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1 INTERNATIONAL STANDARD IEC Second edition Electrical installations of buildings Part 4-43: Protection for safety This English-language version is derived from the original bilingual publication by leaving out all French-language pages. Missing page numbers correspond to the Frenchlanguage pages. Reference number IEC :2001(E)
3 INTERNATIONAL STANDARD IEC Second edition Electrical installations of buildings Part 4-43: Protection for safety IEC 2001 Copyright - all rights reserved No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland Telephone: Telefax: Web: Commission Electrotechnique Internationale International Electrotechnical Commission Международная Электротехническая Комиссия PRICE CODE For price, see current catalogue S
4 IEC: CONTENTS FOREWORD Introduction Scope Normative references Requirements according to the nature of the circuits Protection of phase conductors Protection of the neutral conductor Disconnection and reconnection of the neutral conductor Nature of protective devices Devices ensuring protection against both overload current and short-circuit current Devices ensuring protection against overload current only Devices ensuring protection against short-circuit current only Protection against overload current Co-ordination between conductors and overload protective devices Position of devices for overload protection Omission of devices for protection against overload Position or omission of devices for protection against overload in IT systems Cases where omission of devices for overload protection is recommended for safety reasons Overload protection of conductors in parallel Protection against short-circuit currents Determination of prospective short-circuit currents Position of devices for short-circuit protection Omission of devices for short-circuit protection Short-circuit protection of conductors in parallel Characteristics of short-circuit protective devices Co-ordination of overload and short-circuit protection Protection afforded by one device Protection afforded by separate devices Limitation of overcurrent by characteristics of supply Annex A (informative) Protection of conductors in parallel against overcurrent Annex B (informative) IEC Parts 1 to 6: Restructuring Bibliography Figure A.1 Circuit in which an overload protective device is provided for each of the m conductors in parallel Figure A.2 Circuit in which a single overload protective device is provided for the m conductors in parallel Figure A.3 Current flow at the beginning of the fault Figure A.4 Current flow after operation of the protective device cs Table 43A Values of k for phase conductor Table B.1 Relationship between restructured and original parts Table B.2 Relationship between new and old clause numbering... 37
5 IEC: INTERNATIONAL ELECTROTECHNICAL COMMISSION ELECTRICAL INSTALLATIONS OF BUILDINGS Part 4-43: Protection for safety FOREWORD 1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, the IEC publishes International Standards. Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. The IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested National Committees. 3) The documents produced have the form of recommendations for international use and are published in the form of standards, technical specifications, technical reports or guides and they are accepted by the National Committees in that sense. 4) In order to promote international unification, IEC National Committees undertake to apply IEC International Standards transparently to the maximum extent possible in their national and regional standards. Any divergence between the IEC Standard and the corresponding national or regional standard shall be clearly indicated in the latter. 5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment declared to be in conformity with one of its standards. 6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights. International Standard IEC has been prepared by IEC technical committee 64: Electrical installations and protection against electric shock. The IEC series (parts 1 to 6), is currently being restructured, without any technical changes, into a more simple form (see annex B). According to a unanimous decision by the Committee of Action (CA/1720/RV ( )), the restructured parts of IEC have not been submitted to National Committees for approval. The text of this second edition of IEC is compiled from and replaces part 4-43, first edition (1977) and its amendment 1 (1997), part 4-473, first edition (1977) and its amendment 1 (1998). This publication has been drafted, as close as possible, in accordance with the ISO/IEC Directives, Part 3. Annexes A and B are for information only. The committee has decided that the contents of this publication will remain unchanged until At this date, the publication will be reconfirmed; withdrawn; replaced by a revised edition, or amended. The contents of the corrigendum of August 2002 have been included in this copy.
6 IEC: ELECTRICAL INSTALLATIONS OF BUILDINGS Part 4-43: Protection for safety 430 Introduction (431) 1 Scope Part 4-43 of IEC describes how live conductors are protected by one or more devices for automatic interruption of the supply in the event of overload (see clause 433) and short-circuits (see clause 434) except in cases where the overcurrent is limited in accordance with clause 436 or by the conditions described in 433.3, or are met. Further, protection against overload and against short-circuits shall be co-ordinated in accordance with clause 435. NOTE 1 Live conductors protected against overload in accordance with clause 433 are considered to be protected also against faults likely to cause overcurrents of a magnitude similar to overload currents. NOTE 2 The requirements of this standard do not take account of external influences. For the application of protective measures in relation to conditions of external influences, see of IEC and clause 422 of IEC NOTE 3 Protection of conductors according to this standard does not necessarily protect the equipment connected to the conductors. (433.1 and 434.1) 1 Protective devices shall be provided to break any overcurrent flowing in the circuit conductors before such a current could cause a danger due to thermal and mechanical effects or a temperature rise detrimental to insulation, joints, terminations, or surroundings of the conductors Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this part of IEC For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this part of IEC are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of IEC and ISO maintain registers of currently valid International Standards. IEC :1998, Low-voltage fuses Part 1: General requirements IEC :1986, Low-voltage fuses Part 2: Supplementary requirements for fuses for use by authorized persons (fuses mainly for industrial application) IEC :1987, Low-voltage fuses Part 3: Supplementary requirements for fuses used by unskilled persons (fuses mainly for household and similar applications) IEC : Electrical installations of buildings Part 4-41: Protection for safety Protection against electric shock IEC : Electrical installations of buildings Part 5-52: Selection and erection of electrical equipment Wiring systems 1 In this standard, references in brackets refer to the previous numbering system.