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Making signalling power distribution systems safer
12 December 2018
In March 2012, a Network Rail contractor received an electrical shock from a signal location cabinet while carrying out routine maintenance. This incident was to have far-reaching consequences, leading to the introduction of new standards to prevent electrical exposure and specification requirements to enhance the protection and integrity of the electrical cabling using flexible conduit
This wide-ranging review involved inspecting functional supply points (FSPs) in signal location cabinets – the part connecting the cabinet to the power supply. Of the FSPs inspected, approximately 84,000 required urgent intervention to ensure they were sufficiently earthed and bonded.
One element of the remedial action was that power supply arrangements for 650V signalling distribution equipment would be changed from Class I to Class II. Today, this means that equipment and cabling casing must be non-metallic and double insulated so that if a fault develops, there can be no exposure to the electrical current. Consequently, any existing, exposed cabling used in signalling equipment applications must now be over-sheathed in accordance with the requirements.
New product specification
Network Rail created two product specifications for Class II based Signalling Power Distribution Systems – NR/L2/SIGELP/27421, covering flexible conduits, and NR/L2/SIGELP/27422, covering cable glands. These would remove the likelihood of live conductors coming into contact with exposed conductive parts forming part of switchgear assemblies and apparatus housings.
As standard, any new electric shock-proof solution should also ensure the continued and uncompromised safety, efficiency and reliability of the cabling, which is especially critical in signalling operations. Because cabling used in the UK’s rail infrastructure is subject to a wide variety of hazards – including temperature variations, UV light, water and dust ingress protection, vibration, impact and crushing – robustness and high mechanical strength is absolutely essential.
In response to this demand for improved cable protection, flexible conduit system manufacturers developed new solutions that would meet Network Rail’s exacting standards. Indeed, any product proposed for use in the UK’s rail infrastructure is stringently evaluated through the Parts and Drawing System (PADS) approval process before it can be approved for use. Each component that meets the relevant product specifications and performance requirements is then issued a unique PADS number.
Fast-forward to 2018, and Flexicon can provide PADS-approved flexible conduit systems and glands that comply with Network Rail’s relevant standards. Specifically, these solutions enable compliant maintenance and management of 650V Class II Based Signalling Power Distribution Systems in accordance with the product specifications demanded in NR/L2/SIGELP/27421 and NR/L2/SIGELP/27422.
As such, they are an ideal cable protection solution for new signalling equipment and can be retrofitted to existing installed equipment.
Yet, in addition to meeting the relevant Network Rail standards, there are other environmental concerns that inform contractors’ choice of cable protection product and manufacturer. Specifically, there was a need to ensure suitable PADS-listed cable protection solutions were available for use in flood-prone areas, or areas where cabling could potentially be immersed for long periods of time. Taking this into account, Flexicon now stands out as the only Network Rail supplier capable of providing cable protection systems for signalling and infrastructure applications that meets enhanced PADS approval.
With a minimum dielectric strength of 3.5kV in various weights, IP 68 rating and flame-retardant properties, Flexicon’s range of cable protection solutions for the rail sector are unrivalled from a technical standpoint. Ideally-suited for trackside applications, these systems offer a tensile strength up to 70kg (for 21mm) and deliver the highest levels of anti-vibration and shock-protection performance testing.