Why grounding?

Earthing the installation allows the fault current to flow to the ground in the event of an insulation fault. It also ensures discharge of the fault current due to lightning strikes and electromagnetic disturbances.
This earthing will thus ensure:

• The protection of people and their safety
• Protection of property and facilities

What are the elements that make up the earth circuit:

The earth circuit is made up of several elements. They will be in contact with the ground and will diffuse the fault current and the measurement:

• The electrode or earth rod.
• The visit look
• Earth conductor connections
• Earth conductors or earth cables
• The cut-off bar

The resistivity of the ground is very important in the final choice of the elements that make up the earth circuit, in fact the grounds are more or less conductive and their resistivity depends on:

• The nature of the terrain (marshy soil, rock, gravel, sand, etc.)
• Water content (Moisture)
• Climatic variations

The resistivity of the ground is expressed in Ohmmeter and can vary between 10 Ω.m and 10,000 Ω.m, it will depend on the above factors.

Ground resistivity depending on the nature of the ground:

Nature of the land	Resistivity in Ωm
swampy land	1 to 30
silt	20 to 100
humus	10 to 150
wet peat	5 to 100
plastic clay	50
marls and compact clays	100 to 200
Jurassic marls	30 to 40
clay sands	50 to 500
siliceous sands	200 to 300
bare stony ground	1,500 to 3,000
stony ground covered with grass	300 to 500
soft limestones	100 to 300
compact limestones	1,000 to 5,000
cracked limestones	500 to 1000
shale	50 to 300
granite and sandstone	1,500 to 10,000
very weathered granite and sandstone	100 to 600

Resistivity (Ωm) of different terrains (according to NF C 15-100)

Earth measurement by the 62% method

Before the measurement, the cut-off strip must be disconnected in order to isolate the earth electrode from the rest of the installation, thus allowing the earth resistance to be measured periodically.

To carry out the measurement it will be necessary to use a measuring device called Tellurometer.

This method requires the use of 3 stakes. It consists in injecting a current between a first electrode and the earth rod of the installation (or the rod connected to the loop at the bottom of the excavation), the third rod will allow the measurement of the voltage.

To implement this method it is necessary to start from the stake connected to the excavation bottom P1 and place a second stake P2 at more than 10m the third stake P3 will be placed at 62% of the distance (L1) between P1 and P2 this allows ” be outside the zones of influence created by the flow of current. (See diagram below).

If the measurement is not conclusive, it will be necessary to lengthen the earth rod connected to the excavation bottom loop or add one or more earth rods in order to obtain a value less than 100 Ohms.

If the measurement is less than 100 Ohms it will have to be validated by moving P3 to 52% and 72% of P2, if the measurement does not vary, the positioning of P1 can be validated. (See diagram below)

The best solution for creating an earth electrode is the bottom digging loop.

The belt or buckle at the bottom of the excavation is recommended for new constructions.

This solution consists in making a loop with a bare copper or an earth cable around the building figure 4. Bare copper will be placed under the clean concrete or buried 1m below the foundations of the exterior walls. Bare copper must be in direct contact with the ground.

For existing buildings, the bottom conductor must be buried all around the exterior walls of the premises to a depth of at least 1 meter.

Material required to make the earth connection:

Examples of implementation

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