Steve Marr from Legrand discusses the power distribution choices that affect lighting control functionality.
While we await publication of the latest Part L Building Regulations, it seems pretty certain that they will demand much higher levels of lighting control. In reality, however, the anticipated changes are not as significant as they might first appear because, while they have not been mandatory, lighting controls in one way or another have been fairly ubiquitous in new builds and upgrades for several years.
Of course, not all environments call for an all-singing, all-dancing lighting control system, but it is important to realise that the choice of power distribution system not only dictates the level of lighting control functionality that can be installed at build; it also defines the amount of choice and flexibility that’s possible as the building’s use or occupier changes.
We can discuss the choices as four broad categories: fixed cable; lighting busbar; modular wiring or a busbar system with integrated communications bus like Legrand’s Buscom system. While any of these four systems could feasibly be installed in any environment, realistically they represent two tiers of specification, with fixed cable and lighting busbar at the lower spec, basic lighting controls end of the spectrum and modular wiring and Buscom more suited for the high end prestige office or hospitality environment.
Basic controls
A fixed wiring installation has the advantage of low material costs and straightforward installation by a skilled electrical team but the cost advantages gained in terms of outlay on materials can be outweighed by the labour intensive nature of the installation. A typical installation would require 10A circuit breakers in the distribution boards, with 1.5 or 2.5sq mm cables being fed out either as single insulated cables in distribution trunking or as twin and earth cables on steel wire cable tray.
The installation would require a relatively high number of circuits at the distribution board, with each circuit feeding four or six light fittings, and control could be incorporated with the inclusion of a simple standalone presence detector to switch each circuit. This type of installation provides no scope for intelligent, networked controls and, because it is completely fixed, any additions or changes required to the lighting control system would necessitate an expensive rewire, limiting the service life of the installation and driving up whole life costs.
A plug and play busbar installation, by comparison, may incur a higher material outlay, although those with little experience of lighting busbar may be surprised at just how small the difference actually is! It won’t come as a surprise to anyone, however, that labour time and costs are significantly reduced when using busbar.
This makes busbar a very attractive option both in terms of installed costs and in terms of fast-tracking and simplifying an installation. A typical busbar installation would require fewer but higher rated circuit breakers in the distribution board feeding 25A or 40A lighting busbars with power accessed via tap-offs that can be plugged in as needed at regular tap-off outlets. These tap-offs would usually feed an eight-way marshalling box with local fuse protection, which is connected to six light fittings. The lighting output from the marshalling box is then controlled by standalone presence detectors.
Once again, this represents a fairly simple lighting control system with limited scope for adaptability, however, unlike fixed wiring installations, there is potential for adding new lighting controls to the system and adapting the installation, giving it a greater potential lifespan.
The plug and play nature of a busbar system means that there is spare capacity on the infrastructure to put in additional lighting on the busbar or at the marshalling boxes. While a busbar installation on its own still does not provide any potential for intelligent controls or networking of the control system, it does offer an in-built flexibility that would lend itself to change of use or change of occupier, enabling the system to be adapted, albeit within the same basic specification parameters.
Higher specification
For higher specification buildings where lighting control is part of a wider portfolio of energy efficiency measures, a more sophisticated control system is to be expected, and this may also integrate with other controls as part of the BMS (Building Management System). Here, the specifier must consider the practical needs of the building and the occupier, the optimum control system for energy management and the ‘wow’ factor aligned to lighting design and functionality.
A modular wiring installation can provide the infrastructure for individual control of luminaires with intelligent, networked lighting controls that deliver a system that meets the needs of the building and/or occupier. While this type of system entails higher material costs than a traditional cabling installation, the easy-fit nature of the system keeps labour time and costs low.
A best practice approach to a modular wiring installation is to build in spare capacity at the master distribution box (MDB) and lighting control units (LCUs) to cater for future additions and adaption’s, however, as the LCUs are fixed to the fabric of the building, any subsequent changes involving the need to move or add new control units will entail significant labour costs, even though the plug and play nature of the system means that little electrical work will be needed.
A typical installation would normally involve 10 circuits grouped together in a home run that will also contain a twisted pair comms cable. The home run is prewired to an MDB at one end and supplied with tails at the other end for termination into the distribution board, with comms cable tails ready to connect to the area/floor controller of the lighting control system.
The MDB contains 10 output sockets and pre-wired flexible conduit sub-circuits plug into these to distribute power and comms. These flexible conduits then usually feed into intelligent lighting control units, each of which have nine outputs that pre-wired flexes plug into to feed individual light fittings.
A system like Legrand’s Lightrak offers such quick and simple retro-fit possibilities that it provides the ideal sustainable option for developers. At the category A stage of an office fit-out the lighting requirements of the final tenant are not known, with Lightrak, developers are able to install a cost effective lighting control solution that is adequate for the client attraction phase, but can be upgraded to meet the additional needs of the incoming tenant with a minimum level of investment in time and labour.
Offering spare capacity throughout the system, Legrand’s Lightrak provides individual control of luminaires thanks to an intelligent networked lighting control system. The system requires fewer circuits on a smaller distribution board, with 25A or 40A circuit breakers feeding the Buscom system. Fused Buscom tap-offs then feed and network pre-wired, nine-output intelligent lighting control units onto the integrated communications bus. With this installed, the Lightrak LCUs themselves simply snap-fit onto the Buscom trunking with virtually no labour and pre-wired sub-cabling plugs into the LCUs to provide power and control to each luminaire. The Lightrak system communicates via the KNX protocol and can control 1-10V, DSI or DALI luminaires, with all the control units networked together via the comms bus that is integrated in the Buscom system.
Tailored choices
As more sophisticated lighting controls become standard specification in high calibre offices and occupiers start to demand more tailored requirements, a Buscom trunking system with
fully addressable LCUs represents an excellent option for flexibility and whole life costs. As with so many other aspects of the electrical specification, the choice is subjective and should be considered in line with the building’s function and target occupiers but it always pays to understand the possibilities and limitations that are being built into the services.