What’s the difference between earthing and bonding?
While they both have the same basic function – to allow fault current to flow to earth as quickly as possible, earthing and bonding do have distinct purposes. The two combined are essential for electrical safety and no electrical work should be carried out until the earthing and bonding conductors are adequate.
Earthing
Metal parts of an electrical installation can become live under fault conditions. These must therefore be earthed. This will involve the circuit protective conductor (CPC), or earth conductor, connecting the metal part of the installation to the earth terminal in the distribution board. For example, the casing of a cooker is connected via the earth conductor (CPC) back to the distribution board earth terminal which then is connected to a main earth conductor going back to the main earth terminal and to earth. In the event of a fault to the casing, there will be negligible resistance causing a large in-rush of current to flow down this conductor causing the protective device (fuse) to blow or disconnect. Thus, removing the danger.
Bonding
Bonding conductors are electrical conductors, suitably sized, depending on the size of the incoming supply cable connecting any conductive parts of a building. For example, incoming copper water or steel gas pipes and steel girders. These points are connected back to the same main earthing terminal. The bonding of these points reduces the touch voltage, if someone was for example touching our faulty cooker and a copper water pipe, the risk of electric shock is greatly reduced.
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