Materials used in earthing systems must be able to:
When lightning or a fault current enters the ground, the resulting voltage spreads through the soil, radiating outward from the point of entry. The further the distance from this point, the lower the voltage present—much like ripples in a pond diminishing as they move away from where a stone was dropped.
This phenomenon is important because current passing through the heart can cause fibrillation, which may be fatal.
To reduce dangerous potential differences, equipotential grids can be installed to equalise voltage levels across an area. Additionally, it is good practice to bury conductors and earth rods at least 1 m below ground level, covering them with a thick layer of insulating material such as rock.
1. Simple Earth Electrode
This can be a driven Earth Rod, an Earth Plate, a Mat or a length of buried conductor – or a combination of both.
2. Crows Foot Electrode
Can incorporate Earth Rods – the rods would be spaced at least twice their driven length apart.
3. Counterpoise Conductor
Can incorporate Earth Rods – the rods would be spaced at least twice their driven length apart.
4. Grid Conductor
Can incorporate Earth Rods – the rods would be spaced at least twice their driven length apart. For example, in a sub-station or cell site.
5. Earth Plates/Mats
For example, for protection of an operator at switch positions.
The choice of Earth Termination layout design depends on multiple factors, but essentially . .
The purpose
The ground conditions
For Lightning Protection, BS:EN 62305:3 advocates two types of Earthing System:
The soil composition also affects the resistivity of the soil itself. The presence of salts can significantly reduce resistivity which also, with some other elements, can become extremely corrosive to the material used in an earthing system.
Corrosion resistance is of paramount importance.Soil resistivity readings should be taken prior to designing an Earth Termination Network. The reason for this is that the nature of the soil has a major influence over the final resistivity of the Earth Termination network.This can be illustrated in the following tables . . .
Achieving the desired earth electrode resistance is not always possible, particularly in areas with unfavourable ground conditions such as hard rocky terrain, mountain tops, or dry soils.
In regions with high soil resistivity, Greenwire provides a range of conductive aggregate solutions to improve resistance levels.
We recommend copper earth electrode systems for their naturally low resistivity and excellent corrosion resistance. Our product range includes:
Solid copper earth electrodes and conductors
Solid stainless steel electrodes
Copperbond (copper-coated steel) electrodes and conductors
Copper conductors
Earth bars and bonds
Exothermic welding systems
Greenwire does not recommend the use of bare mild steel in buried earth termination networks due to:
Higher resistivity compared to copper
Poor corrosion resistance compared with solid copper or copperbonded steel
All earth connection components must be corrosion-resistant and capable of carrying the required fault current rating of the associated conductor.
It is essential that all Earth Terminations are capable of carrying the current specified in the earthing design.
This requirement applies not only to the conductor itself but also to the connectors used within the Earth Termination network. Exothermic joints carry 100% of the conductor’s fault rating, whereas bolted, braided, and crimped connections do not. With this in mind, Greenwire offers a complete range of exothermic welding equipment.
Exothermic welds enable the finished joint to carry the full fault rating of the connected conductors. They never loosen over time and, being composed primarily of copper, offer outstanding corrosion resistance.
The Greenwire exothermic joint provides:
Full fault current carrying capacity
Excellent corrosion resistance
Simple and reliable installation
However please note, there are instances where a bolted connection is required. For example, where the earth conductor needs to be disconnected from the earth electrode for testing, or where the installation of an exothermic weld is not possible.
A chain is only as good as its weakest link . . . poor component selection can seriously impair a system!
