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Earth rods

Discover our earth rods, their characteristics and specificities, the means of connection to your earthing network

Ground connections and soil's resistivity

The importance of grounding and soil resistivity

Understanding the importance of ground connection and resistivity of soils

Earth rods are essential elements in the realization of durable, low-resistance (underground) grounding systems. Their main advantage over other types of grounding electrodes such as grounding grids or buried conductors is that they allow to reach the deep layers of the ground, which are often more conductive than the surface layers. As a reminder, the resistance of an earth electrode depends essentially on :

  • It's dimension
  • It's shape
  • It's soil's resistivity in which it is established

This varies according to the nature of the soil, but also the humidity level and the temperature (which varies according to the season). And if the soil is not homogeneous, it can also vary according to the depth. For example, the geological layers of the subsoil through which water flows are not suitable for the establishment of ground connections because they have very permeable stony zones, washed out by water purified by natural filtration, and presenting high resistivity. It may therefore be necessary to cross these layers with earth rods in order to find conductive zones and therefore more favorable to the installation of a high-performance and durable earth connection.

In practice, the resistivity of a soil increases when the humidity level decreases. The geological layers of the subsoil through which water flows are not suitable for the establishment of ground connections because they have very permeable stony areas, washed by water purified by natural filtration and with high resistivity.

It is therefore necessary to cross the geological layers with earth rods in order to find conductive zones and therefore more favorable to the installation of a permanent earth connection.

Understand the importance of earth rods as earthing elements

Depending on the nature of the soil in which it is installed, the rod, as an earth electrode, will promote the dissipation of the fault current in the soil, both in a lightning protection and grounding installation. When it is necessary to use multiple earth rods, they are usually arranged in a crow's foot, triangular, or line pattern.

Soil resistivity values

Soil resistivity
Nature of the groundResistivity (Ω.m)
WetlandsBelow 30
Silt20 - 100
Humus10 - 150
Moist peat5 - 100
Plastic clay50
Marls and compact clays100 - 200
Jurassic marl30 - 40
Clayey sand50 - 500
Siliceous sand200 - 3 000
Bare stony ground1 500 - 3 000
Stone floor covered with grass300 - 500
Soft limestone100 - 300
Compact limestone1 000 - 5 000
Cracked limestone500 - 1 000
Shale50 - 300
Micaschists800
Granite and sandstone according to alteration1 500 - 10 000
Very altered granites and sandstones100 - 600

In order to approximate the resistance of a earth connection, the following average values can be used:/span>

Soil resistivity
Nature of the groundResistivity's average value (Ω.m)
Oily arable land, wet compact fills50
Lean arable land, gravel, coarse fill500
Bare stony soils, dry sand, impermeable rocks3 000

Estimation of the earth resistance

It is possible to determine, in an approximate way, the ground resistance, valid for a homogeneous ground:

  • R : Earth resistance (Ω)
  • ρ : Soil resistivity (Ω.m)
  • N : Number of earth rods
  • l : Length of earth rod (m)

Selecting the earth rod

Discover the characteristics of earth rods

Earth rods characteristics

MALTEP offers a complete range of earth rods according to different selection criteria:

  • Material
  • Dimensions (diameter and length)
  • Means of extension

The resistance of the ground depends mainly on the length of the installed rods and their number. Contrary to popular belief, the diameter has very little influence on the resistance value, as does the material, since the metals used in the manufacture of the rods (copper, steel, etc.) have a much higher conductivity than the soil. When it is difficult to reach the desired resistance of the ground, it is therefore preferable to increase the length of the earth rods, if the nature of the soil allows it, to try to reach more conductive layers at depth, then multiply the number of earth rods if the soil is too hard at depth.

Earth rods material

As standard, MALTEP  earth rods are offered as described below:

The copper bonded steel earth rods are manufactured from a steel core which is placed in an electrolytic bath in order to deposit the required thickness of copper by electrolysis. The purity of the deposited copper is 99.9%. Several thicknesses of copper plating are offered:

  1. Minimum thickness of 254µm
  2. Average thickness of 350µm

The electrolytic coating promotes the longevity of copper-bonded steel earth rod for a long-lasting and durable installation.

Stainless steel earth rods are offered in the following grades:

  1. Z33 C13 stainless steel
  2. 316 (A4) stainless steel

Stainless steel earth rods are preferred for soils with high corrosion characteristics.

Earth rods dimensions and means of extension

As a standard, MALTEP earth rods are manufactured as per table below:

Standard MALTEP earth rods dimensions
Length (m)Nominal Diameter (" - mm)
15/8 - 16
1,53/4 - 19
2-

There are various ways to extend the length of  MALTEP earth rods in order to reach the desired soil layer.

The extension of a non-threaded earth rod can be achieved by using a non-threaded brass coupler.

The extension of a threaded earth rod is accomplished by using a threaded coupler of a diameter compatible with the rod.

As its name indicates, the auto-extensible earth rod does not require any additional accessory in order to realize the extension, it is done by driving the earth rod on the previous one already present in the ground.

Overview of MALTEP earth rods product range

Earth rod to conductor connection

Find out how to connect the earth rod to the earthing conductor

MALTEP solutions for the connection between earth rod and conductor

MALTEP offers different ways to connect the earth rod to the earthing conductor which can be of different shapes such as multi-stranded cable, round or tape:

  • Mechanical clamps with screwed connections
  • Mechanical clamps with knock-in head connections
  • Exothermic welding connections

Overview of the range of connections between earth rods and conductors

Mounting the earth rod

Find out basics information

Information on the mounting of earth rods

Precautions to take when driving an earth rod into the ground

Driving an earth rod into the ground can present several risks to the operator and to the integrity of the earth rod:

MALTEP offers different accessories for the protection of the operator and earth rod when driving in the ground:

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