All of the individual earth conductors of the various circuits in your house are connected to one heavy cable in the consumer unit. This cable is sheathed in green, or in green and yellow, and it runs from your consumer unit to the consumer's earth terminal, which looks like a hexagonal bolt situated below the unit. In most houses in towns and cities, the earth cable continues from the earth terminal to a clamp on a metal sheath of the main service cable, just below the sealing chamber. Until recently, most electrical installations were
earthed to the cold water supply. This meant that the earth leakage current passed along the metal water pipes into the ground in which they were buried. However, with more and more water systems being replaced by non-metallic, non-conductive pipes, this type of earthing is no longer reliable.
You will find that your pipework is connected to the earth terminal just in case one of the live conductors in the house touches a pipe at some point. The same earth cable is usually clamped to a nearby gas pipe on the householder's side of the meter before running to the consumer's earth terminal. This means that both the water and gas pipes are cross-bonded so that the earth leakage current passing through either of them will run without being hindered on to the clamp on the cable service sheath and so to the earth. These clamps should never, under any circumstances, be interfered with or removed.
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