Circular boxes

In addition to rectangular boxs of the sort illustrated , circular boxes are also made . These are useful for general conduit work and terminating wiring at points which are to take fittings .
  When boxes are used for connecting lengths of conduit rather than for housing other accessories , they must have the open side covered with a blank plate . A typical plate is shown in Figure 1,9 , Circular plates are also made for circular boxes . It should perhaps not need saying that when a box is recessed in a wall , the cover must be left flush with the surface of the wall so that it can be removed to give access to the cables inside the box . This is particularly important if the system is installed with the intention that it should be possible to rewire or add cables later .

  Boxes have a wiring terminal which enables a cable to be connected to the metal of the box. This is used for connecting a circuit protective conductor ., The purpose and use of earthing is discussed in Chapter 9 . The important of the earth terminal on the box arises when the accessory which is housed in the box has to be earthed through the box . AThis is particularly important when a plastic conduit system is used which necessitates the use of a separate circuit protective conductor . These must then be some means of connecting the circuit protective conductor to the accessory and this can become difficult i there is no suiotable terminal in the box for making the connection . it is also recommended that an accessory requiring earthing , installed on a metallic conduit installation , is provided with a lead between the earth terminal on the box and the accessory , if the box has adjustable tags such as on some knockout boxes .