HOW TO DETERMINE WHAT TYPE OF EARTH SYSTEM SHOULD BE INSTALLED
The issues to consider are shown as follows:


 

WHAT TYPE OF EARTH SYSTEM SHOULD BE INSTALLED
The issues to consider are shown as follows:

HORIZONTAL EARTH ELECTRODE
Buried about 40 to 100 cm below grade. Generally used where soil conditions are poor and there is no improvement in the soil resistivity at depth. Bed rock is near the surface and the use of deep driven earth rods is impractical. With long horizontal conductors, reactance increases as a factor of length with a consequent increase in impedance. Thus for lightning protection use a crow foot type earth.
To lower the resistance on this type of earth electrode, install with E-Mix Conductive Earthing Compound. This is a conductive material and will retain some moisture. See p8.

DEEP DRIVEN EARTH ELECTRODE
Buried conductor about 50 cm below grade and where the bed-rock is deep and allows earth rods to be driven to depths of 3 to 4 m. Generally used where soil conditions are
good and the soil resistivity at depth is better than nearer the surface. Ideal for a “ring type earth.
To lower the resistance on this type of earth electrode, install the earth rods and conductor with E-Mix Conductive Earthing Compound. This is a conductive material and will retain some moisture. See p8.

GRID EARTH ELECTRODE SYSTEM
Grids are generally required only in antenna farms or substation yards and other areas where very high fault currents are likely to flow into the earth and hazardous step
potentials may exist (see p71) or soil conditions prohibit installation of other ground systems. Grid systems, consisting of copper cables buried and earth rods forming a network of squares, are used to provide equipotential areas throughout the facility area. Such a system usually extends over the entire area. The spacing of the conductors, subject to variation according to requirements of the installation, may normally be 0.6 to 1.2 m between cables. The cables must be LECTROWELDed together at each crossover point.

STEP AND TOUCH POTENTIAL EARTH MATS
A close grid earth mat, consisting of copper cables buried about 15 cm below grade and forming a network of small squares, is used to minimise the dangerous step and touch potential voltages to safe levels for personnel. Installed in immediate area of switch rods and other areas where personnel may be exposed to ‘live’ electrical plant.
All cables must be LECTROWELDed at each cross over point. See p7 & p26.

CROW FOOT EARTH ELECTRODE SYSTEM
Good for lightning protection as radials are short and keeps impedance low. Earth rods may be attached to the ends of the radials. See p7.


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