts. |
| Dry Contacts is used to provide isolation between devices. | Wet contacts provide the same power for controlling the device. Hence it does not provide isolation between devices. |
| Dry contacts are also known as “Passive” contacts. | Wet contacts are known as “Active” or “Hot” contacts. |
| It is commonly found in the relay circuit because the relay does not supply any intrinsic power to the contact. | It is used in the control circuit where the power is intrinsic to the device to switch the contacts. Example: Control Panel, temperature sensors, air-flow sensor, etc. |
| Dry contacts mean a relay that does not use mercury-wetted contacts. | Wet contacts mean a relay that uses mercury-wetted contacts. |
| The main advantage of the dry contacts is that it provides complete isolation between the devices./s | The main advantage of the wet contact is that it makes troubleshooting much easier because of the simplicity of wiring and the same voltage level. |
Dry Contact Relay
In a dry contact relay, the contacts are opened or closed without using any voltage. Hence, we can control the dry contact relay at any voltage level.
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. This cannot be achieved by the wet contacts because the wet contacts use the same voltage level to control the load.
Dry contacts are used in PLC modules in which input voltage 24V is provided to the input of PLC modules and output is provided with separate control voltage 5V from the processor.
Wet Contact Relay
A thermostat is the most common example of a wet contact. A thermostat has the same power supply to power the control and its contact, it means that the power supply directly provides power to the control circuit and its contact.
Wet contacts are commonly found in solid-state switching’s, such as proximity sensors, temperature sensors, and air-flow sensors, in which the same voltage levels are provided to the sensor and the load, no extra common power wires are required, also the power consumption of the sensor and the load is very small.
Here are some dry contact relay remote control switches. If you are interested, you can click the link to buy:
DC 1 Channel Dry Contact Relay Switch
AC 1 Channel Dry Contact Relay Switch
DC 2 Channels Dry Contact Relay Switch
AC 2 Channels Dry Contact Relay Switch