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Metal versus plastic for large outdoor enclosures

Metal versus plastic for large outdoor enclosures

Used to house vital control panels and electrical connections, large outdoor enclosures must be able to withstand all that is thrown at them - extreme temperatures, rain, UV exposure and even vandalism attempts. Steel has long been the material of choice despite several shortcomings; but can GRP offer a robust solution which offers protection where steel cannot?


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 - including trackside, wastewater treatment, telecoms and traffic control - have traditionally opted for metal enclosures for this very reason.

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 requiring complete replacement. Even petty vandalism such as graffiti can ruin the aesthetics of the enclosure, and is impossible to clean off without removing the protective paint layer.

Turning to GRP

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 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 who 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 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.

Spelsberg offers a premium series of GRP enclosures that includes as standard 'Bloomguard'. This 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 off 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 on-going maintenance while also offering high impact resistance, UV protection and complete electrical insulation.
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