BS 7430:1991

Committees responsible
Foreword
Code of practice
Section 1. General
1 Scope
2 Definitions
Section 2. Earthing and the provision of a path for
earth fault currents
3 Supply system earthing
4 Electrical equipment earthing
5 System and equipment protection
Section 3. Earthing methods
6 Factors involved in effective earthing
7 Soil resistivity
8 Effect of shape on electrode resistance
9 Resistance of common types of earth electrodes
10 Selection of a material for an earth electrode or a
    buried uninsulated earthing conductor
11 Miscellaneous types of electrode
12 Earthing cathodically protected structures
13 Selection of an earthing conductor and connection to
    an electrode
14 Current density at the surface of an earth electrode
15 Potential gradient around earth electrodes
16 Periodic inspection and testing of the earthing
    system and measurement of resistance of installed
    electrodes and earthing conductors
Section 4. Earthing applications
17 Generating plant
18 Power stations and substations
19 Earthing associated with overhead power lines
20 Consumers' electrical installations
21 Temporary scaffolding and similar metallic
    structures
22 Telecommunication circuits and equipment
23 Lightning protection and earthing
24 Mines and quarries
25 Street lighting and other electrically supplied
    street furniture
26 Hazardous areas (potentially explosive atmospheres)
27 Earthing of conductors for safe working
28 Electric traction
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 beta
14 Values of current densities for earthing conductors
Figures
1 TN systems
2 TT and IT systems
3 Effect of buried length of rod or pipe electrode on
    calculated resistance for soil resistivity of 100
    ohm.m (assumed uniform)
4 Effect of inter-electrode spacing on combined
    resistance
5 Calculated and experimental curves of resistance of
    12.5 mm diameter driven rod electrodes
6 Resistance of horizontal strip electrodes
7 Effect of spacing on combined resistance of two
    horizontal strip electrodes
8 Ground surface potentials around a single rod and
    three rods in line
9 Potential gradient in the vicinity of a horizontal
    strip electrode
10 Potential distribution between rod electrodes
11 Measurement of earth electrode resistance
12 Earth resistance curves
13 Measurement of earth resistivity
14 Single low voltage standby generator (without
    paralleling facility)
15 Low voltage standby generators with neutrals
    connected
16 Low voltage standby generators with neutral earthing
    transformers
17 Low voltage standby generators with star-point
    switching
18 Single high voltage standby generating set not
    suitable for parallel operation with incoming mains
    supply
19 Single high voltage standby generating set suitable
    for parallel operation with incoming mains supply
20 Multiple high voltage standby generating sets with
    neutral earthing transformer suitable for parallel
    operation with each other and with the incoming
    mains supply
21 Multiple high voltage standby generating sets
    suitable for parallel operation with each other and
    with the incoming mains supply
22 Low voltage standby generating sets with generator
    transformers giving a high voltage supply and
    suitable for parallel operation with the incoming
    mains supply
23 Earthing arrangement and protective conductors for
    consumers' installations
24 Method of supplying electricity to caravan pitch
    electrical equipment

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.