08-30132181-DC.pdf

a Date: 29 August 2008 Origin: National Latest date for receipt of comments: 31 OCTOBER 2008 Project no.: 2005/00951 Responsible committee: GEL/600 Earthing Interested committees: GEL/600/-/2 Title: Draft BS 951 Electrical earthing - Clamps for earthing and bonding - Specification Supersession information: If this document is published as a standard, the UK implementation of it will supersede BS951:1999 and partially supersede NONE. If you are aware of a current national standard which may be affected, please notify the secretary (contact details below). WARNING: THIS IS A DRAFT AND MUST NOT BE REGARDED OR USED AS A BRITISH STANDARD. THIS DRAFT IS NOT CURRENT BEYOND 31 OCTOBER 2008. This draft is issued to allow comments from interested parties; all comments will be given consideration prior to publication. No acknowledgement will normally be sent. See overleaf for information on commenting. No copying is allowed, in any form, without prior written permission from BSI except as permitted under the Copyright, Designs and Patent Act 1988 or for circulation within a nominating organization for briefing purposes. Electronic circulation is limited to dissemination by e-mail within such an organization by committee members. Further copies of this draft may be purchased from BSI Customer Services, Tel: +44(0) 20 8996 9001 or email cservicesbsigroup.com. British, International and foreign standards are also available from BSI Customer Services. Information on the co-operating organizations represented on the committees referenced above may be obtained from the responsible committee secretary. Cross-references The British Standards which implement International or European publications referred to in this draft may be found via the British Standards Online Service on the BSI web site http:/www.bsigroup.com. Direct tel: 020 8996 7721 Responsible Committee Secretary: Mr Ian Richardson (BSI) E-mail: ian.richardsonbsigroup.com Draft for Public Comment Head Office 389 Chiswick High Road London W4 4AL Telephone: +44(0)20 8996 9000 Fax: +44(0)20 8996 7001 Form 36 Version 8.0 DPC: 08/30132181 DC Licensed CopyChinese University of Hong Kong, 21/10/2008 03:09, Uncontrolled Copy, (c) BSI b Introduction Your comments on this draft are invited and will assist in the preparation of the resulting British Standard. If no comments are received to the contrary, this draft may be implemented unchanged as a British Standard. Please note that this is a draft and not a typeset document. Editorial comments are welcomed, but you are advised not to comment on detailed matters of typography and layout. Submission of comments The guidance given below is intended to ensure that all comments receive efficient and appropriate attention by the responsible BSI committee. 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A link to the BSI British Standards Draft Review system, or to a specific draft hosted on the system, may be distributed to other interested parties so that they may register and submit comments. It is not necessary to purchase a copy of the draft in order to review or comment on it; however, additional copies of this draft may be purchased from BSI, Tel: +44(0) 20 8996 9001 or email: cservicesbsigroup.com. Drafts and standards are also available in PDF format for immediate download from the BSI Shop http:/www.bsigroup.com/Shop. Licensed CopyChinese University of Hong Kong, 21/10/2008 03:09, Uncontrolled Copy, (c) BSI WARNING. THIS IS A DRAFT AND MUST NOT BE REGARDED OR USED AS A BRITISH STANDARD. THIS DRAFT IS NOT CURRENT BEYOND 31 OCTOBER 2008. 1 Electrical earthing Clamps for earthing and bonding Specification Licensed CopyChinese University of Hong Kong, 21/10/2008 03:09, Uncontrolled Copy, (c) BSI WARNING. THIS IS A DRAFT AND MUST NOT BE REGARDED OR USED AS A BRITISH STANDARD. THIS DRAFT IS NOT CURRENT BEYOND 31 OCTOBER 2008. 2 Contents Foreword 3 1 Scope 4 2 Normative references 4 3 Terms and definitions 4 4 General 5 5 Construction 5 6 Material 7 7 Electrical characteristics 7 8 Non-slipping torque 8 9 Marking 8 Annexes Annex A (normative) Tests for electrical impedance and temperature rise 9 Annex B (normative) Short-time withstand current test 11 Annex C (normative) Torque test 13 Bibliography 15 List of figures Figure A.1 Test arrangement 10 Figure B.1 Test arrangement 12 Figure C.1 Apparatus for the torque test 13 List of tables Table 1 Termination reference and conductor size 6 Table 2 Maximum torques for screws 6 Table A.1 Test currents for temperature rise 10 Table B.1 Test currents for short-time withstand current (based on IEC 60364-5-54 Table A.54.2) 12 Table C.1 Non-slipping torque values 14 Licensed CopyChinese University of Hong Kong, 21/10/2008 03:09, Uncontrolled Copy, (c) BSI WARNING. THIS IS A DRAFT AND MUST NOT BE REGARDED OR USED AS A BRITISH STANDARD. THIS DRAFT IS NOT CURRENT BEYOND 31 OCTOBER 2008. 3 Foreword This British Standard is published by BSI and came into effect on XX Month 200X. It was prepared by Technical Committee GEL/600. It supersedes BS 951:1999, which is withdrawn. Annex A, Annex B and Annex C are normative. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal obligations. Licensed CopyChinese University of Hong Kong, 21/10/2008 03:09, Uncontrolled Copy, (c) BSI WARNING. THIS IS A DRAFT AND MUST NOT BE REGARDED OR USED AS A BRITISH STANDARD. THIS DRAFT IS NOT CURRENT BEYOND 31 OCTOBER 2008. 4 1 Scope This British Standard specifies performance and mechanical requirements for clamps used to provide mechanically and electrically sound means of earthing and/or bonding, which are primarily intended for use in electrical installations for the connection of: a) earthing conductors, having a cross-sectional area in the range 2.5 mm2 to 70mm2, to earth electrode rods or other means of earthing; b) bonding conductors to metal tubes of circular cross-section that have circumferences of not less than 18.8 mm (i.e. diameters of not less than 6 mm). NOTE 1 These clamps are also suitable for electrically bonding other conductive parts, where at least one is a tube of circular cross-section. Such clamps are not intended for connection to the armour or sheath of a cable. NOTE 2 Clamps specified in this standard are intended to be used singly. NOTE 3 There is no correlation between the size of the conductor which the clamp conductor can accommodate and the size of tube to which it is intended to be fitted. 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. BS EN 1057, Copper and copper alloys Seamless, round copper tubes for water and gas in sanitary and heating applications BS EN 13601, Copper and copper alloys Copper rod, bar and wire for general electrical purposes BS ISO 1456, Metallic coatings Electrodeposited coatings of nickel plus chromium and of copper plus nickel plus chromium ISO 2081, Metallic coatings Electroplated coatings of zinc on iron or steel ISO 2093, Electroplated coatings of tin Specification and test methods IEC 60364-5-54, Electrical installations of buildings Part 5-54: Selection and erection of electrical equipment Earthing arrangements, protective conductors and protective bonding conductors 3 Terms and definitions For the purposes of this British Standard, the following terms and definitions apply. 3.1 tube metal conduit, pipe or rod 3.2 terminal conductive part of the conductor clamping unit required for the mechanical clamping and the electrical connection of the conductor(s), including the parts which are necessary to ensure the correct contact pressure. IEC 60999-1, modified Licensed CopyChinese University of Hong Kong, 21/10/2008 03:09, Uncontrolled Copy, (c) BSI WARNING. THIS IS A DRAFT AND MUST NOT BE REGARDED OR USED AS A BRITISH STANDARD. THIS DRAFT IS NOT CURRENT BEYOND 31 OCTOBER 2008. 5 4 General The clamp shall comprise: a) a device for making electrical contact with the tube; b) a means of tightening the device on to the tube and maintaining tightness; c) a means of termination separate from the arrangement given in item b) for attaching the protective conductor to the device in item a). The clamp shall be provided with a label or other permanent marking warning against the removal of the clamp, which shall have a means of being securely fixed either to the clamp or the protective conductor (see 5.5). 5 Construction 5.1 General The clamp shall be such that effective electrical and mechanical contact can be made and maintained between the clamp and tubes with diameters within the range for which the clamp is intended. The clamp shall make mechanical contact as specified in Clause 8. The design of the clamp shall be such that its attachment to the tube is not likely to result in the deformation of the latter. 5.2 Electrical connections Electrical connections, including the connection to the tube, shall be designed in such a way that contact pressure is not transmitted through insulating material, other than ceramic, pure mica or other material with relevant characteristics, unless there is sufficient resiliency in the metallic parts to compensate for any possible shrinkage or creep of the insulating material. 5.3 Terminals Terminals shall be such that effective electrical contact can be made and maintained between the clamp and an attached protective conductor. The clamp with the terminal(s) in place shall be such that it can make electrical contact as specified in Clause 7. The form of construction of the terminal shall ensure that the conductor, solid or stranded, can be held captive in the clamping unit without deformation of the conductor to an extent which is likely to be detrimental to its strength and energy handling capability. NOTE The terminal may be of a screwed or screwless construction. When a conductor is clamped by the end of a screw bearing directly upon it, the screw end shall be profiled so as not to damage the conductor. Compliance shall be checked by inspection. A screw terminal shall be capable of accepting one of the following: a) a conductor clamped under a screw head provided with a captive washer so that the screw head does not act directly on the conductor; or b) a single conductor clamped directly by a screw threaded arrangement, the cross- sectional area of the conductor being within the range specified in Table 1; or Licensed CopyChinese University of Hong Kong, 21/10/2008 03:09, Uncontrolled Copy, (c) BSI WARNING. THIS IS A DRAFT AND MUST NOT BE REGARDED OR USED AS A BRITISH STANDARD. THIS DRAFT IS NOT CURRENT BEYOND 31 OCTOBER 2008. 6 c) a bolted-on cable socket from a range of sockets which can accommodate conductors having cross-sectional areas covering the whole range specified in Table 1. Clamps having terminals in accordance with a) or b) shall be marked in accordance with 9.1c). It shall be possible to loop in and out of a screw-threaded arrangement with an unbroken conductor. Table 1 Termination reference and conductor size Termination reference Nominal cross-sectional area of conductor mm2 A 2.5 B 4 C 6 D 10 E 16 F 25 G 35 H 50 I 70 5.4 Screws Screws which are used: a) in a screw-threaded arrangement in a termination; or b) for attaching a cable socket to a termination; or c) for tightening the appropriate part of the clamp on to the tube shall be capable of sustaining, without loss of function, the application of the appropriate torque specified in Table 2. Table 2 Maximum torques for screws Nominal diameter of screw Torque Type I screwsA Type II screwsB mm Nm Nm Up to and including 2.8 0.2 0.4 Over 2.8, up to and including 3.0 0.25 0.5 Over 3.0, up to and including 3.2 0.3 0.6 Over 3.2, up to and including 3.6 0.4 0.8 Over 3.6, up to and including 4.1 0.7 1.2 Over 4.1, up to and including 4.7 0.8 1.8 Over 4.7, up to and including 5.3 0.8 2.0 Over 5.3, up to and including 6.0 2.5 A Grub screws which, when tightened, do not protrude from the hole, and other metal screws which cannot be tightened by a tool wider than the minor diameter of the threaded hole. B Other metal screws. Licensed CopyChinese University of Hong Kong, 21/10/2008 03:09, Uncontrolled Copy, (c) BSI WARNING. THIS IS A DRAFT AND MUST NOT BE REGARDED OR USED AS A BRITISH STANDARD. THIS DRAFT IS NOT CURRENT BEYOND 31 OCTOBER 2008. 7 5.5 Warning provision A permanent label or marking provided with each clamp shall be durably marked in a legible type not less than 3 mm high with the words “SAFETY ELECTRICAL CONNECTION DO NOT REMOVE” in addition to the information given in 9.1a) and b) where this information is not given on the clamp. 6 Material Metal components, including current-carrying parts, shall have mechanical strength and electrical conductivity (in the case of current-carrying parts). All components shall have resistance to corrosion adequate to the conditions of the intended use (see 9.2). Compliance is checked by inspection and, if necessary, by chemical analysis. The following metals and coatings can be used in normal conditions of chemical pollution. Stainless steel containing at least 13% chromium and not more than 0.09% carbon. Phosphor bronze. Alloy of copper with additional protection, e.g. tin or nickel. Steel with a suitable protection, such as: an electroplated coating of zinc according to ISO 2081, the coating having a thickness of at least 20 µm; an electroplated coating of nickel and chromium according to BS IS0 1456, the coating having a thickness of at least 20 µm; an electroplated coating of tin according to ISO 2093, the coating having a thickness of at least 20 µm. Others coatings with an equivalent degree of protection can be used. No part shall be made of unalloyed copper. All parts of the clamp using material less than 1 mm thick shall be inherently re