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Legislation impacts on modular building electrical systems

An MMC modular approach is revolutionising electrical installations of modular buildings. But that doesn’t mean legislation applying to traditional buildings can be ignored.

In recent years new legislative requirements affecting electrical installations have been enacted. For example, Parts L1 and more particularly in the case of MMC, Part L2 of the Building Regulations makes specific requirements for Conservation of Fuel and Power - energy efficiency - within buildings. This is coupled with the European Energy Performance in Building Directive that must also be complied with. Now there is the 17th Edition of the Wiring Regulations that further impact on the methods by which electrical
installations are designed and commissioned.

There is no question that development in plug and play; the provision of factory assembled, type tested and waranteed distribution equipment; and a modular approach to wiring have taken MMC a further step forward. What the various new regulations impose is greater consideration of the electrical systems by
modular building designers at the earliest stage.

New edition changes the rules for MMC

Consider, for example, one of the new requirements of the 17th Edition Wiring Regulations that states cables must be at least 50mm inside a wall. Some internal walls of modular constructions would make this difficult, if not impossible to comply with. The solution is simply to install an appropriate residual current
device (RCD) for additional protection in the event of a screw or nail piercing a cable in the wiring circuit. However, this needs to be provided for in the design of the system – especially if the electrical distribution panels are also be preassembled off site.

Comparing the differing needs of, say, volumetric buildings and prefabricated buildings it is clear that most
volumetric buildings will have the wall depth capacity to comply with 17th Edition requirements. In practicality, all steel framed buildings will need far greater numbers of RCDs under the new 17th Edition requirements. Of course many buildings constructed under an MMC approach will combine volumetric fabric with prefabricated modules internally. Here, the cabling must also be considered at an early stage to ensure adequate provision in the electrical distribution and protection systems.

In many modular constructions – notably the likes of prefabricated student accommodation – there are a number of factors likely to need to be addressed under 17th Edition. Among these are the fact that mostly sockets will be less than 20 Amps; there are unlikely to be metal conduits for cables; wall thicknesses may
disallow the 50mm depth rule; and finally, the installation is unlikely to be used by “Competent or instructed
Persons” as defined by the 17th Edition. It is important therefore, that designers of such types of modular building consult experts when considering the infrastructure and the impact of legislation.

Energy is a key in MMC Part L of the Building Regulations is being revised to ensure compliance with the
legal obligations set out in the Energy Performance of Buildings Directive (EPBD). This directive, which came into force in April 2006, is a new performance standard based on a target carbon dioxide emissions rate for heating, hot water and lighting. This requires that all building owners carefully meter and monitor their energy consumption and emissions, as the owner of a building will have to make this information available to prospective tenants and buyers. Any building with a total useful floor area of more than 1000m2 must take cost effective measures to enhance energy performance and measure energy consumption. This clearly still applies if buildings are erected under modern methods of construction.

Installing energy metering technology can be carried out as part of an MMC construction by incorporating it into the main distribution panels – built and tested off site. In fact, a recent study by the Energy Savings Trust reveals that metering and monitoring energy consumption can have a relatively short payback period and a high return on investment.

Embracing MMC
Schneider Electric has applied a modular off site MMC approach that has a fundamentally different way of designing electrical schemes. The aim overall was to improve quality, safety and testing; comply easily with standards and legislative requirements; reduce the skilled labour required at first fix; reduce installation time; and reduce costs.

Essentially, a new wiring strategy uses radial circuitry rather than ring mains. This design enables better
protection of the cables and connectors joining the various outlets and increases the life of the system. It also enables a modular approach to pre-assembling equipment in the factory and then simply plugging in to the system.

Further advantages of a radial topology over the ring main are that the cable used and installation times are both reduced by 50%. Coupling this with a unique “tool free” interconnection design means that relatively unskilled installers can make the connections without jeopardising compliance with Building Regulations. By further offering cables for joining the socket outlets in various lengths, the wiring solution retains its
factory tested status giving a flexible yet compliant solution.

For the portable factory-made building market Schneider Electric has pre-built and tested incoming distribution boards, junction boxes and downstream distribution boards feeding down to both lights and pre-wired socket outlets.

A further major benefit of the new assembled standard service is that the configuration of the equipment is verified prior to building, allowing any specification errors to be identified and corrected at an early stage, before they result in inconvenience and delays. In addition, all panels and boards are fully tested prior to despatch, so users of the service can be confident that they will perform fully to specification, as well as
delivering the highest levels of safety.

To get the best from this type of installation it is important for all parties to be involved in the early stages of the project. The design facilities at Schneider Electric are staffed by specialist engineers bringing extensive experience with such integrated installation systems to bear on commercial building projects. Recent projects in the health and education sectors have shown how successful the application of MMC in electrical systems can be.

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