Re: Types of Earthing (as per IEC Standards)

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Points to consider in BS 7671 regulations

  • Earth electrodes

    BS 7671 lists a wide range of earth electrodes recognised by wiring regulations, including earth rods, earth plates and underground structural metalwork. The single most importance deciding factor in which type of electrode to use is resistance capacity of the soil in the ground. Ideally it should virgin, undisturbed ground, and the effects of soil drying, freezing, and the potential for corrosion, should also be considered, with tests carried out in the worst weather conditions.

  • Sizing of Circuit Protective Conductors

    Several factors must be considered when working out the required size of circuit protective conductor. A minimum cross–sectional area of 2.5mm2 copper is necessary for any separate circuit protective conductor, meaning one which is not part of a cable or created by/contained inside a wiring enclosure.

  • Earthing Conductors

    Earthing conductors defined by BS 7671 as a protective conductor connecting the main earthing terminal of an installation to an earth electrode must be sized appropriately, especially if partially buried. They must be made from suitable material and protected against corrosion and mechanical damage. The appropriate size is determined in the same way as for a circuit protective conductor, except for with buried earthing conductors, in which case check BS 7671 for further guidelines. In addition, earthing conductors for a TN–C–S supply should not be smaller than the main bonding conductors.

  • Special Locations

    These are locations where extra precautions need to be taken. For example PMEs cannot be used for caravans or boats as the combined neutral and protective conductor is not allowed to be connected electrically to any metalwork in them, whilst a TT system is recommended for hazardous areas such as petrol stations, and should be accompanied by the supply of a separate electrode and circuit breaker such as an RCD, in order to ensure that the earthing in the petrol filling area and the PMP earth of the distribution network are separated.

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