BRE DG456 PDF

Introduction

Traditional methods for providing electrical power cabling in buildings are being replaced by prefabricated products assembled under factory controlled conditions. These new products, although more expensive to buy than those used in traditional systems, enable cabling systems to be manufactured to closer tolerances and to offer greater reliability. They can also be installed more quickly or require fewer installers, or both, more than offsetting the extra cost of the hardware. Because safety features are designed into prefabricated power cabling products, safety on site will be enhanced for installers and end-users.

Installing prefabricated cabling in buildings with suitable floor or ceiling voids is a matter of assembling lengths of cabling and appliances using push-fit connectors. Stripping sheathing from cables and connecting to terminals is made unnecessary.

Figures 1 and 2 show examples of prefabricated cabling components and installation methods.

A typical circuit (Figure 1 on page 4) comprises a prefabricated master cable hub (MCH) attached to a ‘home run' cable. The home run cable is wired conventionally to the main distribution board at the building's electrical supply inlet. Prefabricated extender cables are plugged into the MCH to feed power to luminaires, air conditioning units (eg variable air volume boxes or fan coil units) and socket outlets through prefabricated ‘T' connectors, electronic control modules or additional zone cable hubs.

Cables may be laid on cable trays, fixed to ceiling drop rods or hangers using ring or cliptype attachments, or clamped directly to the soffits (Figure 2 on page 5). Cables may also be laid on floor slabs, but long runs should not be laid on ceilings.

This Digest suggests, first, the criteria for specifying prefabricated power cabling systems, and selecting manufacturers and suppliers. It then offers general guidance and procedures for installing and testing the prefabricated cabling. There is a glossary of terms used to describe power cabling systems on page 2.