Cable Chaos

Hina Bhatia & Cathal McElroy find out how CABLING is all being managed

Data centre projects require huge amounts of cabling.
Data centre projects require huge amounts of cabling.

With buildings now bound with more cabling than ever, Hina Bhatia and Cathal McElroy find out how it is all being managed

In this high-powered world, cables are at the core of bringing our buildings to life. As our home, work and leisure lives become ever more electrified and digitised, the proliferation of cabling throughout our built environment has become problematic.

For those charged with designing and installing the electrical systems that keep us powered up, these issues are demanding some fresh thinking. For Ed Barrett, associate building services engineer at Atkins, the biggest design challenge with cabling and cable management is related to clashes.

“If you think of a complex project such as an airport or metro station, the amount of cabling is eye watering – and you also need to adhere to minimum separation distances. Historically all designs were drawn on paper but the use of building information modelling (BIM) nowadays makes the task less onerous. However, it still needs to be managed by skilled technicians who know what they’re looking for.”

Arvind Kumar Bhatnagar, general manager at Technical & Trading (TTE), also highlights the difficulties involved in ensuring that cabling fits in suitably with the elements of the MEP design.

“Often the wet services and other mechanical services design are not available to the electrical designer at the design stage leading to challenges later on,” he says.

Due to this lack of MEP coordination [with other mechanical services] during design, most sites need up to 40% redesign during the execution stage, leading to huge additional cost of engineering man hours for the contractor, plus delays.”

Spatial concerns are not the only issue faced by electrical system designers. Murtuza Kayam Vejlani, assistant manager of planning, design and procurement at Oasis Investment says that, when designing a cable tray system, the cable support needs to be strong enough to resist potential electromechanical forces.

“This is because during fault conditions the short circuit current that flows can produce high magnetic fields, which can interact to produce large mechanical forces,” he explains.

“These forces can cause significant displacement of the cables and therefore, by the use of cable cleats, some of the force is transferred to the cable ladder or cable tray via the cable cleat, and could be sufficient to cause damage to the ladder or tray.”

Vejlani adds that there is a need to select appropriate materials while planning any cable ladder or cable tray installation and that the choice of an appropriate corrosion resistant material and finish is always a key issue at the design stage.

“The correct choice has long-term implications and is crucial for ensuring the longevity and the aesthetics of the complete installation. For example: hot dip galvanising of cable trays and ladders is an extremely effective and economical resistant finish against corrosive environments, especially coastal or marine.”

When it comes to executing the design in the installation phase, Vejlani points out that it is important to provide 25% spare capacity when considering the actual loads that have to be supported and also the distance between the supports in order for effective distribution of weight across the entire length of the installation.

Seasonal thermal movement and/or building expansion joints (structural joints) can easily place undue stresses on the installation and the supporting structure, thus expansion couplers are a necessity to cater for this phenomena,” he says.

A specific challenge faced by electrical contractors in the Middle East is the availability of good quality cable tray accessories in the local market, according to Bhatnagar.

This means that when multiple changes occur during execution, the contractor is forced to buy local accessories for the cable tray that do not meet international standards, rather than face the long lead delivery times involved in ordering from Europe or the US that could jeopardise the construction schedule. Local manufacturers should try to fill this gap, he adds.

With the steady increase in the numbers and types of cables required in modern buildings, Vejlani also highlights the sheer amount of work required when installing cables and their support systems, and the labour challenge this poses to contractors.

“The installation of cables and their support systems is a very tedious procedure,” says Vejlani.

“Fixing of cable support systems using threaded rods requires a lot of labour and time, marking the route, fixing the support system vertically in the slab and hence installation of the cable trays and ladders. And then there should be sufficient clearance between structural slab and false ceiling levels in order to lay and pull the cables properly without damaging the exterior of these cables.”

To lessen this burden, Vejlani suggests design improvements such as dedicated routes for cables and better coordinated design of cable tray routing during the design stage itself to avoid clashing with mechanical services.

Moreover, measures can also be taken prior to installation by contractors to ensure a smooth installation process such as the redesign of cable routing as per the requirement, proper coordination with mechanical services, correct selection of materials, proper loading, and segregation of different types of cables, he explains.

Bhatnagar proposes that when designing a cable tray wiring system the designer should evaluate the National Electrical Code's (NEC) Equipment Grounding Conductor (EGC) options that are applicable for the project.

“The client’s expectations and requirements should be captured early on and coordination with other MEP services should be completed before it reaches the contractor for execution. In short, a design freeze date should be signed off before the start of the project. This way the contractor can plan to order the long lead items of better quality.”

“Moreover, the need of skilled MEP coordination draughtsmen who understand all MEP services is critical,” Bhatnagar continues. “These drawings should show, in detail, the routing of ductwork, piping, cable trays and large conduits, as well as elevation details for systems above corridor ceilings. These identify conflicts and ensure that necessary access is provided.”

For Atkins’ Barrett, the mandatory use of BIM would go a long way to mitigating cabling and cable management installation problems.

“We [at Atkins] also prefer to set different levels for different services in order to simplify the process of design and installation,” he says. “Detailed thought should also be put into longer term management and maintenance of systems – installation is only the start.”

“I would also be an advocate for prefabrication. The more technical work that can be taken away from sites the better, and there is no reason why trays cannot be prefabricated ready for insertion,” Barrett adds.

In the years ahead, Barrett foresees the focus on cabling and cable management becoming even more intent.

“The continuing advancement in communications technology and particularly increasing data transmission rates require even greater care when installing these data cables,” he says.

“One example is that to maintain the specified data transmission rate, the specified minimum cable bending radius must also be maintained at all locations along the communications raceway/pathway.

To this end, cable management systems and communications products are being designed to take into account the larger bending radii and cable diameters associated with the ever increasing data transmission rates,” he adds.

Facts:
- 25% Spare load capacity required on cable trays

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