ABSTRACT
The most common use of an earth electrode is for providing an earth for a TT system. A copper-plated steel rod is the most common type of earth electrode for use in a domestic installation; a steel pipe can also be used. Where an earth electrode is used for protection on a TT system, it is important that the electrode provides a low enough resistance to allow enough earth fault current to flow. The value of resistance for each circuit is known as Zs and this is made up of the resistance of Ze plus the resistance of the circuit line (R1) and circuit protective conductor (R2). With TT systems it is normal to have a high Zs value and for this reason one must use a device called a residual current device (RCD) for protection from earth faults. This device measures the amount of current that is flowing in the line conductor and the neutral conductor.
