Electrical enclosures: Warm and dry keeps condensation away

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Condensation in an electrical enclosure

How does condensation happen?

Condensation is caused by warm moist air coming into contact with a surface that is colder than the air’s dew point. So what happens in an electrical enclosure?
In humid conditions the warmer air is the more water vapour it holds. When warm air inside an enclosure comes into contact with the enclosure’s colder casing, it cools. And it may chill to a point where it can no longer hold water vapour. The vapour, suspended as a gas, turns into water. The air has reached its “dew” point and condensation occurs.
Outdoor equipment is particularly prone to condensation, especially when it is not thermally insulated. That is due to the change in temperature as daytime warmth turns into the chill of night.
And with the extreme weather and wild temperature swings of recent years, outdoor enclosures are even more highly exposed to the risks of condensation.
Condensation may also form in indoor enclosures, of course, when humidity levels are too high and temperatures swing sharply.

Why is condensation dangerous?


When condensation gathers on the inside surface of an enclosure, the risks of malfunction are high.
It causes premature ageing, rusting, short circuits, and breakdowns in electric and electronic equipment that is housed in enclosures.
The consequences can be serious in for, example, critical outdoor applications like wind turbines and solar power installations.

How can condensation be prevented?

You can design humidity control into your enclosure. Enclosures that are tightly sealed and large enough to allow airflow reduce the risk of condensation.
Essentially, however, you prevent condensation by keeping relative humidity below 60% and controlling sudden temperature variations.

Relative humidity?

Its the amount of water in the air at a given temperature expressed as a percentage of the amount of water the air could hold.

What can you do when condensation does occur?

The most effective solution combines heaters with control devices like hygrostats, thermostats or hygrotherms.
Thermostats trigger heaters when temperatures fall below a set point. Hygrostats, however, turn heaters on when humidity rises above a given threshold. Hygrotherms do both.
Using hygrostats to control your heater is considered more energy efficient. However, they are much more expensive to buy than thermostats, so compare the solutions carefully before you choose.

When would you use a hygrotherm?

In some parts of the world, temperatures fall so low in winter that they are below the operating temperatures of control panel components. Similarly, in summer, dew points occur at high humidity levels.
This is where hygrotherms come into their own. With hygrotherms, both low ambient temperatures and high relative humidity levels trigger the heater.

Why are some heaters so slim?

Because small is beautiful. Electronic and electric parts are getting ever smaller. So, too, are enclosures. Yet, as we mentioned, enclosures should also be airy enough to stop condensation forming.
The answer is ultraslim resistance heaters – some are only just over 1.5 mm thick. These slimfit devices kick in at low temperatures and can be mounted any way up.

What do you think is the most effective condensation solution? Please share. Or maybe you’d just like to know more? 

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  • Circulation d’air et résistance permettant de maintenir la température intérieure quelques degrés plus élevée que la température extérieure.

  • Rajanikanth JKT

    11 years ago

    Instead of having heaters it’s better to have dehumidifier through which you can control the humidity of air and through which you can maintain required temperature & humidity. Like air condition if you have dehumidifier the air within the control panel room will recirculate through dehumidifier. Also please note that especially in winter season the humidity will be very low. You may observe in winter seaon the human body will get dry need moisturiser and some area require humidifier.


  • Mahersa Ali

    7 years ago

    A customer is having a worry with condensation inside his 24 kV IPB, on its connection point to transformer. He’s thinking of making a hole and pipe on Transformer hv bushing flange. But it will just create a bigger space. Any solution with heater? One that is slim enough not to obstruct the IPB clearance.

  • Muhammad Usman

    7 years ago

    Facing condensation in the heater electrical control box which is installed in the AHU (air handling unit). Kindly advise how we can control condensation issue.

  • John Kealy

    7 years ago

    I have been engaged in designing electrical power and lighting systems for commercial and industrial facilities since 1965. One caveat I learned early on is you should never install an electrical power panelboard flush in an exterior wall of a building because of the likelihood of condensation forming.

  • Dear Sir,
    We are facing problem condensation in 33kV cable box of 25MVA 33/6.9kV transformer, we are installed 2 Nos. of 80W heaters & control through thermostat.
    We also installed one digital humidity & temperature metre for measure humidity & temperature inside the cable box
    In summer, humidity not cross 63% but humidity reach 70% in monsoon.
    What is the measure taken for prevent from condensation.

    We are facing two times flash over in cable box before and after installation of Heaters.

    • Abderrahmane AGNAOU

      6 years ago

      The installation of heaters is a good solution. You can use a Hr / T° controler that will switch on the heaters only when there is a condensation risk.

  • Ted Murphy

    6 years ago

    The article failed to mention how the cabinet material contributes to this problem. Cold rolled or stainless steel, as better conductors of heat, dramatically increase the likelihood of condensation forming vs Lexan or other non thermally conductive materials. So material choice and adequate ventilation can reduce or eliminate the need for other techniques, especially for smaller control enclosures frequently used by utilities.

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