Electrical Installation Calculations

Manual calculations are still extensively used and in particular
are necessary for checking and verifying various software
calculation design packages. It is highly recommended that users of
such software familiarise themselves with the rudiments of these
calculations prior to using the software packages.

This essential book fills the gap between software and manual
calculations. It provides the reader with all the necessary tools
to enable accurate calculations of circuit designs. Rather than
complex equations, this book uses extensive worked examples to make
understanding the calculations simpler. The focus on worked
examples furnishes the reader with the knowledge to carry out the
necessary checks to electrical cable sizing software
programmes.

Other key features include:

• Updated information on 230 volt references and voltage drop
  under normal load conditions

• New sections on buried cables that take into account soil
  thermal conductivity, trenches and grouping, allowing readers to
  carry out accurate cables sizing

• Information and examples of steel wired armour cables, new to
  this edition. This includes sufficiency during short circuits and,
  for cables with externally run CPCs, gives unique fault
  conditions.

• Covers calculations of cross-sectional areas of circuit live
  conductors

• Earth fault loop impedances

• Protective conductor cross-sectional areas and short circuit
  conditions

• Short circuit protection.

The last chapter combines all of the calculations of the
previous chapters to enable the reader to complete an accurate
design of an installation circuit under all conditions.

A unique tool for detailed electrical installation trade,
Electrical Installation Calculations, Fourth Edition is
invaluable to electricians, electrical designers, installers,
technicians, contractors, and plant engineers. Senior electrical
engineering students and technical colleges, junior engineers, and
contracts managers will also find this text useful.

Autorentext

Professor Mark Coates, ERA Technology Ltd, Surrey, UK
Professor Coates is an internationally renowned expert on current ratings for high and low voltage cable systems. He joined ERA Technology in 1983 and is currently Head of Cables at ERA's Engineering Consultancy business. His areas of expertise include measurement of the thermal properties of cable materials, calculation of heat flow through complex thermal paths, MV partial discharge, breakdown testing and life prediction using statistical analysis. He has been one of the leading contributors to the work of IEC Technical Committee 20 (Electric Cables).
Professor Coates is an active member of the IEE/BSI Committee concerned with electrical installations, BS7671. Before joining ERA, he spent several years as a plant engineer in the chemical and textile industry.

Mr Brian D. Jenkins, (deceased), formerly British Standards Institution

Zusammenfassung
Manual calculations are still extensively used and in particular are necessary for checking and verifying various software calculation design packages. It is highly recommended that users of such software familiarise themselves with the rudiments of these calculations prior to using the software packages.

This essential book fills the gap between software and manual calculations. It provides the reader with all the necessary tools to enable accurate calculations of circuit designs. Rather than complex equations, this book uses extensive worked examples to make understanding the calculations simpler. The focus on worked examples furnishes the reader with the knowledge to carry out the necessary checks to electrical cable sizing software programmes.

Other key features include:

• Updated information on 230 volt references and voltage drop under normal load conditions
• New sections on buried cables that take into account soil thermal conductivity, trenches and grouping, allowing readers to carry out accurate cables sizing
• Information and examples of steel wired armour cables, new to this edition. This includes sufficiency during short circuits and, for cables with externally run CPCs, gives unique fault conditions.
• Covers calculations of cross-sectional areas of circuit live conductors
• Earth fault loop impedances
• Protective conductor cross-sectional areas and short circuit conditions
• Short circuit protection.
  The last chapter combines all of the calculations of the previous chapters to enable the reader to complete an accurate design of an installation circuit under all conditions.

A unique tool for detailed electrical installation trade, Electrical Installation Calculations, Fourth Edition is invaluable to electricians, electrical designers, installers, technicians, contractors, and plant engineers. Senior electrical engineering students and technical colleges, junior engineers, and contracts managers will also find this text useful.

Inhalt

About the authors vii

Preface ix

Acknowledgements xi

Symbols xiii

Definitions xv

1 Calculation of the cross-sectional areas of circuit live conductors 1

General circuits 4

Circuits in thermally insulating walls 5

Circuits totally surrounded by thermally insulating material 6

Circuits in varying external influences and installation conditions 6

Circuits in ventilated trenches 8

Circuits using mineral-insulated cables 9

Circuits on perforated metal cable trays 10

Circuits in enclosed trenches 11

Circuits buried in the ground 14

Grouped circuits not liable to simultaneous overload 18

Circuits in low ambient temperatures 24

Grouped ring circuits 26

Motor circuits subject to frequent stopping and starting 27

Circuits for star-delta starting of motors 29

Change of parameters of already installed circuits 30

Admixtures of cable sizes in enclosures 33

Grouping of cables having different insulation 39

2 Calculation of voltage drop under normal load conditions 40

The simple approach 40

The more accurate approach taking account of conductor operating temperature 43

The more accurate approach taking account of load power factor 55

The more accurate approach taking account of both conductor operating temperature and load power factor 58

Voltage drop in ring circuits 59

Voltage drop in ELV circuits 62

3 Calculation of earth fault loop impedance 65

The simple approach 70

The more accurate approach taking account of conductor temperature 75

Calculations taking account of transformer impedance 81

Calculations concerning circuits fed from sub-distribution boards 82

Calculations where conduit or trunking is used as the protective conductor 87

Calculations where cable armouring is used as the protective conductor 94

4 Calculations concerning protective conductor cross-sectional area 101

Calculations when the protective device is a fuse 104

Calculations when an external cpc is in parallel with the armour 111

Calculations when the protective device is an mcb 113

Calculations when the protective device is an RCD or RCBO 119

5 Calculations related to short circuit conditions 126

a.c. single-phase circuits 127

The more rigorous method for a.c. single-phase circuits 135

a.c. three-phase circuits 141

6 Combined examples 153

Appendix: The touch voltage concept 175

Index 189