6.5.3 Earth-electrode resistances of different types of earth electrodes

This chapter provides a technical description, the physical relationships, practical rules of thumb and the planning and implementation principles for the earth resistances R_A of earthing systems. 

The following chapter begins by explaining terms and describing types of earth electrodes and their classification according to location, shape and profile.

Terms and definitions 

Earth is the conductive ground and the part of the earth in electrical contact with an earth electrode whose electric potential is not necessarily zero. The term 'earth' also describes both a place and a material; e.g. humus, clay, sand, gravel and rock.
Reference earth (neutral earth) is the part of the earth, especially the surface of the earth outside the area influenced by an earth electrode or an earth-termination system, in which no perceptible voltages arising from the earthing current occur between two arbitrary points (Figure 6.5.3.1).
An earth electrode is a conductive component that can be embedded in the ground or in a specific conductive medium; e.g. concrete, and is in electrical contact with the ground.
An earthing system is the entirety of electrical connections and devices used to earth a network, a system or a piece of equipment, such as earthing conductors, mast bases, reinforcements or cable metal sheaths.
An earthing conductor is a conductor that establishes a current path or part of a current path between a given point in a network, installation or piece of equipment and an earth electrode. (Example: connecting cable between the main earthing busbar and the earth electrode)
Lightning protection earthing is the earthing of a lightning protection system to dissipate lightning current into the ground.