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INTRODUCTION

The electrical connection of a part of the lightning rod or of an electrical circuit with the earth is made with an earth termination system.

A earth termination is formed by electrodes and other subterranean elements, whose objective is to lead the currents produced by lightning discharges or from industrial generation to ground.

TYPES OF EARTH TERMINATIONS

There are two methods for the construction of earth termination systems, where the most used one is that of profundity (javelins, active electrodes, plates or similar, etc.). For certain cases the surface method may be more appropiate.

PROFUNDITY:

JAVELIN: It is the method most used for earth termination systems due to its easy installation. The earth electrode is firmly set into the ground.

It is formed by three javelins with minimum length of 1,5 m, vertically set in the ground forming a delta with sides of equal length. These are connected with unshielded subterranean cable or copper bands in a trench in 60 a 80 cm. depth, and it is connected to the network of earth electrodes through the test points in the registering case.

The distance between the different picks is equal to the double length of the picks: D=2xL (length of the picks).

PLATES AND SIMILAR: They are less used since a pool has to be excavated. The method is used when with other methods insufficient values are obtained and in sites with very reduced surface to put the picks.

Normally a pool with 2m depth is made and the plate is installed. vertically. It is filled with earth where other substances are added to reduce the resistivity.

SURFACE:

GOOSE FOOT: This method for earth termination construction is used on rocky soils or grounds with difficult excavation.

It is formed by 25m of copper band or cable divided in three subterranean branches in trenches with minimum depth of 60 cm, where the angel between the branches is 45º.

EQUIPOTENTIALITY OF THE EARTH TERMINATIONS:

If the building to be protected has an earth termination system for grounding of the electrical installation, then the earth electrodes of the lightning rod installation are connected within each other.

D: down-conductor of the lightning rod

B: earth circuit located on the bottom of the building excavation

P: earth electrode of the lightning rod

This connection is made on the level of the ground at the earth electrode. If this connection is not possible, then the interconnection is made on the earth plate. In this case the trajectory of the unifying conductor must be made such as to avoid a possible induction on the cables and material located in the proximities.

In any case the interconnection has to be made with a device which allows the disconnection in order to later carry out controls concerning the resistivity.

 
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