BS 7430:1998

Committees responsible
Foreword
1 Scope
2 Normative references
3 Definitions
4 Supply system earthing
5 Electrical equipment earthing
6 System and equipment protection
7 Factors involved in effective earthing
8 Soil resistivity
9 Effect of shape on electrode resistance
10 Resistance of common types of earth electrodes
11 Selection of a material for an earth electrode or a
    buried uninsulated earthing conductor
12 Miscellaneous types of electrode
13 Earthing cathodically protected structures
14 Selection of an earthing conductor and connection to
    an electrode
15 Current density at the surface of an earth electrode
16 Potential gradient around earth electrodes
17 Periodic inspection and testing of the earthing system
    and measurement of resistance of installed electrodes
    and earthing conductors
18 Generating plant
19 Power stations and substations
20 Earthing associated with overhead power lines
21 Consumers' electrical installations
22 Temporary scaffolding and similar metallic structures
23 Telecommunication circuits and equipment
24 Lightning protection and earthing
25 Mines and quarries
26 Street lighting and other electrically supplied street
    furniture
27 Hazardous areas (potentially explosive atmospheres)
28 Earthing of conductors for safe working
29 Electric traction
Annex A (informative) Typical calculations for various types
of earth electrodes
Bibliography
Figure 1 TN systems
Figure 2 TT and IT systems
Figure 3 Effect of buried length of rod or pipe electrode on
           calculated resistance for soil resistivity of 100 nm
           (assumed uniform)
Figure 4 Effect of inter-electrode spacing on combined
           resistance
Figure 5 Calculated and experimental curves of resistance
           of 12.5 mm diameter driven rod electrodes
Figure 6 Resistance of horizontal strip electrodes
Figure 7 Effect of spacing on combined resistance of two
           horizontal strip electrodes
Figure 8 Ground surface potentials around a single rod and
           three rods in line
Figure 9 Potential gradient in the vicinity of a
           horizontal strip electrode
Figure 10 Potential distribution between rod electrodes
Figure 11 Measurement of earth electrode resistance
Figure 12 Earth resistance curves
Figure 13 Measurement of earth resistivity
Figure 14 Single low voltage standby generators (without
           paralleling facility)
Figure 15 Low voltage standby generators with neutrals
           connected
Figure 16 Low voltage standby generators with neutral
           earthing transformers
Figure 17 Low voltage standby generators with star-point
           switching
Figure 18 Single high voltage standby generating set not
           suitable for parallel operation with incoming
           mains supply
Figure 19 Single high voltage standby generating set suitable
           for parallel operation with incoming mains supply
Figure 20 Multiple high voltage standby generating sets with
           neutral earthing transformer suitable for parallel
           operation with each other and with the incoming
           mains supply
Figure 21 Multiple high voltage standby generating sets
           suitable for parallel operation with each other and
           with the incoming mains supply
Figure 22 Low voltage standby generating sets with generator
           transformers giving a high voltage supply and
           suitable for parallel operation with the
           incoming mains supply
Figure 23 Simplified illustration of single-core cable
           sheath bonding systems
Figure 24 Earthing arrangement and protective conductor
           for consumers' installations
Figure 25 Method of supplying electricity to caravan pitch
           electrical equipment
Tables
1 Examples of soil resistivity
2 Factors for parallel electrodes arranged in line
3 Factors for electrodes arranged in a hollow square
4 Minimum sizes of components for earth electrodes
5 Coefficients for strip or round conductor electrodes
6 Recommended materials for the manufacture of earthing
    components
7 Corrosion resistance of some electrode materials related
    to soil parameters
8 Suitability of materials for bonding together
9 Geometric mean distance z for closely spaced
    reinforcing rods
10 Earth fault current densities for 1 s duration for
    earthing conductors with initial conductor temperature
    of 30 deg C
11 Earth fault currents for copper strip earthing conductors
12 Earth fault currents for aluminium strip earthing conductors
13 Values of K and SS
14 Values of current densities for earthing conductors

Guidance on earthing of electrical supply systems, electrical installations and connected equipment, for the proper operation of systems and the protection of human and animal life. Covers basic principles, earthing methods and most general applications. Certain special applications are covered only by references to other standards.