1、BRITISH STANDARD BS 6907-2: 1988 Electrical installations for open-cast mines and quarries Part 2: General recommendations for protection against direct contact and electric shock UDC 622.3:622.271.3:622.812.2:621.31.005:621.3 784.37:614.8BS6907-2:1988 This British Standard, having been prepared und
2、er the directionof the Mining and Quarrying Requisites StandardsCommittee, was published under the authority ofthe Board of BSI and comesintoeffect on 30 September 1988 BSI 09-1999 The following BSI references relate to the work on this standard: Committee reference MQE/23 Draft for comment 86/75881
3、 DC ISBN 0 580 16369 5 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Mining and Quarrying Requisites Standards Committee (MQE/-) to Technical Committee MQE/23, upon which the following bodies were represented: Associated Offices Techni
4、cal Committee British Coal China Clay Association Electric Cable Makers Confederation Electrical Contractors Association Engineering Equipment and Materials Users Association Federation of Civil Engineering Contractors Federation of Manufacturers of Construction Equipment and Cranes Health and Safet
5、y Executive Independent Engineering Insurers Committee Institution of Mining and Metallurgy Amendments issued since publication Amd. No. Date of issue CommentsBS6907-2:1988 BSI 09-1999 i Contents Page Committees responsible Inside front cover Foreword iii Section 1. General 1 Scope 1 Section 2. Prot
6、ection against electric shock in normal service 2 Protection against direct contact by limitation of voltage 2 3 Complete protection by means of barriers or enclosures 2 4 Protection from contact with overhead line conductors 3 Section 3. Protection against electric shock in case of a fault 5 Genera
7、l 4 6 Power systems 4 7 Protective measures for TN-S systems 7 8 Protective measures for TT systems 7 9 Protective measures for IT systems 8 10 Earth fault current limitation devices 8 11 Earthing arrangements and protective conductors 9 Section 4. Protection against overcurrent and fault current 12
8、 General 14 13 Types of protective device 14 14 Automatic interruption: protection against overcurrent due to overload 14 15 Automatic interruption: protection against short-circuits 15 16 Co-ordination of overcurrent and short-circuit protection 16 17 Limitation of overcurrent by nature of the sour
9、ce 16 Appendix A Selection of factor k for calculating the minimum cross-sectional area of protective conductors 17 Figure 1 Power system TN-S with separate neutral and protective conductors throughout the system 5 Figure 2 Power system TT 5 Figure 3 Power system IT with independent earth electrodes
10、 6 Figure 4 Power system IT with common earth electrode 6 Figure 5 Power system IT using external TT or TN system as a source 6 Figure 6 Illustration of the elements of a typical earthing arrangement 9 Table 1 Minimum size of earthing conductors 10 Table 2 Selection of minimum cross-sectional area f
11、or protective conductors 12 Table 3 Minimum cross-sectional area of aerial and suspended protective conductors 12 Table 4 Minimum cross-sectional area of supplementary equipotential bonding conductors 13 Table 5 Values of k for insulated protective conductors not incorporated incables and not bunche
12、d with cables or for bare protective conductors in contact with cable covering 17 Table 6 Values of k for protective conductor as core in a cable or bunchedwithcables 17 Table 7 Values of k for protective conductor as a sheath or armour of a cable 18BS6907-2:1988 ii BSI 09-1999 Page Table 8 Values o
13、f k for bare protective conductors where there is no riskofdamage to any neighbouring material by the temperatures indicated 18 Publications referred to Inside back coverBS6907-2:1988 BSI 07-1999 iii Foreword This Part of BS6907 has been prepared under the direction of the Mining and Quarrying Requi
14、sites Standards Committee. BS6907 is based on the International Electrotechnical Commissions publication IEC621 “Electrical installations for outdoor sites under heavy conditions (including open-cast mines and quarries)” and, like that publication, is published in Parts as follows. Part 1: Glossary;
15、 Part 2: General recommendations for protection against direct contact and electric shock; Part 3: Recommendations for equipment and ancillaries; Part 4: Recommendations for winning, stacking and processing machinery, pumps and low signal level and communications systems; Part 5: Recommendations for
16、 operation. BS6907 sets out the guiding principles for the installation and operation of electrical equipment so as to ensure safety of persons, livestock, property and the proper functioning of the plant. It applies to the installation and operation of electrical apparatus and systems associated wi
17、th outdoor sites under heavy conditions, including open-cast mines, quarries, stockpiles, etc. It applies particularly to electrical apparatus and systems used for the following: a) winning, stacking and primary processing machinery; b) secondary processing machinery; c) conveyor systems; d) pumping
18、 and water supply systems; e) movable railway systems; f) control, signal, supervisory and communication systems. BS6907 does not cover temporary and provisional places of work in the open, such as building sites and earth-moving sites, unless the equipment used is similar to that used in surface mi
19、ning applications. It takes account of British practice, electrical regulations and law and thereby differs in several respects from the IEC publication. Both cover a subject not previously the subject of an International Standard or a British Standard. A British Standard does not purport to include
20、 all the necessary provisions of a contract. Users of British Standards are 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, pagesi t
21、oiv, pages1to18, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.iv blankBS6907-2:1988 BSI 09-1999 1 Section 1. General 1 Scope This Part of BS
22、6907 gives recommendations for protection against direct contact and electric shock for all installations in normal service, and in cases of fault, overcurrent and fault current. For winning, stacking and processing machinery, pumps and low signal level and communications systems, exemptions from th
23、ese recommendations and supplementary recommendations are given in BS6907-4, which should, therefore, be read in conjunction with this Part. The recommendations given for low voltage installations are essentially from the IEE “Regulations for Electrical Installations” (the Wiring Regulations), as ap
24、plicable. NOTE 1A glossary of terms used in this standard is given in BS6907-1. NOTE 2The titles of the publications referred to in this standard are listed on the inside back cover.BS6907-2:1988 2 BSI 09-1999 Section 2. Protection against electric shock in normal service 2 Protection against direct
25、 contact by limitation of voltage Protection against direct contact is deemed to be ensured where the system is not more than25V a.c. or60V d.c. or where, as a protective measure, safety extra-low voltage or functional extra-low voltage is used. 3 Complete protection by means of barriers or enclosur
26、es 3.1 Protection from live parts All live parts should be contained inside enclosures or behind barriers providing at least the following degrees of protection in accordance with BS5490. 3.2 Strength and stability of barriers and enclosures Barriers and enclosures should be firmly secured in place.
27、 Taking into account their nature, size and arrangement, they should have sufficient stability and durability to resist the strains and stresses likely to occur in normal service. 3.3 Access to installation Where it is necessary to make provision for the removal of barriers, the opening of enclosure
28、s, or the withdrawal of parts of enclosures (doors, casings, lids, covers, etc.), this should be accomplished by one of the following. a) Key or tool. Removal, opening or withdrawal should necessitate the use of a key or tool. b) Interlocking device. An interlocking device should be provided so that
29、 removal, opening or withdrawal without the use of a key or tool necessitates previous switching off of all live parts behind the barrier or enclosure which might be touched accidentally. Restoration of supply should be possible only after replacement or reclosure of the barriers or enclosures. Prov
30、ision should be made for the discharge of stored energy in capacitors or cable systems where they are likely to give rise to the risk of electric shock. c) Automatic disconnection. Removal, opening or withdrawal without use of a key or tool should initiate automatic switching off before live parts b
31、ehind the barrier or enclosure can be touched accidentally. Restoration of supply should be possible only after replacement or reclosure of the barriers or enclosures. d) Internal interposing screen. An internal interposing screen should be so positioned that none of the live parts can be touched wh
32、ile the barrier or enclosure is removed. The screen should be either firmly secured in place or slid into place at the moment the barrier or enclosure is removed except where used as a second barrier see item e). It should not be removable except by means of a tool or key. Such a screen may be a pro
33、tective shutter which, in the case of a disconnectable assembly, slides into place in front of the feed line contacts. e) Access to control circuit components. Where any parts within an enclosure need occasional handling (such as the replacement of a lamp or of a fuse-link, instrument settings or ad
34、justment of electronic controls) removal, opening or withdrawal without the use of a key or tool and without switching off should be possible only if the following conditions are simultaneously fulfilled. 1) A second barrier suitably labelled is provided within the enclosure so as to prevent persons
35、 from coming accidentally into contact with live parts. It should not be possible to remove the second barrier except through the use of a key or tool. Low voltage Complete protection IP2X or IP4X for top surfaces or barriers or enclosures which are readily accessible. This applies in particular to
36、those parts of enclosures which might serve as a standing surface. Above 1000 V Complete protection IP5X within arms reach. Partial protection IP2X beyond arms reach.BS6907-2:1988 BSI 09-1999 3 2) The voltage of all live parts behind the second barrier does not exceed660V. 3.4 Additional protection
37、for cable conductors All cables external to the equipment should be fully insulated for the system voltage and, where this exceeds125V a.c. or250V d.c., provided with suitable metallic covering. 4 Protection from contact with overhead line conductors 4.1 Where use of overhead lines is essential, the
38、y have to be constructed and maintained in accordance with the overhead lines regulations 1) . However, the maximum height of vehicles likely to be used may require ground/lowest conductor clearances greater than those specified in the regulations. 4.2 Where an existing overhead line is within the q
39、uarry curtilage, special care should be exercised to prevent the possibility of contact of cranes, excavators, or other high vehicles, e.g. dump trucks and tipping lorries. Reference should also be made to BS6907-5. 1) “Avoidance of danger from overhead lines”, HSE Guidance note GS6 “Overhead lines
40、regulations for securing the safety of the public” Factories Act 1961. Electricity Regulations.BS6907-2:1988 4 BSI 09-1999 Section 3. Protection against electric shock in case of a fault 5 General 5.1 The protective measures recommended in this section are intended to prevent a touch voltage from pe
41、rsisting for such a length of time after the occurrence of a fault that danger to persons or livestock could arise. The measures have been developed from experience and consideration of the probability of persons or livestock being in indirect contact and of the nature of the plant involved in the f
42、ault situation. Protection should be afforded in the case of an earth fault by either automatic disconnection of supply within specified conditions of voltage and time, or limitation of indirect contact voltage below the conventional voltage limit at which disconnection of the supply is not required
43、. In this section, the protective measures against indirect contact with a protective conductor for all installations with voltages up to and including1000V and those above1000V are described. NOTEThe recommendations for installations for voltages up to and including1000V are taken from the IEE “Reg
44、ulations for Electrical Installations” (the Wiring Regulations). 5.2 It is essential that exposed conductive parts be connected to a protective conductor. The earthable point of the power system and protective conductor should be connected to an earth electrode near the respective power transformer
45、or generator. If good earthing facilities or points are available, the protective conductor should be connected to them at as many places as possible. NOTEMultiple earthing at points distributed as evenly as possible may be necessary in order to ensure that the potential of the protective conductor
46、remains as close as possible to the earth potential in case of fault. This protective conductor may be a bare conductor, that is, without a covering of insulating material. 5.3 A protective device should automatically disconnect the supply to that part of the electrical installation protected by the
47、 device, if, following a fault in that part, the touch voltage cannot be maintained at any point of the installation at a value equal to or less than the conventional touch voltage limit U L , where U L= 50V r.m.s. For evaluation of touch voltage the operating current and/or the characteristics of t
48、he protective device should be used. NOTE 1In certain configurations of IT systems, automatic disconnection may not be required on the occurrence of the first fault. NOTE 2For nominal voltage to earth of240V a.c., disconnection may be achieved by compliance with regulation 413-5 of the IEE “Regulati
49、ons for Electrical Installations” (the Wiring Regulations). NOTE 3It may be necessary to specify lower values than50V for certain applications or locations, for example wet and conductive environments. 5.4 In particular installations (for example, systems supplying motors) up to and including1000V where a clear and permanent distinction can be made between a) those parts of the installation which supply only fixed apparatus, and b) those parts intended to supply portable and mobile apparatus having exposed conductive part
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