FEATURE ENCLOSURES
METAL VERSUS PLASTIC L
arge, outdoor enclosures are a necessary aspect of the general
infrastructure of day to day life. Used to house vital control panels and electrical connections, these enclosures must be able to withstand all that is thrown at them to protect their contents - this includes extreme temperatures, rain, UV exposure and even vandalism attempts. On the face of it steel or stainless steel is the perfect material for outdoor enclosures. It is quite malleable, making pressed steel designs easy to manufacture and it is extremely tough with high impact resistance. In fact the majority of industries and applications can be varied and include trackside, wastewater treatment, telecoms and traffic control which have all traditionally opted for metal enclosures for this very reason.
DOWNSIDES However, there are many downsides to specifying metal enclosures. The weight of the material means that in most cases a mechanical lifting aid is required to help position the enclosure during installation, which can be extremely problematic in applications with limited access. Installation itself can also prove time consuming as the enclosure has to be earthed to meet insulation guidelines to prevent serious injury in the event of an electrical fault. It’s not just during
installation that problems can occur. Once installed the enclosure has to withstand many years of abuse from inclement weather as well as the local surroundings. While metal is extremely robust, it is still prone to denting in the event of a heavy knock. Once dented, corrosion can begin to occur which will affect the overall integrity of the enclosure - in fact a single scratch to the surface can be enough to compromise its corrosion resistance. Due to the scrap value of steel, metal
enclosures are also frequently the victim of vandalism - suffering damage which can put the enclosed electrics at risk, or even require complete replacement. Even petty vandalism, such as graffiti, can ruin
14 NOVEMBER 2014 | ELECTRICAL ENGINEERING
Due to its inherent strength, steel has traditionally been the material of choice when it comes to large outdoor enclosures - despite several shortcomings. However, can GRP offer a robust solution which offers protection where steel cannot? Here, Spelsberg answers the question
could be a sign that it is susceptible to UV exposure. Fortunately, this is an issue which can be solved through advanced manufacturing techniques available to premium GRP products.
the aesthetics of the enclosure, and is impossible to clean off without removing the protective paint layer. With all of these issues to contend with
it’s little wonder that electrical installers are looking for new alternatives. For many, glass reinforced polyester (GRP) is the solution. It offers similar levels of impact resistance to steel and boasts the same non-corrosive attributes of stainless steel at a fraction of the cost. In many other areas it even exceeds the performance of metal enclosures. For example, it is typically a third of the weight of similar sized, metal enclosures making delivery and installation far quicker and cheaper. GRP is non-
conductive and so
it doesn’t require earthing, which makes installation easier - it even lends itself to Network Rail
applications which require Class II
installation. It’s also completely resistant to corrosion, even after hard impacts and surface scratches, meaning that it is capable of providing long term, reliable protection. In addition, it is of less interest to vandals and thieves as there is no scrap value to the material. Despite these benefits there are still
many within the industry that feel that metal enclosures are the premium solution of choice. They point out that GRP can be susceptible to blooming - discolouring over prolonged exposure to UV - which
/ ELECTRICALENGINEERING
Above: used to house vital control panels and electrical connections, outdoor enclosures must be able to withstand all that is thrown at them to protect their contents
Left: Spelsberg offers a series of GRP enclosures that includes, as standard, Bloomguard
Below right: GRP offers a cheaper solution in terms of specification, installation and ongoing maintenance, while also offering high impact resistance, UV protection and electrical insulation
NEW DEVELOPMENTS Spelsberg offers a series of GRP enclosures that includes, as standard, Bloomguard which is a new development within the raw material that enables the outdoor GRP enclosure to be completely resistant to glass fibre blooming and surface erosion. It is resistant to scratching so can’t be removed, and actually makes the enclosure surface smoother which makes cleaning graffiti and stickers far easier. Metal enclosures undoubtedly do offer a
high level of impact resistance, and in the past they were the best option for maximum protection outside. However, with new advances in design and manufacturing techniques, GRP enclosures are able to offer the same degree of protection without the inherent drawback which the industry has come to accept from steel. GRP offers a cheaper solution in terms of specification, installation and ongoing maintenance while also offering high impact resistance, UV protection and complete electrical insulation.
Spelsberg
www.spelsberg.co.uk T: 01952 605 849
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