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1、BRITISH STANDARD BS 921:1976 Specification Rubber mats for electrical purposes UDC 614.825:621.315.61:678.06 Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 02:08:14 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 921:1976 This British Standard, having been prepar
2、ed under the direction of the Personal Safety Equipment Standards Committee, was published under the authority of the Executive Board on 31 March 1976 BSI 02-1999 First published October 1940 First revision January 1952 Second revision March 1976 The following BSI references relate to the work on th
3、is standard: Committee reference PSM/15 Draft for comment 74/61888 DC and draft for approval 75/61741 ISBN 0 580 09363 0 Co-operating organizations The Personal Safety Equipment Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the foll
4、owing Government departments and scientific and industrial organizations: British Footwear Manufacturers Federation British Ironfounders Association British Occupational Hygiene Society British Rubber Manufacturers Association Ltd.* British Safety Council British Steel Industry Cement Makers Federat
5、ion Chemical Industries Association Consumers Association Council of Ironfoundry Association Department of Industry (National Engineering Laboratory) Electricity Supply Industry in England and Wales* Engineering Employers Federation Federation of Civil Engineering Contractors Glass Manufacturers Fed
6、eration Health and Safety Executive* Industrial Safety (Protective Equipment) Manufacturers Association Institute of British Foundrymen Institution of Civil Engineers Institution of Engineering Inspection Institution of Industrial Safety Officers Institution of Mechanical Engineers Institution of Pr
7、oduction Engineers Iron and Steel Trades Confederation Medical Research Council Ministry of Agriculture, Fisheries and Food National Joint Council for the Building Industry (operative side) National Radiological Protection Board Paintmakers Association of Great Britain Royal Society for the Preventi
8、on of Accidents Shoe and Allied Trades Research Association Trades Union Congress The organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this British Standard: Electrical Research Associat
9、ion Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 02:08:14 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 921:1976 BSI 02-1999i Contents Page Co-operating organizationsInside front cover Foreword
10、ii 1Scope1 2References1 3Composition1 4Construction1 5Thickness and width1 6Workmanship and finish1 7Performance requirements1 8Marking1 Appendix A Electrical test2 Appendix B Method for determination of compression set2 Figure 1 Suitable apparatus for determination of compression set3 Publications
11、referred toInside back cover Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 02:08:14 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 921:1976 ii BSI 02-1999 Foreword This British Standard, originally published in 1940, revised in 1952 and confirmed in 1959, has b
12、een revised again to metricate it and to take account of the use of polymers other than natural rubber. The test methods have been amended where necessary in conformity with amended and revised British Standards. It is stressed that rubber mats should not afford the sole means of protection for thos
13、e working on electrical circuits and wherever possible further adequate precautions should be taken against the risk of shock and short-circuit. In this connection attention is drawn to the Electricity (Factories Act) Special Regulations 1908 and 1944. Certification This British Standard provides fo
14、r a product which covers personal safety. Manufacturers and purchasers are urged to make use of the certification facilities described on the inside back cover of this standard. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are
15、responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 4, an inside back cover and a back cover. This standard h
16、as been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 02:08:14 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 921:197
17、6 BSI 02-19991 1 Scope This British Standard deals with insulating mats made of solid natural or synthetic rubber used as floor coverings near electrical apparatus where circumstances involve the possibility of direct contact with conductors whose voltage does not exceed 650 V r.m.s. to earth. The s
18、tandard contains no provisions relating to the use of rubber mats as secondary insulation for conductors at voltages greater than 650 V r.m.s. to earth (see Electricity (Factories Act) Special Regulations 1908 and 1944). This standard is written in terms of metric units. 2 References The titles of t
19、he British Standards referred to in this standard are listed on the inside back cover. 3 Composition Mats shall be made from good-quality raw natural or raw synthetic rubber or from a mixture of these, in conjunction with other suitable compounding ingredients, and shall be free from fabric insertio
20、ns and fibrous materials. Compliance shall be established by visual examination and tests in accordance with clause 7. 4 Construction Mats shall be solid and not perforated. The upper surface may have a ribbed, fluted or other suitable pattern or may be plain. The lower surface may be finished in cl
21、oth imprint. 5 Thickness and width 5.1 Plain mats shall be not less than 6.5 mm in thickness. Patterned mats shall be not less than 6.5 mm in thickness at the root of the pattern. 5.2 Mats shall have a minimum width of 900 mm to accord with the Regulations concerning the minimum width of a working p
22、latform or passageway associated with a switchboard on which there are exposed live conductors (for voltages up to 650). Where the Regulations do not apply the same minimum width is recommended. 6 Workmanship and finish Mats shall be satisfactorily vulcanized, free from blisters, pin holes, cracks,
23、embedded foreign matter and other physical defects. Compliance shall be established by visual examination and tests in accordance with clause 6. 7 Performance requirements 7.1 Insulation. All mats shall be tested in accordance with Appendix A and the leakage current shall not exceed 160 mA/m2 (calcu
24、lated on the area of the smaller electrode) for any position of the electrodes. 7.2 Mechanical. Mats shall be capable of meeting the following requirements. 7.2.1 Tensile stress-strain properties. Test pieces in new condition and test pieces aged for 10 days at 70 C in accordance with method A or me
25、thod B in BS 903-A19:1956 are taken. When tested in accordance with BS 903-A2:1971 and using type 1 or type 2 dumb-bell testpieces, the tensile strength shall be not less than 5 MN/m2 and the elongation at break shall be not less than 250 %. 7.2.2 Compression set. Test pieces in new condition and te
26、st pieces aged for 10 days at 70 C in accordance with either method A or method B of BS 903-A19:1956, shall be subjected to the compression test specified in Appendix B. The resulting compression set shall not exceed 10 % on new or aged test pieces, and the test pieces shall show no signs of crackin
27、g. 8 Marking Mats claiming to comply with this British Standard shall be clearly and indelibly marked as follows: a) the number of this British Standard, i.e. BS 921, b) the date of manufacture, c) the name or identification mark of the manufacturer, d) the words “650 V maximum”. Licensed Copy: Lond
28、on South Bank University, London South Bank University, Fri Dec 08 02:08:14 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 921:1976 2 BSI 02-1999 Appendix A Electrical test A.1 Apparatus. Two electrodes of any convenient size consisting of flat metal sheets with smoothly rounded edges and corners are
29、 connected to a transformer capable of providing test voltages in the range zero to 15 000 V r.m.s., alternating at any convenient frequency between 25 Hz and 100 Hz. The test voltage shall be of approximately sine wave form and the peak factor shall lie within the limits of 5.0 % (1.34 1.49). The p
30、eak value of the test voltage may be measured by a peak voltmeter, in which case the r.m.s. value for the purpose of this specification shall be considered as the peak value so determined divided byalternatively the test voltage may be determined by a voltmeter suitably connected to the input or out
31、put side of the testing transformer and calibrated against a sphere gap in place of the test electrodes. For details of this method reference may be made to BS 358. One pole of the testing transformer may be earthed or both may be insulated, provided that in the latter case the voltages to earth fro
32、m each pole are approximately equal. The output of the testing set (preferably not less than 2 kVA) shall be sufficient to maintain on the test piece the necessary voltage for the maximum time required. The current between the electrodes is measured by means of a milliameter but care is necessary to
33、 ensure that currents other than those through or over the surface of the mat cannot pass through the meter. A switch is provided to short-circuit the meter except when a reading is being taken and/or to provide a relay to short-circuit the meter if the mat breaks down. A.2 Method of test. The mat i
34、s maintained at a temperature of 23 2 C and the electrodes are pressed on it with a pressure of 1 kPa. The test is applied successively so that the whole area of the mat is tested, compatible with the prevention of arcing between the electrodes at the edges of the mat. The voltage is applied to the
35、electrodes, being raised from zero to 15 000 V r.m.s. as rapidly as is consistent with its value being observed on the measuring instrument, but at not less than 1 kV per second. The full test voltage is then maintained for 1 min after which the voltage is diminished rapidly to zero before being swi
36、tched off. Appendix B Method for determination of compression set B.1 Apparatus. The compression apparatus shall consist of parallel platens, between which the test pieces are compressed, and a calibrated loading spring. The platens shall be mounted in a suitable housing having a screw mechanism for
37、 compressing the spring to apply the load to the platens and shall be equipped with a scale graduated to read to the nearest 0.25 mm for measuring the deflection of the spring. The device shall be capable of applying the required load gradually and maintaining it uniformly over the entire top and bo
38、ttom surfaces of the test pieces for the duration of the test. The platens between which the test pieces are compressed shall be sufficiently rigid to withstand the compressive stress without bending. The loading spring shall be made of heat-treated spring steel with ends ground flat and perpendicul
39、ar to the longitudinal axis of the spring, in order to assist in keeping the platens parallel throughout the test. The spring shall comply with the following requirements. a) The graph obtained by plotting loads against deflections shall be substantially a straight line and have a slope of 70 3 N/mm
40、 of compression. b) The deflection under a given load shall not change, as a result of fatigue, by more than 0.25 mm over a period of a year, as indicated by weekly check tests. A suitable apparatus is shown in Figure 1. B.2 Number and size of test pieces. Three test pieces are required. The test pi
41、eces shall be 12.5 0.25 mm square and so cut that their edges are perpendicular to the square faces. Any corrugations on the upper surface of the mat shall be removed and if the mat is cloth marked the surface shall be buffed until the cloth marks are just removed, care being taken to keep the buffe
42、d surface parallel to the opposite surface. B.3 Conditioning and temperature of test. Condition the test pieces at a temperature of 23 2 C for at least 12 h immediately prior to making the test. The temperature throughout the test shall be 23 2 C. B.4 Procedure and conditions of test. Measure the th
43、ickness of each test piece by a micrometer gauge in which the two contact members have convex part-spherical surfaces of 12.5 mm radius, and the foot of which exerts a force of between 0.6 N and 1.2 N on the rubber. 2 2; Licensed Copy: London South Bank University, London South Bank University, Fri
44、Dec 08 02:08:14 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 921:1976 BSI 02-19993 Assemble the test pieces in the compression apparatus so that they are placed symmetrically on the platen. The surfaces in contact with the test pieces shall be parallel. Place sheets of fine glass paper (grade 0 as
45、specified in BS 871) between the test pieces and the platens with the abrasive side against the rubber. Subject the test pieces of a given sample between one pair of platens to a compressive force of 5 300 N applied in a direction normal to their square faces. Leave the test pieces under this load f
46、or 24 h, remove them from the apparatus, allow them to recover for 1 h and then remeasure their thickness at the centre, as described above. For each test piece calculate the percentage difference in thickness before and after compression. Report the average of the three results as the compression s
47、et. If it is desired to carry out the compression test on new and aged test pieces simultaneously, the respective sets of test pieces shall be placed between different pairs of platens, in the compression apparatus. Figure 1 Suitable apparatus for determination of compression set Licensed Copy: Lond
48、on South Bank University, London South Bank University, Fri Dec 08 02:08:14 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 4 blank Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 02:08:14 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 921:1976 BSI 02-1999 Publication
49、s referred to This standard makes reference to the following British Standards: BS 358, Method for the measurement of voltage with sphere-gaps (one sphere earthed). BS 871, Abrasive papers and cloths for general purposes. BS 903, Methods of testing vulcanized rubber. BS 903-A2, Determination of tensile stress-strain properties. BS 903-A19, Accelerated ageing tests. BSI Certification Trade Mark The Kitemark The Kitemark is the registered certification trade mark of the British Standards Institution. A licence to use the Kitemark on or in relation to
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