Earthing Arrangements: What Is it? (Definition, Requirements, Example)

Earthing arrangement (UK and IEC) or grounding arrangement (US): all electrical means involved in the earthing of a system, installation or equipment [definition from IEC 60050-195:2021].

Note 1 to entry: Electric connection and devices used for earthing are examples of electrical means.

General Requirements

The earthing arrangements may be used jointly or separately for protective and functional purposes according to the requirements of the electrical installation. The requirements for protective purposes shall always take precedence.

Where provided, earth electrodes within an installation shall be connected to the main earthing terminal using an earthing conductor.

NOTE. An installation does not need to have its own earth electrode.

Where the supply to an installation is at high voltage, requirements concerning the earthing arrangements of the high voltage supply and of the low-voltage installation shall also comply with Clause 442 of IEC 60364-4-44:2007.

The requirements for earthing arrangements are intended to provide a connection to earth which:

  • is reliable and suitable for the protective requirements of the installation;
  • can carry earth fault currents and protective conductor currents to earth without danger from thermal, thermo-mechanical and electromechanical stresses and from electric shock arising from these currents;
  • if relevant, is also suitable for functional requirements;
  • is suitable for the foreseeable external influences (see IEC 60364-5-51), e.g. mechanical stresses and corrosion.

Consideration shall be given to the earthing arrangements where currents with high frequencies are expected to flow (see Clause 444 of IEC 60364-4-44:2007).

Protection against electric shock, as stated in IEC 60364-4-41, shall not be adversely affected by any foreseeable change of the earth electrode resistance (e.g. due to corrosion, drying or freezing).

Example

On one of the forums I came across a typical project for a earthing arrangement for the electrical installation of an individual house.

Here is an example of the implementation of a earthing arrangement:

Earthing arrangement
Implementation of the earthing arrangement (main earthing terminal is not shown in the figure)

This earthing arrangement is relevant for ground types with design ρ ≤250 Ohm*m and must provide REA ≤ 30 Ohm. And it consists of:

  • 2 vertical earth electrodes, 3 m long, spaced at L ≥ 6 m.
  • 1 horizontal earth electrode, connected to the earthing conductor.
  • A main earthing terminal mounted in the building (not shown in the sketch) connected to the earthing conductor. The main earthing terminal itself is connected by a protective conductor to the protective busbar of the switchgear from which all the protective conductors “start”. The latter are connected to the exposed conductive parts of the electrical equipment.

Some technical details:

  • The earth electrodes are deepened so that their upper part is 0.5 meter below the surface of the ground.
  • The minimum dimensions of earth electrodes and earthing conductor can be found in Table 54.1 [see it after the article]. For example, for a circular vertical earth electrode made in the form of a hot-dip galvanized steel rod, the minimum diameter will be 16 mm. And for horizontal earth electrode and earthing conductor, made in the form of a round wire of the same steel, the minimum diameter will be – 10 mm.
  • Parts of the earth electrode that are in the ground must be joined together by means of electric welding with a double weld. The length of the weld is greater than or equal to the 6 largest diameters of the circular cross-section. That is, if we need to weld two electrodes with a diameter of 20 and 16 mm, the length of weld should be at least 6 * 20 = 120 mm
  • The main earthing terminal must have terminals for the connection of protective conductors and equipotential bonding conductors. These terminals must allow the connection of conductors with a cross-section of ≥ 16 mm2. The main earthing terminal must have one or two terminals for the connection of earthing conductors with a diameter ≥ 10 mm.
  • The number of vertical earth electrodes depends on the resistivity of the ground and the maximum allowable resistance of the earthing arrangement (EA). If the building installation is of the TN-C-S system earthing type, the resistance of the earthing arrangement has no effect on the protection against electric shocks. Here it is necessary to ensure continuity of the PEN conductor to the protective conductor. Therefore, the resistance of the earthing arrangement can be normalized, e.g. by the requirements for lightning protection of the house.
Table 54.1 IEC 60364-5-54-2011
Table 54.1 – Minimum size of commonly used earth electrodes, embedded in soil or concrete used to prevent corrosion and provide mechanical strength [2]

References

  • IEC 60050-195:2021
  • IEC 60364-5-54-2011