Matt Crunden from Legrand’s cable management business discusses the different types of cable management that specifiers can choose from and the considerations that should be taken into account when selecting a ‘best fit’ system for the installation
While it is usually hidden from view and often the unsung hero of the electrical installation, cable management is generally a subject that causes much debate amongst consultants and contractors.
Though the consultant will probably specify the cable management type it is the contractor that installs it…..and the priorities of these two project delivery partners are often quite different. Whereas the consultant is clearly focused on specifying a robust cable management solution that fits the design, location and energy loading requirements of the building, the contractor will, in addition to these factors, be keen to minimise costs, time on site and the number of suppliers they need to deal with on the scheme. The one thing that both consultants and contractors tend to have in common, however, is that they like to work with a cable management system that they know, which can often means that what’s specified often has more to do with past experience than a clear process of selection.
Experience can be a valuable asset in the specification process but it can sometimes lead to over-specification of the cable management or mean that an appropriate system is overlooked. There is no such thing as a typical installation but it is possible to discuss cable management specification in the context of generic building types, locations and challenges to determine how best to specify the optimum system at minimum installed or whole life cost.
Location, location, location
Perhaps the first question to ask when specifying cable management is whether the system is required to protect cables or to support them. A distribution trunking system, such as Legrand’s Salamandre IP4X range will be required to protect single insulated (non-sheathed) cables within a completely enclosed cable management system and this high level of protection also makes trunking the ideal solution for tamper-proofing essential supplies. The complexities of selecting between cable ladder, cable tray and steel wire cable tray can be much more subtle and subjective.
One of the basic determining factors is the location of the installation and the location of the cable management within that structure. Where the building is exposed to corrosive or marine environments, such as offshore rigs, coastal locations, chemicals plants or transport infrastructure, specification of a deep galvanised or stainless steel cable management system may be advisable. For example, Legrand’s Cablofil steel wire cable tray in 316L stainless steel was chosen as the cable management system for the £51 million re-build of Weston Super Mare’s Grand Pier. Cables carrying power to the sea end of the pier were installed underneath the external pier structure where the waves would lap at the cable management so the contractor chose to use 200mm marine grade Cablofil steel wire tray with lidded enclosures, which was pre-coated with an anti-corrosive treatment prior to installation.
It’s not just coastal locations that may require stainless steel cable management or special finishes; any cable management system that is installed externally will need to be hardwearing enough to withstand rain, ice, snow and exposure to U/V. In industrial settings it may also need to be resistant to corrosive elements such as halogens. Often, cable ladder is the default choice in these environments as it is very robust, however, cable tray can be a suitable and more economical option and may even provide greater protection to the cables, particularly when used with a lid.
A weighty question
While in simple terms the load bearing capabilities of open cable management systems generally decrease as the systems become more lightweight, the real picture is more complicated. There is significant overlap in terms of load bearing between different types of cable management systems and between different proprietary brands and, in many cases, two or even three of the generic system types may be suitable for an installation.
The question of weight should not be considered in terms of load bearing alone, however, but also in terms of any ancillary loading applied to the cable management system and in relation to the weight of the system itself. The weight/strength ratio of the system will have a direct impact on the viable span between fixings and where optimum spans are desirable steel wire cable tray is often the best option. Hanging weight, meanwhile, calls for greater tensile strength, and cable tray or cable ladder may be more suitable.
The required bending radius for the cable that needs to be accommodated should also be factored into the specification decision and product width is a key factor in this regard, with steel wire cable trays usually available in widths ranging between 50mm – 600mm, perforated steel cable trays in 50mm – 900mm widths, and cable ladders in widths of between 150mm – 1200mm. While cable ladder fittings are generally available in 300mm radius as standard, they are also often available in 450mm, 600mm, 750mm, 900mm and even 1200mm radii to accept any cables, including Steel Wire Armoured (SWA) cables with large bending radii. Conversely, perforated steel cable trays usually have a much smaller radius and cannot accommodate cables with larger bending radii and, while steel wire cable trays can be configured on site to enable large radii, the size and weight of the cable itself will determine whether or not this is a viable option.
Any cable management specification should take into account practical considerations for the end user and, in that respect, factoring the building’s purpose into the decision making process is critical. In the data centre sector, for example, where the ambient temperature must be kept constant to safeguard delicate electronic equipment, optimised natural ventilation of the cables is essential, so it’s advisable to choose a suitable cable management system which offers the most ‘free air’, such a steel wire tray. However, in an office environment, all cable management systems provide sufficient ventilation for normal requirements: the perforations in steel cable tray ensure cables are ventilated even in a lidded installation and for distribution trunking installations there is a strict 60% air to 40% cables ratio that ensures sufficient ventilation for the cables.
Because specification of the right cable management system for many types of installation is so subjective, often a significant element of the decision comes down to cost. In simple terms, the more steel required to manufacture a cable management system, the more expensive that system generally is. However, assessing the cost of an installation is far from simple. A host of other factors should be considered including labour, future proofing, recyclability, waste and longevity to assess costs on an installed and whole life basis.
While steel wire cable tray tends to be less expensive than cable tray or distribution trunking, there is often more wastage as the product is cut and shaped on site rather than being custom ordered to fit. As BIM (Building Information Modelling) software becomes more widely used as a specification tool, procurement will become more exact and it will be interesting to see how this affects the cost comparison of generic cable management types. In the meantime, the best advice to specifiers is to select a system that combines faster fit accessories with the flexibility to adapt should an ins
tallation need to be reconfigured in the future because labour is the biggest cost in any installation and a future proofed system completed within a minimised time frame is top of the client’s wish list.
There may not be any definitive right answers for many cable management installations, but specifying the most appropriate system is all about asking the right questions. By working with a supplier that can offer honest, expert advice across a wide range of systems, specifiers can ensure that their decision making process is as objective as possible.