Domestic Wiring

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This is a guide for domestic wiring.

Text of Domestic Wiring



    MAY 2009

    Technical Information Series Publication No: TIS001, Edition 1


    Technical Information Series Publication No: TIS001, Edition 1


    Sponsored by:


    Colombo 3.

  • Foreword

    This publication on Domestic Wiring is the first in a Technical Information Series that the Institution of Engineers, Sri Lanka (IESL) has decided to publish. It was during the Session 2003/ 2004 that the then Electrical and Electronic Engineering Sectional Committee of the IESL first decided on the need for a publication on this subject. This was considering the fact that many who presently undertake residential wiring and electrical installation work often overlook certain important factors that mostly affect the safety of the public. At present, electrical household wiring is designed and installed generally by unqualified Electricians whose knowledge and competency on the subject is questionable. In the bygone days, only the electricians who registered themselves with the Local Authorities were authorized to undertake household wiring. However, this rule is not being implemented any more. With the wide scale electrification of the country, a large number of unskilled workers have taken up work as electricians. The sub standard designs and installations done by these workers pose a grave risk not only to the occupants of the houses concerned but also to those living in the neighboured of those houses. To make matters worse, there is very little reading material available to educate and guide those who are interested to learn and update their knowledge so that they carry out their work according to laid out standards.

    Eng. J Mallikarachchi, who was a member of the Electrical and Electronic Engineering Sectional Committee during the Session 2003/2004 and who was well conversant with the subject is the author of this Monograph. He in compiling this publication has combined his own practical experience together with the theoretical knowledge acquired by reading various other publications available on the subject. The main focus of the publication has been on educating the reader on the IEE wiring regulations explained in simple terms while retaining their meanings.

    This publication on Domestic Wiring will certainly fill this void. While the contents are simple and easy to understand

  • with no complicated mathematical calculations or drawings, it is comprehensive enough to cover all fundamental aspects that one needs to know on the subject. The Monograph is based on the 16th Edition of the IEE Wiring Regulations which was the standard that was being followed at the time of writing it although it is the 17th Edition that is now in practice. This however does not make the contents outdated in any way.

    We will also be shortly arranging for the translation of the book in to Sinhala so as to benefit a larger cross section of readers.

    Finally we take this opportunity to thank Eng. Ranjith Gunawardana, the Immediate Past President, who as the then Chairman of the Electrical and Electronic Sectional Committee during the Session 2003/2004 realised the need for this publication, the Author Eng. J Mallikarachchi, the Past Presidents, Eng. D. G. Senadhipathi and Eng. B. R. O. Fernando who assisted the Author in editing the publication, Eng. (Prof) J R Lucas, Eng. M Zubair and Eng. Ranil Senaratne for their valuable contributions in making the document more comprehensive. Finally we thank the Members of the Library, Publications and Publicity Committee (LPP&C) of the current session for their contributions towards making this monograph a reality.

    Eng. D P MallawaratchiePresident of IESL Session 2008/2009

    Eng (Prof) AKW JayawardaneVice President and Chairman LPP&C 2008/2009


    Scope 11Introduction 12

    Basics of electrical wiring 13 Control of supply 13 Protection 13 Conductor 13 Insulator 13 Cables 13 Additional protection for cables 13 Stranding of conductors 14 Flexible cords 14 Electric circuits 14 Relationship between voltage and current 15 The basic circuit 15 Waveform 16 Types of available a. c. supplies 16 Current carrying capacity 16 Overcurrent 17 Faults short circuits 17 Earth faults 17 Direct and indirect contacts 18 Prevention of fires and accidents 18 Switching 19 Switches 19 Isolator 19 Fuse 19 Circuit breaker 19 Emergency disconnection 20 Voltage and current rating of equipment 20 Earth fault protection 20 Resistance area of earth electrode 21 Earth loop impedance 22 Earth leakage circuit breakers 22 Voltage operated earth leakage circuit breaker 22 Residual current circuit breaker 23 Residual current device 24 Distribution inside the house 24 Distribution board 24 Final circuit 24 Fixed wiring 24 Socket outlet 25 Electrical point 25

  • Different types of final circuits 25 Sequence of supply controls 26 Declared or nominal voltage 27 Accessory 27 Diversity 27 The consumer unit 27 Safety precautions 27 Types of switches 29 Wiring systems additional protection for cables 30 Looping in system 30 Identification (Colour code) 31 Single line diagram 31IEE Regulations 33

    Summary of Regulations relevant to domestic wiring 35

    Fundamental Principles 35 Protection for safety 35 Protection against electric shock 35 Protection against thermal effects 35

    Requirements for safety 35 Conductors and equipment 35 Fuses and circuit breakers 36 Connection of switches 36 Emergency disconnection 36 General provision for earthing 36 Installation of equipment 36 Special conditions 36 Addition to an installation 36 Testing and inspection 36 Control distribution and over-current protection 37 Protective equipment 37 Control of supply 37 Isolation 37 Overcurrent protection 38 Protection against electric shock 39 Protection against direct contact 39 Protection against indirect contact 39 Earthed equipotential bonding 39 Circuit protective conductors 40 Connection with earth 41 Labelling 41 Maximum demand and diversity 41 Nature of demand 41 Final circuits 42 Conductors and cables: choice and construction 42

  • Voltage rating 42 Current rating 42 Voltage drop 42 Cross-sectional area of conductors 42 Protection against mechanical damage 42 Identification of conductors 43 Terminations 43 Installation of equipment 43 Lamp holders 43 Lighting points 44 Ceiling roses 44 Lighting fittings 44 Plugs and socket-outlets 44 Switching for safety 46

    EXCERPTS FROM PREVIOUS EDITIONS 47 Earth fault currents 47 Detached buildings 47 Diversity 47 Overcurrent protection 47 Provision of protective devices 47 Final circuits 48 Final circuits of rating exceeding 15A 48 Domestic ring and radial circuits 48 Bending radius of cables 49 Terminations 49 Conduit systems 49 Metal conduit systems 50 Flexible conduit systems 50 Suspension from non-metallic boxes 51 Equipment liable to cause overheating 51 Ceiling roses 51 Isolated metal 51 Electrical discharge circuits 51 Earth fault protection 51 Room containing a bath 52 From the ON-SITE GUIDE 53 Maximum demand and diversity 53 Conventional circuit arrangements 55 Final circuits using 13A socket-outlets 55 Circuit protection 55 Conductor size 56

  • Cooker circuits in household premises 56 Correction factors for current carrying capacity 56

    Selection of a System 59 Conductors 59 Insulation 59 Wiring systems 60 Overcurrent Protection 60 Means of isolation 61 Earth fault protection 62 Distribution boards 62 Layout 62 Type of final circuits 65 Selection of cables 65 Voltage drop calculation 67 Lighting circuits 68 Socket outlet circuits 68 Conduit capacities 69

    Planning the installation 71 Example 75 Installation 83 Conduits on walls and ceilings 84 Conduits for switches 84 Conduits for socket outlets 85 Conduits for distribution boards 86 Wiring 86 Example 88 Single line diagram 89 Conduit layout 89 Wiring procedure 90

    Testing 95 Tests to be carried out 95 Continuity of earth conductors 97 Continuity of ring final circuits 98 Insulation resistance 100 Earth electrode resistance 102 Operation of residual current devices 103

    New colour code for cable cores 105 Regulation on Warning notice Non standard colours 106

  • FROM THE APPENDIX: HARMONIZED CABLE CORE COLOURS 107 Introduction 107 Alteration or addition to an existing installation 107 Single phase 107 Two- or three-phase installation 107 Switch wires 108 Intermediate and two-way switches 108 Phase conductors 108 Changes 108 References 112

    List of Diagrams

    Fig.1 Components of a cable 13Fig.2 Stranding of conductors 14Fig.3 Series and parallel circuits 15 Fig.4 Basic domestic circuit 15Fig.5 A.C. Voltage Wave 16 Fig.6 Electrical faults 17 Fig.7 Direct and indirect contacts 18Fig.8 Multi pole switches 19 Fig.9 Earth conductor 21 Fig.10 Resistance area 22Fig.11 Voltage operated earth leakage circuit breaker 23Fig.12 Residual curr