Dry Contact Vs Wet Contact

I am often asked what the difference between dry and wet contact is. In this post, I will explain the difference between the two, their applications, and how they compare.

The main difference between dry and wet contact is that dry contacts open and close a separate isolated circuit, and the output power is completely removed from the input power.

Meanwhile, for wet contacts, the output power is immediately supplied along with the input and is only sent to the output terminal when the switching action has occurred.

Before we compare dry contact vs wet contact, let’s analyze each type of contact and what they can do.

What are Dry Contacts?

In the dry contact switch method, an engineer must externally provide the source of electricity to be sent to the load, usually through a ‘common’ wire.

This is the terminology used in a relay, where the contact wires are labeled common (C), normally open (NO), and normally closed (NC).

Examples of dry contacts

Examples of dry contact are

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

Advantages of Dry Contact

  • Operates in any orientation without draining.
  • These are well applicable to portable equipment.
  • Less Susceptible to Leakage
  • It gives complete isolation.

Disadvantages of Dry Contact

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


Wet Contacts

Wet contacts like sensors are most likely to be seen in solid-state switching. Once power is provided, the simple switching action sends this same supply power to the load device. No extra common power wires are required.

Advantages of Wet Contact

  • Wiring is simple
  • Requires a minimum number of wires.
  • Consumes less power.   
  • Wires come 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.

Examples of wet contacts

Here are some examples of wet contacts

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

Dry Contact Vs Wet Contacts: Comparison table.

Dry Contact

Wet Contact

Another source supplies the power. The same power source supplies the power. 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 a 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 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.
It is more complicated to wire a dry contact than a wet contact. It is easier to wire a wet contact.


FAQ: Dry Contact vs Wet Contact

Is a thermostat a dry contact?

Thermostats are wet contacts. They get their power from the circuit board, which directly influences the circuit’s activity.

Are PLC modules dry or wet contacts?

PLC modules are always dry contacts, regardless of whether they are relay or digital output types.

Is a dry contact normally open or closed?

There are two main types of dry contact: passive and normally open and the other is passive and normally closed.

It is characterized by the fact that it does not carry a power supply but has a certain capacity.

Key takeaway: Dry Contact vs wet contact

The main difference between dry and wet contact is that dry contacts are not directly provided with power from the switch.

They are used in switching devices that provide isolation and offer various output voltage options. 

Wet contacts are automatically given power when the switch has power, and the main advantages are the simplicity of wiring and the consistency of voltage levels, making troubleshooting much easier.

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