Industrial Automation

What are Dry Contact and Wet Contact and their differences?

What is Dry Contact?

  • Dry contacts are known as voltage-free contacts or potential-free contacts.
  • These contacts don’t provide any power or voltage source from the switch.
  • But power or voltage source is provided from an external source.
  • The contact current for these dry contact is less than one milli-ampere.
  • The power supply must be provided because these connectors are disrobed and don’t have energy.
  • They are known as dry contact because the relay required for dry contact can be energized or de-energized for change in input.
  • This energizing and de-energizing condition helps us to know whether the input is switched on or off.
  • The power supply required to energize the relay is connected using separate cables or we can apply a local power supply located near the relay.
  • The flow of current through dry contact is possible only during closed or shorted. But no current flows through dry contacts during the open conditions.
  • Dry contact functions like an ordinary switch to open or close the circuit.
  • In other words, these dry contacts are called passive contacts because energy is not applied to contacts.
What are Dry Contact

How to connect a dry contact relay?

  • Dry contact relay installation and connection must be done professionally by a skilled electrician or technician considering the space may be far away from the central hub or the ubiquity of different items that may interpose with the signal.

What are the Examples of Dry Contact?

Examples of dry contact are

  • Fire alarms
  • Control relays
  • Fans
  • Lights
  • Horns
  • Valves

Important Guidelines for installing a Relay:

The relay must not be installed in the following places.

  • Do not install in the open air or in an outdoor location
  • Do not install with electric breaker panels inside metallic junctions.

What is Wet Contact?

  • A contact that can be activated or energized by the same power source applied by the control circuit to change the contact is known as wet contact.
  • Wet contact is also known as the primary contact.
  • Wet contacts are commonly observed in solid-state switching devices such as sensors.
  • When power is provided to wet contact, the simple switching action will release the same supply to turn off the load device without consuming any extra power supply.
  • This wet contact works with the same potential as the potential given to energize the sensor.
  • The wet contact is turned on only when the sensor detects an object, and the output of the contact is turned off if the sensor doesn’t sense any object.

What are examples of Wet Contact?

Examples of wet contact

  • Thermostats
  • CO2 Sensors
  • Humidity sensors
  • Flow sensors, and Pressure sensors.

Differentiate between Dry Contact & Wet Contact:

The below table shows the differences between dry contact and wet contact:

Dry ContactWet Contact
Here the power is supplied by another source.Here the power is supplied by the same power source. The control circuit is used to energize the contact.
It operates as an ordinary single pole On and Off switch.It operates like a controlled switch.
It can be considered secondary contact of the relay circuit.It can be considered the primary contact of the relay circuit.
Dry contacts provide isolation between two devices.Wet contacts will not provide any isolation, but gives the same potential to control the device.
Dry contacts are called Passive contacts.Wet contacts are known as Active contacts or Hot contacts
These are available in relay circuits because these relays will not provide any intrinsic power supply to the contact.Wet contacts are utilized in the control circuits where the power is intrinsic to energize the contacts. Such as Control Panels, and Temperature Sensors.
Dry contacts will not use mercury-wetted contacts.  Wet contacts use mercury-wetted contacts.
Dry contacts provide complete isolation between two devices.Wet contact makes troubleshooting much easier because of the simplicity of wiring and the same voltage level.

What are the advantages and disadvantages of Dry Contact?

Advantages of Dry Contact:

Disadvantages of Dry Contact:

  • Requires external source to power up.
  • Not applicable for High voltage

What are the advantages and disadvantages of Wet Contact?

Advantages of Wet Contact:

  • Cabling is simple
  • Requires a minimum number of cables.
  • Consumes less power.   
  • Cabling comes with the same potential.

Disadvantages of Wet Contact:

  • Wet contacts can’t provide any isolation between two circuits.
  • Both input circuits and output circuits are dependent on each other.
  • Difficult to isolate.

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