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Non-metallic enclosures are the future for trackside

06 March 2013

Samuel James Engineering supplies points heating systems for the UK rail network. Looking to prolong the lifespan of its products and maximise their safety, the company has taken the design decision to move away from metallic to more impact- and corrosion-resistant non-metallic enclosures for these arduous trackside duties.

When designing any external electrical application, one of the first design steps is to choose a suitable enclosure. Apart from the obvious considerations, such as its level of ingress protection and how it will stand up to widely varying temperatures, it is important to think about the location of the product and any possible hazards that it may encounter during its life span.

Trackside can be a very aggressive environment. Brake dust is particularly abrasive, while debris is often flung up from the track at high speeds. All Samuel James products are delivered with a 25 year life-span guaranteed, so the enclosures in which they are housed must be able to withstand these conditions. Moreover, with the proposed investment in electrification, which is coming into effect across the UK, it is also important to consider other dangers such as the electrocution hazards faced by maintenance staff.

Samuel James' points heating systems are installed at thousands of railway junctions across the UK. These comprise a control unit that monitors and maintains the optimum temperature of multiple points, together with approximately four to five smaller units, located by the track, each providing information from individual sets of points. In turn, these require further, smaller trackside enclosures to house temperature probes.

With each installation featuring ten or more trackside enclosures, a lot of time is spent considering options to guarantee that 25 year promise. This has led to a move away from the traditional metallic enclosure - prone to corrosion and denting, as well as being electrically conductive - to non-metallic alternatives. Samuel James now uses glass reinforced polyester (GRP) enclosures for trackside installations and polycarbonate (PC) housings for the temperature probes.

These enclosures are supplied under an exclusive arrangement by Spelsberg, whose heavy-duty GRP enclosures are more than a match for the trackside environment. The material offers a high level of rigidity with minimal wall thickness - thereby maximising the internal space for the electrical/electronic installation - while offering full protection against external impacts such as stone chips. Tests have subsequently confirmed the superior performance of GRP and PC compared with metal enclosures subject to this kind of impact.

GRP and PC enclosures also provide IP68 protection, are resistant to the corrosive effect of brake dust, fumes and the weather, and are electrically insulating.

The doors to these enclosures can be left or right mounted and the hinging allows door opening to up to 240 degrees for easy access. An integral drip shield directs water away from the doors in external environments and options include key locks for security and a viewing window in the door panel for easy viewing of internal components without having to open them up to the elements.

CNC machining of plastic enclosures is one of Spelsberg's specialities, and all enclosures are received fully assembled with entry points pre-drilled and fitted with hinged lids to improve access once on-site. This means that installers simply need to mount three or four terminals and the enclosures are ready for installation, significantly reducing trackside working time.

Spelsberg's GRP and PC enclosures are available in many standard sizes, which can then be quickly customised and assembled in both large and small order quantities. Entry points can be sealed with traditional IP68 dome topped cable glands or quick action grommets, which provide an IP67 in under a minute. The company also offers a range of modular enclosures which can be combined to build larger enclosures. Work is currently being undertaken by Spelsberg in conjunction with Samuel James, to develop a new enclosure for the larger main control units.

Having found that plastic enclosures provide significant benefits in terms of trackside electronics protection, Samuel James is now fully committed to investing in this technology and, in particular, to providing safe, electrically insulating products across its range.

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