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Condensation - the creeping danger

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Article created for DesignSpark by Matthias Schneider, Sales Engineer at Stego GmbHIn

Humidity - condensation - corrosion: This chain of adverse conditions often adds up to cause failure in sensitive electrical and electronic components. The use of modern electric enclosure heaters is an effective and economic countermeasure that addresses these frequently neglected causes of defect and avoids damage or even breakdowns.

Operational reliability and longevity are attributes every customer expects from a panel or enclosure. The controllers increasingly feature sensitive electronics. For some electronic components, the service life is directly related to the ambient temperature. This requires the interior temperature of enclosures to be lowered and unwanted excess heat to be removed. This is achieved through ventilation via filter fans.

However, the danger arising from condensation in enclosures is often disregarded, even when the resulting defect characteristics are usually very dramatic. Short circuits cause damage in individual units that must then be replaced. This cause of defect occurs - under certain climate conditions - even in enclosures with high IP ratings.

Condensation - a rarely recognised cause of faults or even complete breakdowns of an entire control system.

In combination with aggressive gases and dust particles, condensation causes atmospheric corrosion. Affected are, e.g.:

  • bus bars
  • contactors
  • relays
  • protective motor switches
  • transformers
  • frequency inverters
  • programmable controls
  • semiconductors/circuit boards
  • solder, crimp and screw connections

Condensation is thus a source of faults that must be taken seriously. The biggest risk in practice occurs when relatively high humidity and temperature fluctuations coincide in an encapsulated enclosure. Failure causes triggered by condensation in systems can be:

  • changing contact resistances
  • indefinable stray currents
  • reduced insulation properties
  • arcing up to total short circuit
  • corrosion occurring

There's something in the air

Humidity arises when the sun extracts water from waterways and plants by evaporation. This share of water vapour in the atmospheric air is referred to as "absolute" humidity (in g/m³). How much water can be stored in the air depends on a variety of factors, such as temperature or air pressure. The higher the air temperature, the more invisible water parts can be absorbed by and stored in the air. The ratio of "absolute" humidity to the max. possible humidity is referred as "relative" humidity (in %). At 100% RH, the air is saturated and the so-called dew point is reached. No further water vapour can be stored in the air. The excess water vapour share is dumped into the environment as condensation.

Dew - refreshing for nature, devastating for technology

At constant absolute humidity (water quantity in g/m³) and falling temperature, the air becomes saturated and can no longer hold the water vapour: the dew point is reached and fine water droplets are deposited. This process can easily be observed on windows, spectacles and drinking glasses when condensation occurs on the cold surface. This is when the danger of component failure in enclosures begins.

Outdoor installations are particularly at risk: condensation already forms as a result of temperature changes between mild daytime temperatures and overnight cool down, but even more so as a result of seasonal climate change or sudden temperature drops - such as during thunderstorms in summer.

Even in indoor installations, temperature changes triggers condensation. The culprits are bus bars, relays and other heat-generating installations mentioned at the beginning that work in a day-night cycle. If these are switched off at night, they no longer heat the air inside the enclosure. This cools down and the relative humidity rises. The consequence is the formation of condensation.

Corrosion even without condensation

The formation of condensation only starts when a relative humidity of 100% is reached. But even values lower than that can present a danger for enclosures. Corrosion can already occur at much lower values. This is the result of various long-term studies. The empirical limit thus determined is at around 65% RH. From this threshold on, one has to expect corrosion in panels and enclosures, even without condensation being formed.

Optimal conditions can only be achieved by constant temperature. Condensation and corrosion are not the only factors that significantly reduce the lifetime of the components - so does mechanical stress brought about by continuous temperature fluctuation.

The "life insurance" for panels & enclosures: electric enclosure heaters

The state-of-the-art solutions are electric enclosure heaters that have been developed specifically to avoid condensation and temperatures that are too low or fluctuate too much. The air in the enclosure is heated to the point where it can hold the entire water vapour and condensation is avoided. Without a heater, the relative humidity increases and condensation occurs on components.

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Stego Touch-Safe heater series CS 060

Modern heaters for enclosures, such as the STEGO Touch-Safe heater series CS 060, create maximum air circulation at extremely low energy consumption, even without an integrated fan. This useful natural convection is achieved through the chimney-like construction of the heater profile. Tube or panel radiators, ceramic resistors or even light bulbs are thus rather unsuitable as heaters.

Stego Touch-Safe heater series CS 060

The full list of products is as follows: (048-9276) , (048-9260) , (048-9270) , (048-9286) , (048-9220) , (048-9254)

A high packing density or higher temperature requirements in outdoor use demand fan-operated heaters (also called fan heaters) with forced air circulation. These are available with heating capacities between 100 and 1,200W. The new STEGO compact fan heater types CSL028 & CSF028 are ideal for space-constrained applications.

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CSF028 Stego compact fan heater with thermostat

The full list of products is as follows: (812-9651) , (812-9660) , (912-9663) , (812-9667) , (812-9673) , (812-9376) , (812-9679) , (812-9682) , (812-9385) , (812-9389)

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CSL028 Stego-Compact Fan Heater

The full list of products is as follows: (697-4382) , (697-4386) , (697-4389) , (697-4392) , (697-4395) , (697-4398) , (697-4405) , (697-4409) , (697-4411) , (697-4415) , (697-4418)

With control units such as thermostats, hygrostats and hygrotherms (combination device of thermostat and hygrostat) in connection with a heater, even extreme fluctuations of temperature and high humidity are easy to manage. For applications used internationally, it is advisable to control a heater in combination with a hygrostat or electronic hygrotherm. This controller responds directly to the actual humidity and always switches on the heater at the correct time, regardless of climatic conditions. This is the perfect way to avoid condensation. The heating capacities of the heaters and fan heaters can be dimensioned between 10 and 1,200W as required by the application.

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ETF012 Stego Electronic Hygrotherm Sensor

The full list of products is as follows: (785-8083) , (785-8089) , (785-8092) , (785-8095)

Conclusion: Enclosure heaters are a reliable protection against condensation and temperatures that fluctuate or are too low. When comparing the cost caused by failures to the purchase price of enclosure heaters and controllers, the latter represent little additional cost that nevertheless makes a big difference.

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