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A box is a box? Think again!01 July 2007When specifying an enclosure there is rather more to consider than you might at first think. We asked the experts at Rittal to spell out the dos and dont'sThe term industrial enclosure applies to the physical structure that contains the electrical equipment or circuitry and should provide support for all the internal components as well as isolating the interior from any dangers or containments that may be present in its surrounding. The constant changes within industry have driven the design and development of enclosures to new levels and successful manufacturers have had to stay ahead to meet the constant demands placed on them. In today’s environment, when considering which enclosure is suitable for an application, the basic enclosure is only the starting point.
Enclosures were first produced in very basic shapes with squared off edges, doors and glued-on foam seals. Built mainly from carbon sheet steel they were constructed from single pressed parts, a frame with U shaped folded profiles for strength and bolted together. Modern enclosure manufacturing takes place in fully automated assembly halls, with robot welding machines and automatic processes that produce, pack, palletise and warehouse the products. Today, cabinets can now be heat, chemical or UV resistant; they can offer protection against water, dust and even be explosion proof. The enclosure industry is now the second biggest user of steel after the car industry.
Electronic systems perform at their best when they are protected, especially in severe or hostile environments. In fact, the more benign the environment, generally the better the performance and the greater the life expectancy of the enclosure. If an enclosure is housed in an air-conditioned room, with controlled temperature and humidity and no likelihood of shock or vibration, it can be expected to provide a long and reliable service for many years. However, if exactly the same enclosure was placed in an industrial or hostile environment the performance and life expectancy would plummet as the enclosure has not been properly specified to suit that particular environment.
Enclosures to protect against the ingress of moisture and dust will need to be specified differently to those that are just destined for general use. IP ratings should be carefully considered as over-specification can result in unnecessary expense. Typically, the more hostile the environment the enclosure is to be situated in, the higher the IP rating. For internal use and, in particular, indoor locations where there is little dust and no likelihood of the enclosure being washed down, the IP rating could be as low as IP43. It is paramount to choose the right IP rating for the environment as the choice between an IP43 or an IP69K protection category can make the difference between the success and failure of an enclosure to meet its specified requirements.
In harsh environments, particularly if the enclosure is to be subjected to rigorous wash down procedures, the internal electrical equipment will need to be protected against any form of water ingress. In these situations it is recommended that a sealed enclosure be used which meets the demanding standards of IP69K, currently the highest protection standard available against high-pressure hosed water penetration.
When mounting an enclosure or fixing to a machine wall, the method of attachment also needs to be considered as this can either maintain or instantly downgrade the IP rating. In an industrial environment that uses water sprays, washdowns or has atmospheric moisture, a screw fixed IP69K enclosure with IP68 cable glands can be rendered IP64 or lower by simply not employing the correct grommets between the screw bolt heads and the enclosure.
Manufacturers, such as Rittal offer a wide range of IP69K enclosures in stainless steel which are specifically designed for use where high-pressure wash downs are required. These enclosures are also suitable for outdoor locations, but there are also other considerations to be taken into account when an enclosure is to be situated in an outdoor environment - particularly temperature fluctuations, which an IP69K wash-down cabinet is not designed to protect against.
Temperature fluctuations can have a severe detrimental effect on the internal components of the enclosure as they can cause the enclosure to act as an oven in summer or a freezer in winter. To overcome these wide variations, the enclosure may need to be double-skinned, insulated and include both heating and cooling systems to maintain optimum performance conditions. (In the UK it is necessary to allow for a variation between -27.2ºC and + 38.5ºC as these are actual recorded temperatures, and this doesn’t account for ‘solar gain’ – the cumulative heating of a sealed enclosure - or the ‘chill factor’ associated with winds of 123 to 150 knots). Apart from temperature variations creating a possible need for enclosure heating, there is also the likelihood of condensation forming when the temperature plummets, which will also require a heater to minimise the effect.
Further requirements for enclosures located outdoors include resistance to vandalism and graffiti, and even the ability to withstand impact. Not only will they need to be of rugged metalwork, which in roadside cases may need to withstand vehicles that unexpectedly leave the road, but the joins between the door and sides or top must be resistant to levers being inserted to try to prise the cabinet apart, and the locks should be burst proof and secure.
Standard grade 304 sheet steel enclosures are easy to work and are suitable for outdoor industrial sites such as a food/diary processing plant or a chemical or pharmaceutical plant as they offer protection against corrosion. However, more aggressive environments, such as those near the coast or in a maritime environment, should consider grade 306 as this offers a higher corrosion resistance. Corrosion resistance can also be significantly improved with the application of a ‘nano-technology’ coating. Containing high-density nano-particles, these nano-coatings form an ultra-thin, glass-like surface, which is not only highly durable but also provides a barrier against corrosive influences.
Under the ATEX directive, the requirements placed on enclosures for use in explosive environments is very high. Enclosures that meet the ATEX100a certification are imperative where explosions are possible as they are designed to contain the explosion if an electrical device ignites any flammable substance within the cabinet. Rittal offers a range of empty enclosures, which all meet these strict demands.
EMC (electromagnetic compatibility) shielding is also a necessity in certain environments, as electromagnetic protection is needed to protect sensitive electronic equipment from interference generated by neighbouring devices. EMC shielding ensures that any electromagnetic radiation entering an enclosure is greatly attenuated. It also works in reverse: electromagnetic radiation from equipment inside an enclosure is contained within it. An enclosure with opening doors or panels can present problems. Electromagnetic compatibility can be improved by using an enclosure with special seal arrangements and contact clamps that guarantee continuity of shielding between the enclosure and its mating parts.
Reputations are built on expectations and trust. Anyone within the enclosure market can offer a unit that provides the minimum required, but to what extent the equipment is ‘fit for purpose’ should be a key issue in the choice of a supplier. Attention to detail and high levels of quality are prerequisites, but look also for expertise in design and integration of systems enclosures for use in many different environments. If your supplier meets these criteria, then you are well on the way to a successful installation.
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