Figure 3.17 Simplex system

grade of PVC and the entire assembly of insulated cable within conduit is flexible. From
the installer’s drawings, the manufacturers make a kit consisting of cable already within
the conduit, cut and formed to the lengths needed on the building. The kit is delivered to
site and simply laid in position, a process which eliminates most of the ordinary site work
required for a conduit system. Although it is supplied with the cable already in the
conduit, the system is rewirable because each cable is loose in its own passage. Suitable
conduit boxes for junctions and accessories are supplied as part of the system.
There are problems which can arise with such a system. The conduit and cable are cut
to size at the factory from drawings. A slight error in setting out of the building can result
in the kits not fitting at site, with many unpleasant recriminations between designer,
supplier and installer. Discrepancies can occur even if dimensions are taken on site;
usually a typical house or room is measured and all of that type are made the same. If the
building setting out varies from one to another, some of the kits may not fit exactly and
the site electrician may have some adjustments to do. If every room has to be individually
measured, a great deal of the time-saving of the system is lost.
Another system takes the form of trunking in the shape of skirting, which is placed
around the bottom of walls in place of ordinary skirting. The system includes suitable
corner pieces and boxes to hold socket outlets and other accessories. This particular
system is very useful for buildings constructed from concrete slabs precast in moulds, but
it is still necessary to find some way of running switch drops in the wall and of taking
cables from one room to another without blocking door openings.
There are several other proprietary systems, which generally tend to be variations on
these themes, and which all have their individual advantages and disadvantages.