Stego pressure compensation and drainage devices

Pressure compensation devices and drainage devices protect electrical equipment in enclosures and switchboards from dangerous climate change and satisfy AS3000:2018.

AS/NZS3000:2018 clause 1.7.2 (i) states “Condensation issues – a breathing/pressure equalization valve shall be installed to assist with changes in humidity and drainage of moisture”. Thus, the fitting of ventilation devices is now required to all enclosures where condensation is likely to occur. This application note explains how condensation occurs inside electrical enclosures and the available solutions.

Equipment in an enclosure or switchboard requires that ambient temperature and humidity is maintained within the specified range for correct operation and optimum life expectancy.

Climate control devices such as ventilation fans, heat exchangers, heaters and air conditioning units can, when installed and operating correctly, maintain the enclosure or switchboard within the specified temperature and/or humidity range. This, however, may be insufficient to protect equipment from potential damage.

Ambient temperature and humidity changes can cause pressure differentials and condensation to form inside an otherwise sealed enclosure or switchboard. These changes can be caused by:

- the change between day time and night time temperatures

- rapid changes in the weather (particularly sudden cooling and rainfall after a hot day)

- equipment operating under varying load conditions and heating up or cooling down as a result

- the enclosure being subjected to high pressure wash down.

Such condensation is known as ‘sweating’ and all enclosures are susceptible, regardless of ingress protection (IP) rating. Enclosures and switchboards are not gas tight. Condensation can cause short circuits and corrosion that can cause equipment inside the enclosure to malfunction, eventually causing permanent damage. Pressure compensation devices and drainage devices can prevent condensation damage to installed equipment by expelling any accumulated water droplets while still maintaining the IP rating.

Note that while anti-condensation heaters are intended to keep the enclosure or switchboard temperature above the dew point (and thus prevent condensation), they may not always be able to achieve this, because heaters:

- may have been sized for the ‘typical’ scenario and may not allow for extremes of temperature or humidity beyond the ‘typical’ range

- require external power and a correctly adjusted and working thermostat

- may prevent condensation, but the humidity is still trapped inside the enclosure or switchboard.

In summary, all electrical enclosures and switchboards installed outside and/or subject to rapid ambient environmental changes are at risk of experiencing condensation issues.

Pressure compensation devices and drainage devices are completely passive and so provide a reliable, low-cost back up to help protect the valuable equipment installed in the electrical enclosure or switchboard.

Furthermore, AS/NZS3000:2018 Clause 1.7.2 requires that pressure compensation and drainage devices be installed in all enclosures and switchboards where condensation is a risk.

Principle of operation – pressure compensation devices

The example below is of a small to medium electrical enclosure being sprayed down at a chemical plant.

Without a PCD, there is a large pressure difference between the outside and inside of the enclosure or switchboard, which creates a (relative) vacuum inside the enclosure. This pressure difference can damage the enclosure sealing. Moisture penetrates at the enclosure sealing points, regardless of the IP rating. PCDs have a special membrane that is impermeable to water but allows air to enter. With a Stego PCD installed on both sides, dry air can enter the enclosure to equalise the pressure inside and out, avoiding damage to the sealing. Note that the PCD should be selected to match the IP rating of the enclosure. If a PCD with a lower IP rating is fitted, then the IP rating of the whole enclosure will be degraded to the IP rating of the PCD.


Principle of operation – drainage devices

On a hot, humid day with an abrupt cool change accompanied by rain or thunderstorms rapidly cooling the enclosure or switchboard, condensation inside is more likely and any installed heater may not be able to remove it quickly enough. Likewise, water inevitably pools near the sealing points and may penetrate the seal. Eventually the water will pool at the bottom of the enclosure.

With no way to exit the enclosure or switchboard, the accumulated water is an electrical shock and fire hazard and may cause corrosion. A Stego drainage device has a special membrane that that allows drainage through capillary action and can remove up to 200mL/hr of water to drain out of the enclosure, thus safely removing the hazard.

Pressure compensation plugs are available in plastic and stainless steel, both of which will maintain an IP66 rating. The DD084 drainage device is available in plastic.


The fitting of pressure compensation and drainage devices is now mandated by AS3000:2018 clause 1.7.2 to all enclosures and switchboards where condensation is likely to occur.

Pressure compensation devices and drainage devices are an inexpensive and easy-to-install solution to prevent condensation and moisture build-up in electrical enclosures and switchboards while satisfying the wiring rules. These completely passive devices require no power and are essentially maintenance free for the life of the enclosure.

For more information, please call your local NHP Account Representative or email us:

Australia 1800 647 647

New Zealand 0800 647 647

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