ISBN 978-0-626-28761-0 SOUTH AFRICAN NATIONAL STANDARD Earthing of low-voltage (LV) distribution systems Published by SABS Standards Division 1 Dr Lategan Road Groenkloof Private Bag X191 Pretoria 0001 Tel: +27 12 428 7911 Fax: +27 12 344 1568 www.sabs.co.za SABS
Table of changes Change No. Date Scope Foreword This South African standard was approved by National Committee SABS/TC 067/SC 05, Electricity distribution systems and components Electricity distribution, in accordance with procedures of the SABS Standards Division, in compliance with annex 3 of the WTO/TBT agreement. This document was published in July 2013. This document supersedes SANS 10292:2001 (edition 1.1). Annex A is for information only. Introduction This document was prepared to ensure that appropriate earthing practices are used by all suppliers of electricity, and to establish and promote uniform use and understanding of the earthing of different types of low-voltage distribution systems and the descriptions, definitions and abbreviations associated with those systems. The five basic types of system earthing illustrated in IEC 60364-1, IEC 60364-5-51 and IEC 60365-5-55 are described in this document, and reasons are given why only two of the five types are prescribed.
Contents Page Foreword Introduction 1 Scope... 3 2 Normative references... 3 3 Definitions... 4 4 LV earthing... 7 5 Types of system earthing... 8 5.1 System earthing identification code... 8 5.2 Overview of types of LV system earthing... 9 6 Characteristics of recommended systems... 13 6.1 General... 13 6.2 TN-C-S system earthing... 13 6.3 TN-S system earthing... 14 7 Earthing requirements for preferred LV distribution systems... 14 7.1 Earthing requirements common to both T-N-C-S and TN-S systems... 14 7.2 Distributor earthing requirements specifically for TN-C-S system earthing... 16 7.3 Distributor earthing requirements specifically for TN-S system earthing... 16 7.4 Service connection requirements... 17 8 Earth connections... 19 8.1 Supply transformers and associated metalwork... 19 8.2 Low-voltage distribution system earthing... 19 8.3 Earthing information... 19 9 Interconnections and extensions... 20 9.1 Interconnection of systems with different power sources... 20 9.2 Extension of one system by another of a different type... 20 10 Testing... 22 10.1 General... 22 10.2 Source earth resistance test... 22 10.3 Voltage and polarity test... 22 10.4 Earthing loop impedance test... 23 Annex A (informative) Typical earthing arrangements... 24 Bibliography... 29 1
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Earthing of low-voltage (LV) distribution systems 1 Scope 1.1 This standard gives requirements and recommendations for the provision of a safe electricity supply to the consumer. 1.2 This standard establishes general principles for the earthing of low-voltage distribution systems of which the supply starts at the point of generation or transformation, and ends at the supply earth terminal of the consumer. 1.3 This standard applies to distributors that operate at a voltage (a.c. or d.c.) that does not exceed 1 000 V. NOTE 1 Earthing practices for the purposes of lightning protection and over-voltage protection are covered in SANS 10313, SANS 10142-1 and SANS 10198-3. NOTE 2 This standard is not intended to be applied to existing systems. 1.4 This standard does not cover special earthing requirements at customers' installations, for example, where a radio frequency earthing is to be installed. For such installations, special precautions might be needed. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Information on currently valid national and international standards can be obtained from the SABS Standards Division. IEC 60364-1, Low-voltage electrical installations Part 1: Fundamental principles, assessment of general characteristics, definitions. IEC 60364-5-51, Electrical installations of buildings Part 5-51: Selection and erection of electrical equipment Common rules. IEC 60364-5-55, Electrical installations of buildings Part 5-55: Selection and erection of electrical equipment Other equipment. SANS 1063, Earth rods, couplers and connections. SANS 10142-1, The wiring of premises Part 1: Low-voltage installations. SANS 10199, The design and installation of earth electrodes. 3