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The use of variable speed drives (VSDs) for controlling motors is becoming more common, particularly because of their ability to generate energy savings. But these drives usually have specific requirements for ventilation when mounted inside a cabinet, which can compromise weather protection or ‘IP rating’ in an outdoor application.

Why do I need ventilation?

A typical variable speed drive generates a large amount of heat for its size. If the cabinet is not ventilated, the drive can overheat, causing the respective motor to shut off and potentially result in damage to the VSD and other components.

What’s the maximum IP rating I can attain with cabinet ventilation fitted?

The installation of a standard ventilation fan with grilles and filters will reduce the cabinet’s IP rating to IP54 or less. However, shrouds can be fitted over the ventilation grilles, which greatly reduce the potential for water ingress from above: this can result in an IP rating of up to IP56, which is generally acceptable for most outdoor environments.

Are there any other options?

Most VSD brands also offer models with an IP rating of IP54 or greater, for mounting outside the switchboard. The use of these drives can negate the need for ventilation and allow the IP rating of the switchboard to be increased, for example to IP66.
However, remember that even if a VSD (or other component) is rated to IP54 or more, it doesn’t necessarily mean it’s suitable for mounting outdoors – particularly in Australian sun and weather conditions.
In some applications with smaller VSDs, a sufficiently large cabinet can allow for adequate heat transfer so that ventilation is not required.