Electrical Installation Calculations
For Compliance with BS 7671:2008
Juni 2010
202 Seiten, Softcover
Wiley & Sons Ltd
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.
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
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