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An introduction to electrical enclosure specification
Chris Lloyd of Spelsberg explains the basic decisions which need to be made when specifying an enclosure and how the right choice can reduce installation time and cost, and improve reliability.
Whether you're an electrical installer, design engineer or an OEM, the chances are that you deal with electrical enclosures on a day-to-day basis. While on the face of it the humble enclosure may seem to be one of the simplest components to specify, in reality the variety of choice available on the market may mean that the most obvious solution isn't always the best in terms of reliability and long term profitability.
To many end-users an enclosure is simply a box in which to store electrical components or connections, and the specification process needs to take no more time than is required to decide on the right size. However, if you look at the range of options on the market it becomes apparent that there are many more variables to take into consideration. Spelsberg alone has over 4,000 standard products and each one of them has been designed with a unique set of requirements in mind.
Enclosures are available in many different materials, shapes and sizes and all of them are relevant to different sectors of the market. The suitability of each enclosure depends on the application that it will be used for. Some may need to provide protection from external knocks; some may need to provide suitable external mounting options; and some may need to offer quick installation to keep on-site labour costs low. By understanding how the different options affect performance the end-user can avoid making an unsuitable selection which could cost them in the future.
Enclosure material is the first, and probably most fundamental, choice to be made. The two basic choices are plastic vs. metal but in reality the two groups can be broken down further: eg. polycarbonate, ABS, polystyrene, glass reinforced polyester (GRP), aluminium, steel, and even cast iron. For the majority of modern applications plastic construction is the favourable choice as it's typically lighter, less expensive and easier to include built-in internal mounting options for quick installation. However metal enclosures are useful for applications which require protection from potentially heavy external knocks, such as building sites, mining and quarrying. Though in these instances GRP may be considered superior as metal enclosures are prone to corrosion once dented.
Simple rules for plasticsDespite the wide selection of choice between different plastics there are typically a few easy to follow rules. Polystyrene and ABS enclosures offer a lower tensile strength and less UV protection but the costs are low which make them ideal for applications which are inside and may require a lot of units at a lower cost. Polycarbonate offers increased tensile strength and is UV resistant which makes it ideal for harsh applications and outside installations.
Having chosen the correct material for your application it's also important to consider the internal designs of the enclosure and how they meet with your requirements. The most obvious consideration is the size. Both the external and internal dimensions should be considered as some enclosures will make better use of the space inside for housing your component. Sourcing an enclosure with the correct dimensions can ultimately make installation easier and less time consuming while also ensuring that the external aesthetics are optimised.
Due to the variety of components which may be housed within an enclosure, most good manufacturers offer a plethora of different internal mounting options to further simplify installation. When you're specifying an enclosure you should consider what will be housed within it and ask what mounting options are available. Typical examples are PCB or terminal mountings, DIN Rails or separate compartments for housing batteries.
Some applications are even more specialised and many of the enclosures that Spelsberg and other manufacturers produce reflect this in their designs. The most obvious example is the AK range of distribution enclosures which are designed to house components such as Miniature Circuit Breakers (MCBs) on a DIN rail with a transparent window which can be easily opened for access to the components. Other examples of application specific enclosures from Spelsberg include: the IBT and IBTronic junction box range for pre-cast concrete construction; WKe range of fire resistance enclosures with up to E90 protection; and PV enclosures for photovoltaic installations.
Of course with over 4,000 possible selections it's impossible to cover all of the possibilities here. Equally it is unrealistic to expect end-users to keep up to date on all the product developments within our industry. This is why most good enclosure suppliers, such as Spelsberg, employ sales engineers who have experience in the industry and are able to offer specification guidance based on your unique design. However, by understanding the basic requirements of your application you can ensure that the enclosure you choose offers all the protection and performance that will be required.
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