Modern Building Services

MODERN BUILDING SERVICES MAY 2023 27 FEATURE ELECTRICAL SERVICES Due to the risk of corrosion, steel trunking, conduit and cable trays are not suitable for areas with limited weather protection or with high levels of moisture. Although aluminium is generally more resistant to moisture due to its naturally occurring aluminium oxide coating, it can still corrode. For example, when in contact with other metals through a process of ‘galvanic corrosion’ or in acidic or alkaline environments that will strip it of its natural protective layer. Similarly, PVC-U can adversely react with certain chemicals, which may damage the material. Glass Reinforced Polyester (GRP) provides an alternative that is suitable for these environments. GRP does not corrode, can withstand contact with many common chemicals, including acidic compounds, and is UV and temperature resistant. As such, GRP cable management products are used widely in the rail, road and marine sectors as well as within petrochemical and industrial process facilities. GRP tray, ladder and trough systems are also highly suitable for more general applications such as cable management in external spaces and outdoor storage areas. It is also ideal for use in leisure facilities such as swimming pools, where solutions must cope with humidity and long-term exposure to airborne compounds. Fire performance A factor that has gained increased importance in recent years is the issue of fire performance. Selecting non-fire-propagating products with low emission properties has never been more important. PVC-U as a material is resistant to ignition and is self-extinguishing so it does not contribute to the spread of fire. Similarly, aluminium, steel and GRP are all classified as low smoke zero halogen (LS0H) materials. In addition, the 18th Edition of the Wiring Regulations also includes enhanced regulations around fire safety. In the event of a fire, falling and fallen cables can present a serious hazard to those evacuating as well as firefighters moving into and through the building. Regulation 521.10.202 of the Wiring Regulations requires that all cables be adequately supported using non-combustible fixings to prevent premature collapse in the event of a fire. This means that the cables have to be fixed to the fabric of the building using metal clips and supports that have a melting point high enough to sufficiently withstand the heat of a fire – 1000°C for up to 120 minutes. In effect, materials such as plastic and aluminium are no longer acceptable as a sole form of support. Where PVC-U or aluminium trunking or trays are used, fire-resistant cable clips must be fixed to the wall (within the trunking) or the ceiling. Some organisations are aiming for a higher level of fire safety and as a result are specifying steel systems due to the higher melting point of between 1200 and 1500°C, depending on the composition. Providing the steel cable management systems are connected to a fire-resistant element of the building’s fabric, then it can effectively protect from the risk of fallen cables. Installation factors In addition, there are some situations where the requirements of the building can be met while improving the speed or simplicity of installation. This is often important where project timeframes are under pressure or if installation has to be completed with minimal disruption to occupants. Flexible conduit is typically simpler and quicker to install. However, many products do not meet all the technical or functional requirements. The need for physical or electromagnetic cable protection means that galvanised steel is often selected. Multi-layer conduit, such as MT Supertube that comprises polyethylene internal and external layers over a continuous aluminium tube, provides flexibility, mechanical strength and EMI shielding when metal fittings are used. This type of conduit can be fitted easily without the need for specialist equipment and can be supplied in coils of up to 100 metres, meaning fewer fittings and minimal waste. This simplicity can also reduce labour costs. When choosing a cable management system, there is no one-size-fits-all solution, and many factors must be considered. A leading supplier, that can also offer a full range of systems, will be able to provide guidance on the best option for a given application to ensure all requirements are met. More information can be found at www.marshall-tufflex.com