Standard practice

Standardised, pre-wired systems move the burden of manufacture from messy site conditions to a controlled factory environment, often using automated manufacturing techniques. The influential Rethinking construction report by the Egan Taskforce identified standardisation and prefabrication as one of the prime movers in the drive to bring about better value for clients, better quality and better productivity, but working practices rarely change overnight and there are obstacles to overcome.

To help disseminate the benefits of the pre-wired approach, the DETR has commissioned the Building Research Establishment (BRE) to undertake the project "Overcoming the barriers to standardised wiring systems". In late January, the BRE held a workshop in conjunction with the Electrical Contractors' Association to bring contractors up to speed on the benefits of standardised wiring systems, highlighting case study buildings, including the BRE's own Environmental Building.

"The problems associated with the installation of conventional wiring systems can be solved to a large extent by shifting the manufacturing burden off site and integrating the wiring systems," says Liam Roche of the BRE's Environmental Engineering Centre. This can be achieved with the replacement of the standard components of conventional systems by modular, prefabricated, integrated alternatives. Trunking and conduit can often be avoided entirely by the use of integrated armoured cabling containing shielded wires for a number of neworks as well as for power.

The difficulties associated with the installation of conventional wiring are mostly avoided, reducing the need for specialised skills on site. "The installation of prefabricated wiring systems is to a large extent 'plug and play'," says Roche. "The connectors used generally prevent incorrect connection of wires."

Lighting equipment manufacturers can produce batches of luminaires with compatible connectors for a modular wiring system, and similar connectors can be produced for fixed devices and even socket outlets, greatly speeding up installation.

Benefits and barriers

Modular wiring may cost more upfront, but reduced labour costs quickly tip the balance in its favour. "The typical project savings from using modular wiring for power, over a conventional wiring system, have been estimated at 25-50%," says Roche. "This results from a 30% increase in component costs coupled with a 50-70% reduction in labour costs. Because the installation process is so straightforward, programme reduction is typically from 70-90%, which increases the cost effectiveness further."

Probably the biggest barrier to the uptake of standardised wiring systems is the inertia of established practice. The electrical contracting industry is slow to change and may well remain so as long as there is a lack of information, uncertainty about long-term performance and the availability of replacement components.

"The central aim of the BRE project is to find ways to address these barriers," explains Roche. "It is clear that some of the most important barriers are about lack of information and uncertainty, rather than clear disadvantages."

This will change as workshops such as the BRE/ECA initiative start to spread the word. Ian Townsend of Modular Wiring Systems Europe outlined his company's concept for distribution of sub circuits, something that was originally developed in the USA for lighting applications. Modular Wiring's components simply plug together and are supplied as a system based on three main items: a master distribution box, a lighting/power 'T' and extender cable.

The master distribution box eliminates header trunking and comes pre-wired for up to nine circuits. Extender cables, which eliminate conduit, are supplied in standard lengths and come in lighting and power variants. Lighting/power Ts come factory-fitted to equipment and eliminate on-site connections.

M&E contractor Matthew Hall found out the benefits of the modular approach on the refurbishment of 99 Bishopsgate in London's square mile. The 27-storey office building underwent rapid refurbishment following bomb damage and the project called for fast track prefabrication methods. Modular Wiring was chosen for the lighting and power circuits, with all conduit, trunking and cable trays eliminated.

"Traditional estimates of 675 days were reduced to 81, and overall savings were in the order of 40%," says Townsend.

Townsend sees benefits for everyone in the construction chain. The construction manager has a ready-made programme accelerator, avoids clashes between trades, limits traffic between floors and concentrates labour and materials to set areas. The m&e contractor minimises labour requirements, uses the minimum number of components in what is a second-fix operation, decreases on-site storage and reduces snagging/testing.

Marshall-Tufflex is another company offering cable management solutions which are quick and easy to install. Its Specialised Applications Division offers pre-wired units designed to overcome on-site installation problems, particularly in fast track installations. By doing the bulk of the work off site, installation time can be dramatically reduced, particularly in office and hotel applications where there is a great deal of repetitive wiring.

One recent application of Marshall Tufflex's Sterling Busbar system saw the product adapted so that it could be installed vertically as preassembled sections in the form of wall-mounted powerpoles. "The location of existing central heating radiators made it too difficult to install trunking at dado height around the perimeter," explains Stuart Mann, Technical Products Manager for Marshall Tufflex. "By preassembling 2·5 m lengths of pvc-u Sterling with the busbar assembly, mcb housing and the required number of socket outlets, these purpose-built units were able to overcome a major installation problem within a very tight time frame. So that the outlets could be mounted the correct way around on the vertical sections, we engineered a special version of the Sterling single gang flush-mounted accessory." Once on site these bespoke units proved easy to install, as all the contractor had to do was connect up the power services and run IT and data cable through the outer compartments.

Contractors on these and other projects will need no convincing of the benefits of the prefabricated approach. With the BRE/ECA initiative increasing awareness and confidence among contractors, Roche is certain that standard solutions will become standard practice.

"When barriers are overcome by better availability of information, long term experience and the introduction of appropriate standards, it is likely that the use of modular, prefabricated, integrated wiring systems will become the norm rather than the exception." If we are truly to, in the words of Egan, "Rethink construction", then let's hope Roche is right.