Is enough consideration given to the protection rating of circuitry and switchgear enclosures? Graham Fox looks at the areas of an enclosure that can make the difference.
Protecting circuitry, electrical connections, wiring for displays, manual switch gear, sensors and breakers are the basic functions of an electrical enclosure, but is enough consideration given to the protection rating of that enclosure? The difference between an electrical enclosure offering IP54 and IP65 protection can make the difference between a well specified junction box that meets cost pressure and protection requirements and a failed installation due to moisture ingress, condensation or dust build up in a relatively normal working environment. The IP rating of an enclosure is dictated not only by the enclosure itself, but also by its fixing method, lid sealing and cable entries.

After the 'IP' (Ingress Protection) part of an enclosures protection rating, the first number equates to the protection offered by the box as regards solid objects from screwdrivers and fingers through to fine particulate dust.

Most plastics and metal enclosures offer a 4, 5 or 6 rating (objects under 1mm diameter), a 4 is suitable for a basic wiring junction protected by a wall, ceiling, cabinet or similar in a dry environment, but a 5 or 6 is the preferred option should the enclosure be exposed in any way and this covers most industrial applications where the box can be seen or is accessible as part of routine operation or maintenance.

Pressed metal enclosures offer the poorest protection and are generally a 4, cast (usually aluminium) and most polystyrene and virtually all polycarbonate enclosures fall into the 5 or 6 categories.

There is a third number that refers to impact protection, but is not often quoted; the second number is where a decision has to be made and where several clear variables come in to play: When mounting an enclosure inside a cabinet, fixing to a machine wall, a building wall or a post, the method of attachment can either maintain or instantly downgrade the IP rating of the enclosure assembly.

For example, in an industrial environment that may include water sprays, wash downs or atmospheric moisture, a screw fixed IP65 enclosure with IP68 cable glands can be rendered IP64 or lower simply by not employing grommets between the screw or bolt heads and the enclosure wall when fixing the enclosure in place.

Fixing to posts or uneven surfaces is more problematic and an external fixing of some sort such as cable-tie brackets can be very useful.

Gluing or gun applied sealant is also an option.

The lid sealing of an enclosure is the next major element to affect the sealing, basic 'click' fit lids are generally IP54 or lower.

Pressed metal enclosures are the worst, allowing either dust or moisture in reasonably easily, whereas plastic 'click' fit enclosures generally offer IP54, which provides limited protection from both dust ingress and liquids.

Cast metal enclosures or industrial plastics such as moulded polystyrene and tougher polycarbonate generally offer much higher levels of protection.

Lid fitment of IP54 and above generally requires an additional compressible seal to achieve higher protection.

Machine applied polymer seals are generally more reliable than gasket types as they are not prone to movement during fixing and a seal that runs inside the lid fixing screws is normally required for IP65 and above.

Cable entries are present in virtually all sealed enclosures offering a significant IP rating; they vary from basic cable clamps through to independently rated waterproof cable glands.

Basic cable clamps and open holes offer some protection, but where moisture is present to any degree the cable entry must offer a complete seal around the cable sheath.

Recent developments in push-fit seals have seen both the grommet type and the moulded-in version offering high ratings up to IP65 in some instances, providing protection from drips to low power water sprays and suitable for general above ground outdoor applications.

Underground use, temporary immersion, wash downs in the food and processing industries or exposure to the sea requires IP65 and above, this generally requires cable glands fixed to the enclosure wall and high quality compression seals.

An IP65 rated box is not IP65 when the cable entries do not offer the same protection.

The harmful effects of both dust and moisture to sensitive equipment, circuitry and switchgear can cause electrical shorting, component corrosion and greatly reduced reliability hence proper sealing is crucial.

Other considerations such as ambient atmospheric moisture combined with large temperature fluctuations can also cause condensation problems, in situations where this situation is likely, it always pays to fit breather valves (or grommets) to allow the enclosure humidity and pressure to equalise without compromising the intended IP rating.

Advice on specifying enclosure ratings, what is appropriate for any given application and how to avoid compromising the intended IP rating should be provided by all dedicated enclosure suppliers and specialists, in addition to carrying a range of enclosure types and accessories to provide the ideal solution no matter what the challenge.