ELECTRICAL INSTALLATION DESIGN GUIDE

Transcription

1 ELECTRICAL INSTALLATION DESIGN GUIDE 2nd Edition

2 Published by The Institution of Engineering and Technology, London, United Kingdom The Institution of Engineering and Technology is registered as a Charity in England & Wales (no ) and Scotland (no. SC038698). The Institution of Engineering and Technology is the new institution formed by the joining together of the IEE (The Institution of Electrical Engineers) and the IIE (The Institution of Incorporated Engineers). The new Institution is the inheritor of the IEE brand and all its products and services, such as this one, which we hope you will find useful. 2008, 2013 The Institution of Engineering and Technology First published 2008 ( ) Reprinted September 2008 Reprinted (with amendments) November 2008 Second edition (incorporating BS 7671:2008 (2011)) 2013 ( ) This publication is copyright under the Berne Convention and the Universal Copyright Convention. All rights reserved. Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may be reproduced, stored or transmitted, in any form or by any means, only with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency. Enquiries concerning reproduction outside those terms should be sent to the publishers at The Institution of Engineering and Technology, Michael Faraday House, Six Hills Way, Stevenage, SG1 2AY, United Kingdom. Copies of this publication may be obtained from: The Institution of Engineering and Technology PO Box 96, Stevenage, SG1 2SD, UK Tel: +44 (0) sales@theiet.org While the publisher and contributors believe that the information and guidance given in this work are correct, all parties must rely upon their own skill and judgement when making use of them. The author, publisher and contributors do not assume any liability to anyone for any loss or damage caused by any error or omission in the work, whether such an error or omission is the result of negligence or any other cause. Where reference is made to legislation it is not to be considered as legal advice. Any and all such liability is disclaimed. ISBN Typeset in the UK by Carnegie Book Production, Lancaster Printed in the UK by TBC

3 Contents Cooperating organisations 6 Preface 7 Chapter 1 Design sequence Load characteristics Supply characteristics Installation outline Distribution design Standard final circuits Isolation and switching Final assessment Compliance with BS Chapter 2 Simple installations and final circuits Introduction Supply characteristics Fault rating of switchgear Final circuit overcurrent devices and cables Final circuit voltage drop limitations Fault protection Short-circuit current protection Protective conductors Standard final circuits 24 Chapter 3 Maximum demand and diversity Introduction Installation outline Final circuit current demand Diversity between final circuits Complex installations 34 Chapter 4 Selection of cables for current-carrying capacity Symbols Preliminary design Overcurrent requirements Current-carrying capacity tables 44 3

4 4.4 Protection against overload and short-circuit Protection against fault current only Corrections for grouping not liable to simultaneous overload Motors 56 Chapter 5 Voltage drop Voltage drop in consumers installations Distribution system voltage drop Basic voltage drop calculation Correction for inductance Correction for load power factor Correction for conductor operating temperature Correction for both conductor operating temperature and load power factor 66 Chapter 6 Calculation of fault current Determination of prospective fault current Determined by enquiry Determined by calculation 72 Chapter 7 Shock protection Shock protection Protective measure: automatic disconnection of supply Circuit calculations 83 Chapter 8 Protection against fault current The adiabatic equation Selection from Table Introduction to calculations Simple calculation Energy let-through calculation Plotting protective conductor adiabatics Protective conductor as a sheath or armour of a cable Plotting of cable armour adiabatics Calculation of armour capability Conduit and trunking Earthing and bonding conductors 104 Chapter 9 Calculations associated with testing General Continuity Earth fault loop impedance Z s Reduced section protective conductors 112 4

5 Chapter 10 Impedance of copper and aluminium conductors Introduction Conductor resistance and temperature Impedance of cables from voltage drop tables 116 Chapter 11 Harmonics Introduction Cable ratings Voltage drop Overcurrent protection 123 Chapter 12 Protection against voltage disturbances Introduction The overvoltages Power frequency fault voltage Power frequency stress voltages Earthing of 11 kv substations 129 Chapter 13 Busbar trunking Symbols Voltage drop Fault currents 132 Appendix A Symbols 135 Appendix B Standard final circuits 139 Appendix C Avoidance of unintentional operation of circuit-breakers 155 C.1 Lighting circuit applications 156 Appendix D Further cable calculations 159 D.1 Cable life 159 D.2 Temperatures (core and sheath) 160 D.3 Inductance of cables in parallel 160 D.4 Calculation of sheath voltages 161 Appendix E Symbols from CENELEC report R Appendix F Equipment data 167 Index 187 5

6 Preface This book provides step-by-step guidance on the design of electrical installations, from domestic installation final circuit design to fault level calculations for LV/large LV systems. Apprentices and trainees will find it very helpful in carrying out the calculations necessary for a basic installation. The book has also been prepared to provide a design sequence, calculations and data for a complete design. All necessary cable and equipment data to carry out the calculations is included. Consultants will be able to check the calculations of their design packages. It includes calculations and necessary reference data not found in the design packages, such as cable conductor and sheath temperatures and allowances for harmonics. 7

7 A Adiabatic, equation 2.8, 4.5, 8.1, 8.4 curve plotting 8.6, 8.8 After-diversity demand 3.4 Aluminium, cables Table F.9 coefficient of resistance 10.2, Tables F.4, F.17 conductors Ch. 10 resistance Tables F.1, F.7A, F.8A, F.9 Aluminium strip armour cables Table F.9 Ambient temperature, correction factor 4.3.2, multiplier 4.3.2, Table F.2 Area, steel underfloor trunking Table F.10 Armour, current rating 8.9 Attenuation of fault level Automatic disconnection of supply 7.2 B Basic protection 7.1 Bonding conductors, supplementary BS 88 fuse characteristics 8.6, 8.8 BS 88 fuse disconnection times Tables 8.6, 8.8 BS 3036 fuse disconnection times Table 8.7 BS 7671 Appendix 4 4.3, 4.6, 5.3 Table 4B Table 4C Table Table Table Busbar trunking, general Ch. 13 fault currents 13.3 voltage drop 13.2 C a C c C d C f C g C i C r 6.3.2, 9.3.2, Table F.3 C s C t 5.6 Cable adiabatics 8.8 armour 8.7, Table F.8B armour area Tables 8.9, F.7B, F.8B armour as protective conductor 8.7, Table 8.9 calculations, further Appx D 187

8 core temperature D.2 data Appx F impedance 10.3 life D.1 ratings, harmonics 11.2 reactance D.3 sheath earth 8.7 sheath temperature D.2 voltage drop 10.3 Cables buried in ground Cables, in parallel, inductance D.3 in thermal insulation Calculations final circuit current demand 3.3 current-carrying capacity Ch. 4 motor 4.7 prospective fault levels 6.3 shock protection 7.3 voltage drop 5.3 Cartridge fuse short-circuit capacity 6.1 CENELEC Report R symbols Appx E Certificates 1.8, Circuit-breaker characteristics Appx C, 4.5 energy let-through 8.4.2, 8.5 short-circuit capacity 6.1 unintentional operation Appx C Circuit cooker Ex2 demand 3.3 final Ch. 2, Appx B immersion heater Ex4 lighting Ex3 motor Ex5 protective conductor sizes 2.8, Ch. 8 shower 2.4.1, 2.6, Ex1 Circuits, lightly loaded standard Appx B Coefficient of resistance 10.2, Table F.4 Completion certificates 1.8 Complex installations 3.5 Conductor adiabatics 8.6 impedance Ch. 10 operating temperature 4.3.6, D.2, Table F.3 Conduit 8.10 Continuity testing 9.2 Cooker circuit Ex2 Cooking diversity 3.4 Coordination load, device and cable characteristics 2.4 Copper, coefficient of resistance 10.2, Tables F.4, F.17 conductor resistance Tables F.1, F.6, F.7A, F.8A, F.14, F.15, F.16 conductors Ch. 10 Core temperature D.2 Correction factors 6.3.2, Table F

9 Cross-sectional area, armour Tables F.7B, F.8B steel conduit Table F.10 trunking Table F.10 Current-carrying capacity 4.3 Currents fault Currents overload D Definitions, symbols 4.0, Appx A Demand Ch. 3 commercial Ex1 domestic 3.1, Ex2 final circuit 3.3 Departures from BS Design Ch. 1 Design current I b 2.4 Design, preliminary 4.1 Design responsibility 1.8 Deterioration of cables Appx D Direct contact see Basic protection Disconnection times Distribution circuit, overcurrent protection 4.2 diversity 3.4 Distribution design 1.4 Distribution system, calculations voltage drop 5.2 Distribution transformer impedance Table F.5 Diversity Ch. 3, 3.4 Domestic demand 3.1, Ex2 E Earthing arrangements Earthing conductor Earthing of 11 kv substations 12.5 Embedded generation Equipment tables Appx F External earth fault loop impedance 2.2.3, 6.2 F Fault currents 4.2.1, Ch. 6 busbar trunking 13.3 determined by enquiry 6.2 Fault protection 2.6, 7.1, Fault rating, switchgear 2.3 Fault voltage 12.3 Final circuit 1.5, Ch. 2, 2.9, Appx B demand 3.3 diversity 3.4 formulae Appx B thermal insulation Appx B voltage drop 2.5, 5.1 Formulae, circuits Appx B Fundamental frequency 11.1 Fuse characteristics 4.5, 8.4.1, 8.6, 8.8,

10 G Grouping, three-phase lightly loaded overload 4.6 rating factor H Harmonics Ch. 11 cable ratings 11.2 discharge lamps 11.1 overcurrent protection 11.4 switch mode power supplies 11.1 voltage drop 11.3 Household demand 3.1 HV supplies 1.2 HV system earth faults 12.3 I I 2 t 8.1 characteristics 4.5 energy let-through 8.5 Immersion heater circuit Ex4 Impedance Ch. 10 steel conduit Table F.11 steel trunking Tables F.12, F.13 transformers Table F.5 Indirect contact see Fault protection Inductance of cables in parallel D.3 Inrush current Appx C Installation certificates design overcurrent 4.2 outline 1.3, 3.2 schematic 3.2 small voltage drop Ch. 5 Isolation 1.6 I t tabulated cable rating 2.4.1, J no entries K k factor 8.2 Kitchen demand 3.1 L Lead, coefficient of resistance 10.2, Table F.4 Let-through energy 4.5 Life of cables D.1 Lighting circuits Ex3, Appx B voltage drop 2.5 Load characteristics 1.1 diversity 3.1 power factor voltage drop

11 M Main bonding conductors Maximum demand Ch. 3 Maximum earth fault loop impedance Maximum prospective short-circuit current 6.2 Mineral cable heavy duty Tables F.15, F.16 light duty Table F.14 Motor circuit Ex5, 4.7 Motor diversity 3.4 (mv/a/m) Ch. 5, 10.3 N New supplies 2.2 O Office design Overcurrent devices, cables, circuits 2.4 Overcurrent protection 4.2 Overload currents not simultaneous 4.6 parallel cables protection protection against 4.4 protection, omission 2.4.3, 4.5 small Overvoltage protection Ch. 12 P Parallel cables D.3 Part Peak tripping current Appx C Phase displacement Ch. 11 PME Power factor voltage drop 5.5 Power frequency stress voltages 12.4 Prospective fault current 1.4.3, Ch. 6 Prospective short-circuit currents single-phase Table F.18A three-phase Table F.18B Protection against electric shock 7.1 overload and short-circuit 2.7, 4.4 Protective conductor adiabatic 2.8, 8.3, 8.6, 8.8 armour as 1.4.5, 8.7, 8.8, 8.9 conduit as 8.10 cross-sectional area 8.2 reduced section 1.4.5, 9.4 sheath of cable 8.7 sizes Ch. 8 trunking as 8.10 Protective measures, shock 7.1 PVC cables Tables F.7A, F.7B single-core Table F.6 Q no entries 191

12 R R 1 + R Radial final circuits 2.4.1, Appx B voltage drop 2.5 Rated short-circuit capacities 6.1 Rating factors Reactance of cable D.3 Reduced section, protective conductors testing 9.4 Regulation 28 of ESQCR 6.2 Regulation Regulation Regulation , 4.5 Regulation Regulation , Ch. 6, Regulation Regulation Regulation Regulation Regulation Regulation Regulation Regulation 543 Ch. 8 Regulation Resistance, coefficient 10.2, Table F.4 correction factors 6.3.2, Table F.17 mineral cable Tables F.14, F.15, F.16 of conductors Ch. 10, Table F.1 Rewireable fuses Ring final circuits 2.4.2, Appx B voltage drop 2.5 R , Appx E S Schedule of test results 9.1 Schematic 3.2 Sheath, temperature D.2 voltages D.4 Shock protection 1.4.4, Ch. 7 circuit calculations 7.3 Short-circuits 4.4 capacities switchgear 6.1 current three-phase supply single-phase 2.7, Shower circuit 2.4.1, 2.6, Ex1 Simple installations Ch. 2, Simultaneous overload, not liable 4.6 Single-core cables Tables F.6, F.9 Socket circuits, radial Special installations or locations Standard circuits 1.5, Ch. 2, Appx B Standby systems Star-delta starting 4.7 Starting current Appx C Steel, coefficient of resistance Table F.4 conduit, impedance Table F

13 trunking impedance Tables F.12, F.13 underfloor trunking Table F.10 Storage heater diversity 3.4 Stress voltage 12.4 Submains 3.4 Substations Earthing of 11 kv 12.5 Supplementary bonding conductors Supply, characteristics 1.2, 2.2 earth fault loop impedances 2.2.3, 6.2 fault level attenuation 6.2 system fault levels 6.2 Switchgear fault rating 2.3 short-circuit capacities 6.1 Switching 1.6 Symbols 4.0, Appx A CENELEC Appx E System earthing T Table 4B Tables 4C1 4C Table Tables 54.2 to Table Temperature conductor corrections 7.3 Temperature correction Tables F.2, F.3 Testing Ch. 9 continuity 9.2 earth fault loop impedance 9.3 Thermal insulation final circuits Appx B Thermoplastic cables Tables F.7A, F.7B Thermosetting cables Tables F.8A, F.8B Third harmonics Ch. 11 Three-phase voltage drop TN systems Transformer impedance Table F.5 Triplen harmonics Ch. 11 Trunking 8.10 TT systems Typical distribution system U Unintentional operation, lighting circuits Ch. 1 V Voltage disturbances protection Ch. 12 Voltage drop 1.4.2, 2.5, Ch. 5 busbar trunking 13.2 cables 10.3 conductor operating temperature 5.6 distribution system 5.2 final circuit 2.5 inductance 5.4 lighting circuit 2.5 multiplier C r Table F.3 power factor 5.5 radial final circuit

14 ring final circuit temperature correction 5.6, 7.3 three-phase Voltage factor c Table A.1 Voltages, sheath D.4 W Water heater diversity 3.4 XY no entries Z Z Z e Z s 7.2.3,