Electrical Installation Calculations

Professor Mark Coates, ERA Technology Ltd, Surrey, UKProfessor 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

• About the authors viiPreface ixAcknowledgements xiSymbols xiiiDefinitions xv1 Calculation of the cross-sectional areas of circuit live conductors 1General circuits 4Circuits in thermally insulating walls 5Circuits totally surrounded by thermally insulating material 6Circuits in varying external influences and installation conditions 6Circuits in ventilated trenches 8Circuits using mineral-insulated cables 9Circuits on perforated metal cable trays 10Circuits in enclosed trenches 11Circuits buried in the ground 14Grouped circuits not liable to simultaneous overload 18Circuits in low ambient temperatures 24Grouped ring circuits 26Motor circuits subject to frequent stopping and starting 27Circuits for star-delta starting of motors 29Change of parameters of already installed circuits 30Admixtures of cable sizes in enclosures 33Grouping of cables having different insulation 392 Calculation of voltage drop under normal load conditions 40The simple approach 40The more accurate approach taking account of conductor operating temperature 43The more accurate approach taking account of load power factor 55The more accurate approach taking account of both conductor operating temperature and load power factor 58Voltage drop in ring circuits 59Voltage drop in ELV circuits 623 Calculation of earth fault loop impedance 65The simple approach 70The more accurate approach taking account of conductor temperature 75Calculations taking account of transformer impedance 81Calculations concerning circuits fed from sub-distribution boards 82Calculations where conduit or trunking is used as the protective conductor 87Calculations where cable armouring is used as the protective conductor 944 Calculations concerning protective conductor cross-sectional area 101Calculations when the protective device is a fuse 104Calculations when an external cpc is in parallel with the armour 111Calculations when the protective device is an mcb 113Calculations when the protective device is an RCD or RCBO 1195 Calculations related to short circuit conditions 126a.c. single-phase circuits 127The more rigorous method for a.c. single-phase circuits 135a.c. three-phase circuits 1416 Combined examples 153Appendix: The touch voltage concept 175Index 189

"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." (Broadcastnewsroom, 20 October 2010).