The benefits of prefabricated wiring systems are reduced on-site labour costs, shortened construction programmes and better quality products with increased functionality. Their use also facilitates variety in design layouts and flexibility for future expansion.
Quick installation and end-user functionality are highly dependent on the prefabrication design process and the efficient ordering of components. Site management staff and installation operatives not only need to be familiar with the systems, but also aware of the potential pitfalls.
One problem with prefabricated wiring systems is their untidy appearance in the ceiling void. Also, additional materials required for adaptation or maintenance have to be sourced from the original manufacturer.
Busbar-based systems
An alternative approach to prefabricated lighting systems for lighting is the use of busbar systems. Busbars are already used to provide small power to general office areas via the floor void, but thanks to developments in light control technology they can also be used to power and control lighting circuits.
The specification of busbar technology provides long-term flexibility, as system expansion can be accommodated by plugging-in additional lighting circuits.
The main downside of a busbar installation is the relatively high capital cost, particularly with complex installations. Bends and sets in busbars add significantly to cost. For a system to be cost-effective, the building layout and other services located in the ceiling void should permit the installation of predominantly straight runs.
Both pre-fabricated wiring and busbars can also serve power requirements for other high-level services such as fan-coil units, and bems outstations. An additional advantage of prefabricated systems is that they are easier to adapt at a later date, using plug-in connectors rather than hard wiring. This feature is particularly important to facilities managers, who often need to deal with high churn rates in commercial offices.
Cost comparisons
The cost models (table 1 and table 2) compare three different wiring methods, traditional, prefabricated and busbar, providing power to lighting and ceiling mounted fan-coil units. The models are based on a standard developer's Category A general office fit-out with a net lettable area of a 28 400m².
It is assumed that luminaires are arranged in 3 m x 3 m grids using 2 x 28 W T5 lamp fittings. Lighting control is provided with a basic, non-dimmable system providing block switching, with the facility to allow an incoming tenant to incorporate localised switching or presence detectors on the lighting circuit.
The model also includes an analysis of wiring to lighting installations in other landlord's areas (stair cores and toilet blocks). Busbar systems are not included in this analysis as their installation is not practical where solid suspended ceilings and dry lined walls restrict access for testing, commissioning and modifications.
For open plan office areas, the prefabricated and busbar options are significantly cheaper (25%) to install than traditional wiring methods. Material costs of both proprietary systems are higher than for cable and conduit, and the cost savings are primarily related to the increased speed of installation.
Fast installation is achieved through the substitution of a single process for the four stages required for a conventional wiring installation (erection of trunking and conduit, drawing-in cables, final connections and testing and commissioning). On average a 75% cut in installation time can be achieved.
In the landlord's areas, which are relatively small and discontinuous, the potential labour savings of prefabricated wiring system do not offset the additional cost of fittings, and conventional installations are the most cost-effective.
The programme savings generated by proprietary wiring methods are substantial. In addition, their adoption improves the flexibility of the project programme. This enables, for example, the on-floor electrical installation to be delayed, reducing the effects of congestion on duct and pipework trades. In turn this enables the complete services installation to be erected quickly and more efficiently.
Source
Building Sustainable Design
