Boxes

The use of boxes for housing switches and other accessories has already been described . The same boxes are used for conduit installations . When wiring is done by drawing cable through conduit , access must be provided into the conduit for pulling the cable in . Also where the paths of cables branch two or more conduits must be connected together . For both these reasons , a box of some conduits must be connected together . For both these reasons , a box of some sort is needed for use with conduit , and the type of box used is the same as that used for housing switches . As stated in the section on switches , boxes are available for recessing in walls , recessing within the narrow depth of plaster olny or for fixing to the surface of walls . Where a large number of conduit is to be connected to the same box , the box is made longer in oerder to accommodate them side by side .
  It can be seen in Figure 1.1 that the boxes have a number of circles on them . These are called knock-outs and their circumference is indented to about half the thickness of the parent metal . It is therefore easy for the electrician on site to knock out any one of them out in order to make a hole in the box . The hole so made is the right size to accept standard electrical conduit . It will be clear from the illustration that sufficient knock-outs are provided to make it possible to bring conduit into a box from any direction and in any position .