Dry partition

New buildings have internal partitions constructed of timber studding with light plasterboard facing , as illustrated in Figure 3.12 , or preconstructed partitioning . THis is particulrly the case with proprietary industrialized system of bulding . Such a partition has a void within it which is used for engineering services , and this is also a situation in which PVC sheathed cable without further protection is the most suitable system of wiring , provided that the cable is at least 50mm from the surface . Voids of this sort , in which PVC sheathed cable is run , are usually sufficiently accessible to make rewiring , if not easy , at least possible . Fixing of accesoris is made easy by the use of dry liner boxer as illustrated in Chapter 1 ( Figure 1.1 ) .
  It may happen that the building structure is such that PVC sheathed cable on its own is the most suitable system to use , but that there are few places where cables has to drop in plastered walls or run across floors . It is then desirable to give the cable additional protection at these places by runinning it inside conduit at these places olny . This has the additional advantage of makiing rewiring easier . As the conduit is used olny for short lengths for local protection , both light -gauge steel and PVC conduit are suitable .
  PVC sheathed cable may be buried in plaster without damage . There is , however , the possiblity that nails may be accidentally driven into the cables when pictures are being fixed to walls . Ideally , the cable should therefore be protected by conduit , but if there is not sufficient depth of plaster to make this possible it can still be given protection by shallow rigid PVC or galvanized metal channelling as shwon in Figure 3.13. many authorities feel that even this is not necessary . BS 7671 specified aeas within  a wall in which cables are installed at a depth of less than 50mm , where the cables do not need additional protection . Guidance is also given in the IEE Guidance Note .1 and the IEE On-Site Guidance . The basic rule is that cables can be run under plaster at a depth of less than 50mm without protection , in straight lines between accessories , also withint 150mm of a change of direction of the wall .
  There are situations where the appearance of an installation is of secondary importance , and where at the same time a surface system wil not receive rough usage . Such a case might occur in an old building used for commercial purposes or in simple huts at a holiday camps . PVC sheathed cable may then be run on exposed surfaces without further protection ,. Since it is visible it will not be damaged acidentally by people trying to the walls.
  PVC sheated cable is fixed with moulded plastic clips . An example is illustrated in Figure 3.14 . The clips should be spaced appropriate to the size of cables , IEE Guidance Note 1 Selection and Erection of Equipment and the IEE On-Site Guide give guidance on the spacing of cable clips .