Code of Practice for Low Voltage Electrical Installations on Railway Network Premises

Transcription

1 for Low Voltage Electrical Installations on Railway Network Submitted by... K J Thompson Nominated Responsible Manager Approved by... B J Wojtas Standards Manager Authorised by... J R Mitchell Chairman, Electrification and Plant Subject Committee Synopsis It is necessary to supplement BS 7671, The Requirements for Electrical Installations, because of the possible interaction between the different electrical power supplies found on or around the rail network. The information contained within this has been used to supplement BS7671 and to comply with the Electricity at Work Regulations and the Health and Safety at Work Act. This document is the property of Railtrack. It shall not be reproduced in whole or in part without the written permission of the Controller, Safety Standards. Published by Safety & Standards Directorate Railtrack Railway Technical Centre London Road Derby Copyright 1994 Railtrack

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3 Page 1 of 21 Contents Section Description Page Part A Issue record 2 Distribution 2 Disclaimer 2 Supply 2 Part B 1 Purpose 3 2 Scope 3 3 Definitions 3 4 Supply voltages 3 5 Protection and switching 5 6 Special requirements near electrified lines 8 7 System design 13 8 Special installations and locations 13 9 Equipment standards Maintenance and testing 17 Appendices A Approved suppliers of Residual Current Devices (RCDs) for use in D.C. electrified areas 18 B Typical circuit design record sheet 19 References 20 RAILTRACK 1

4 Page 2 of 21 Withdrawn Document Part A Issue record This will be updated when necessary by distribution of a complete replacement. Amended or additional parts of revised pages will be marked by a vertical black line in the adjacent margin. Issue Date Comments 1 Jun 94 Original document Distribution Controlled copies of this should be made available to all people who are responsible for designing, specifying, installing or altering low voltage electrical installations in premises on the rail network. Disclaimer The Safety & Standards Directorate (S&SD) shall use its best endeavours to ensure that the content, layout and text of its documents are accurate, complete and in line with current best practice insofar as is reasonably practicable. It makes no warranties, express or implied, that compliance with all or any of its documents shall be sufficient to ensure safe systems of work or operation. The S&SD will not be liable to pay compensation in respect to the content or subsequent use of its standards, except where it can be shown to have acted in bad faith or there has been wilful default. Supply Controlled and uncontrolled copies of this must be obtained from the TDCC Manager, Document Services, Railway Technical Centre, London Road, Derby, DE24 8UP. 2 RAILTRACK

5 Page 3 of 21 Part B 1 Purpose It is necessary to supplement BS7671, "The Requirements for Electrical Installations", because of the possible interaction between the different electrical power supplies found on or around the rail network. The information contained within this has been used to supplement BS7671 and to comply with the Electricity at Work Regulations and Health and Safety at Work Act. 2 Scope The contents of this apply to all Low Voltage electrical installations in premises on the rail network. 3 Definitions 3.1 Low Voltage Normally exceeding 50V A.C. or 120V D.C. ripple free, whether between conductors or to earth but not exceeding 1000V A.C. or 1500V D.C. between conductors, or 600V A.C. or 900V D.C. between conductors and earth. 3.2 Rail network The railways which used to be in the ownership of the British Railways Board up to Domestic environment A location such as an office where the environment is relatively clean and no heavy work activities are undertaken. 3.4 Industrial environment A location such as a workshop where contaminants may be present and there may be heavy machinery. 3.5 Track circuit Part of the signalling system used to detect the presence of trains on a particular section of railway. 3.6 Underground location A location which is sub-surface or totally covered such as a rafted station development as Fire Precautions Act - Sub-surface Railways Construction site A location where building works are in progress and electrical supply installations are of a temporary nature. 4 Supply voltages 4.1 The choice of supply voltage will depend on the equipment nature, location and rating, together with any special safety considerations appropriate to the installation. The majority of supplies will fall into the following categories: Nominal voltage Voltage above earth 50V, 1 phase, centre tap earthed 25V 110V, 1 phase, centre tap earthed 55V 110V, 1 phase, isolated and earth-free V, 1 phase 240V 415V, 3 phase and neutral 240V 650V, 1 phase, isolated and earth-free V, 1 phase centre tap earthed 425V RAILTRACK 3

6 Page 4 of 21 Withdrawn Document b) b) c) b) c) b) c) b) c) Typical applications 50V, 1 phase, centre tap earthed Hand held filament bulb inspection lamps. Portable tools and appliances (while existing equipment is available). 110V, 1 phase, centre tap earthed Temporary lighting installations. Portable tools and appliances in Workshops, Depots and Construction sites. Hand held fluorescent inspection lamps to BS V, 1 phase, isolated and earth-free Electric switch heating and buffer stop lighting. Trackside supplies for the Civil Engineer. Any equipment for use on or close to railway track where electrical earths should not be introduced in order to avoid the risk of interference with signalling equipment. 240V, 1 phase In domestic environments. In workshops, depots, etc., where 110V equipment is not available or if existing equipment must be retained. Power distribution for outdoor/trackside equipment, e.g. switch heating, level crossing supplies, etc. 415V, 3 phase and neutral High power electrical equipment (e.g. electric lifting jacks, welders,). Power supply distribution. Train pre-heating shore based power supplies. 650V, 1 phase, isolated and earth-free Power supplies for signalling systems. 850V, 1 phase, centre tap earthed Train pre-heating shore based power supplies. 4.3 The installation requirements for each category of supply voltage are as follows b) 50V, 1 phase, centre tap earthed The supply should be derived from an isolating transformer to BS3535 Part 1, with secondary winding centre tapped to earth. The secondary side of the transformer should incorporate double pole protection compatible with the rating of the outgoing circuit. 4 RAILTRACK

7 Page 5 of b) c) b) b) b) 110V, 1 phase, centre tap earthed The supply should be derived from an isolating transformer to BS3535 Part 1, with secondary winding centre tapped to earth. The secondary side of the transformer should incorporate double pole protection compatible with the rating of the outgoing circuit. Consideration should be given to the use of an RCD suitable for personnel protection on each circuit incorporating socket outlets. 110V, 1 phase, isolated and earth-free The supply should be derived from an isolating transformer to BS3535 Part 1. Application details are covered in the relevant documents for Electric Switch Heating and Buffer Stop Lighting, see References. 240V, 1 phase All socket outlet circuits in a power supply distribution system should be protected by an RCD unit. The rated tripping current should not exceed 30mA for 30ms. Socket outlets for computers should, where possible, be dedicated i.e., segregated from other supplies. 415V, 3 phase and neutral All socket outlet circuits in power supply distribution systems should be protected by an RCD unit. The rated tripping current should not exceed 30mA for 30ms. 650V, 1 phase, isolated and earth-free The requirements for Electrical Power Supplies for Signalling Systems are detailed in GM/RT1102: 850V, 1 phase centre tapped earth The requirements for shore-based supplies are detailed separately from this, see References. High frequency supplies These supplies (e.g. 125V, 3 phase, 200Hz) are obtained from rotary or static converters, which change both frequency and voltage. The supply from this equipment should be suitably protected. Flexible cables associated with appliances operated on this system should be of the copper braided screened type. 5 Protection and switching 5.1 Fuses Re-wireable type fuses should not be used, however this requirement is not retrospective Cartridge fuses should comply with BS88 or BS1361 as appropriate. RAILTRACK 5

8 Page 6 of 21 Withdrawn Document 5.2 Miniature circuit breakers (MCBs) MCBs, complying with BS3871, may be used to protect final circuits. Care should be taken to select the correct type and rating to match the circuit duty, noting that the methods used to determine device ratings vary with manufacturer MCBs have a relatively low maximum fault current rating and backup fuse protection may be necessary MCBs should not be installed in a way that encourages their use as a switching device to control the circuit supplied (e.g. used as a light switch). 5.3 Residual Current Devices (RCDs) When considering the use of an RCD, reference should be made to Health & Safety Executive (HSE) Guidance Notes No. GS27 and PM An RCD measures the earth leakage current by comparing the current in each conductor which, under normal conditions, will balance. Imbalance will happen when leakage current passes through the earth conductor, fortuitous earth paths, or the operator s body. As the recognised safe limit for sustained electric shock current to an average person is 30mA for 30ms, an RCD provided for personnel protection should have a rated tripping current not exceeding this value All RCDs should be installed and maintained in accordance with the provisions of the relevant Engineering Instructions and procedures, see References Where installations include computer equipment, an RCD incorporating pulsating D.C. fault current should be used. Final circuits designed for connection of computer equipment should, where possible, be dedicated and should limit the total number of appliance that may be connected to the circuit Special types of RCD, immune to direct current, are required in D.C. electrified areas (see Appendix A) Where it is necessary to install RCDs in series, care should be taken to ensure that discrimination is achieved, e.g. by the use of time-delayed devices Earth leakage currents flowing through the body under fault conditions will produce a momentary electric shock. Where appliances are used in hazardous situations, for example, where there is a danger of falling or when using high pressure water jet cleaners, the use of an earth monitoring device in addition to an RCD should be considered. 6 RAILTRACK

9 Page 7 of Earth core monitoring or earth proving device The system provides a pilot conductor to the device, usually in the form of a cable braid, which forms a loop with the main earth conductor. The continuity of the earth path is proven by passing a small electrical current through the loop. If the earth path is not continuous, or if it has a resistance higher or lower than set values, the power supply will not be energised The detection system should be protected against the small D.C. earth leakage currents produced by D.C. electrification system 5.5 Earth screened leads - The provision of an earth conductor in the form of a woven braid or screen surrounding the live conductors ensures that if the lead is crushed or penetrated by a sharp object, there is a strong possibility of the live conductor being connected to earth. A worthwhile improvement in safety is therefore achieved where appliances are used in very arduous conditions. However, the increased rigidity and weight of the lead may limit its use on smaller appliances. 5.6 Double insulation - A major risk of electrocution occurs in the event of a live conductor coming into contact with the case of an appliance. The provision of double insulation to BS2754 or BS2769 (Class II) effectively removes the risk of contact between the case of an appliance and internal live components. Equipment of this type does not require to be earthed, however, there is still danger from a damaged lead exposing live conductors. 5.7 Mechanical protection General - Adequate means of protection should be provided to minimise the risks of mechanical damage to equipment from external influences. Due account should be taken of vibration and seismic disturbances experienced close to railway running lines Trackside cables Cables for use in a trackside location are particularly vulnerable to damage and should preferably be installed in concrete or similar troughing, or as an alternative, buried in the ground. Installation of troughing should be such that obstruction of safe cess areas, etc., are strictly avoided Buried cables should be protected, marked and identified in accordance with GM/TT Existing troughing should only be used when agreement has been granted Where cables are installed in multi user troughing then suitable identification tape should be applied to the cables at regular intervals in accordance with local instructions. RAILTRACK 7

10 Page 8 of 21 Withdrawn Document 5.8 Environmental protection - The risk of attack from water, oils, grease and chemicals (e.g. from rail vehicle washing plant) should be considered. A suitable IP classification, as detailed in BS5490, should be specified. 5.9 Fire protection - Special precautions are required in locations classed as underground. This includes the use of Low Smoke and Fume (LSF) cables. Further information regarding the application of LSF cables can be found in the appropriate standards documents, see References Isolation Circuit breakers and isolators should, wherever possible, be provided with a means for locking in the open or off condition. Devices should not be locked in the closed or on state. When accidental operation could cause severe difficulties (e.g. supply for fire detection equipment), means other than locking should be used (e.g. location, removable cover, prominent labelling) Isolating devices should break the phase and neutral conductors on single phase circuits Isolating devices should break the phase conductors and, preferably, the neutral conductor on 3 phase circuits. 6 Special requirements near electrified lines 6.1 A.C. electrified lines General - The overhead contact wire is charged at a potential of 25,000V. Electric trains draw power from the overhead wire with current returning to the substation via the running rails, return conductors or aerial earth wire depending upon the specific location design. Each overhead line equipment (OLE) support mast is bonded to the traction return rail and provides an earth path through the mast foundation Earthing and bonding Conductive structures and services, where there is a risk of exposed metalwork becoming electrically connected to live OLE (by flashover, breakage of conductors, etc.), should be bonded to the traction return system. This will ensure rapid disconnection of the traction power supply in the event of a fault Additionally, equipotential bonding is required where it is possible to simultaneously touch exposed metalwork and the running rails, trains or other conductive objects connected to the traction return system. This is necessary to limit touch potentials to a value no greater than 25V (normally) or 430V (traction system fault condition) All bonding should be installed in accordance with EHQ/SP/D/101 for Earthing and Bonding on A.C. Electrified Lines. 8 RAILTRACK

11 Page 9 of Application of bonding Structures falling onto live equipment Tall metallic towers, masts, columns and high level fittings, etc., which could fall onto live electrification equipment, including return conductors, should be bonded to the traction return system When a direct bond is made using a standard bond (19/3.25 hard drawn aluminium cable, PVC sheathed, or equivalent), a threaded stud (M16 or 5/8") is required on the structure for the connection. The standard bond will be provided and installed by the electrification department When the structure is part of a low voltage (l.v.)electrical installation, the bonding may be achieved either directly or via the electrical system circuit protective conductor (cpc) (see section 6.1.4) Live equipment falling onto structures - Exposed metallic structures or electrical equipment should be bonded to the traction return system if any of the following cannot be achieved: a minimum clearance of 2.75m from live OLE, or the area directly beneath it, including return conductors; b) a minimum clearance of 2.75m from any running rail Fault current capacity Each metallic part and bonding or protective conductor in the fault path should be capable of carrying the maximum prospective traction system fault current Fault current magnitude and duration will depend on the distance to the nearest electrification feeder station, however, a fault of 5,500A for 0.2s may be considered as a maximum Loop connections - Multiple connections to the traction return system creating parallel and loop circuits should be avoided. Failure to do so may result in a proportion of the normal traction current flowing through these parallel paths Low voltage electrical equipment Direct bonding When electrical equipment is either directly bonded to the traction return system, or is in contact with a conductive structure having a direct bond to the traction return system, the l.v. supply cpc should not be connected to the equipment. This is necessary to avoid creating a parallel path for traction current RAILTRACK 9

12 Page 10 of 21 Withdrawn Document Separation is achieved by "gapping" the supply cable armouring by: the use of an insulated gland, or; b) cutting back the cable armouring to a maximum distance of 300mm from the equipment entry point. Heavy duty heat shrink sleeving should be applied to cover the gland, the cut back section, and 150mm of the cable outer sheath Any additional cpc should be terminated before reaching the equipment A suitable traffolite warning label (attached to the cable by cable ties) should identify that the incoming service cable earth has been "gapped" and should not be bridged An equipotential bond is required between the traction return system and the l.v. supply main earth to provide earth fault protection for the equipment and minimise touch potentials. This will be a standard bond provided and installed by the electrification department in consultation with the Regional Electricity Company (REC) For calculation purposes, the earth loop path via the traction return system will be considered equivalent to the case where a normal earth connection is provided Gapped circuits should have RCD protection Bonding via electrical system earth (indirect bonding) When electrical equipment requires to be bonded, but is not in contact with any metalwork which itself is connected to the traction return system, an alternative to direct bonding of the equipment is required The equipment cpc provides a fault path which is completed by an equipotential bond between the l.v. supply main earth and the traction return system The rating of the cpc should be adequate to carry the prospective traction fault current. A minimum of 16 sq mm copper or equivalent is considered acceptable The equipotential bond is a standard bond provided and installed by the electrification department The final choice whether to bond directly or indirectly will depend on the cost of providing a reinforced cpc compared to direct bonding and the practicality of segregating the earth systems at the appliance or elsewhere. 10 RAILTRACK

13 Page 11 of Non-electrification high voltage supplies Where a high voltage (h.v.) distribution circuit supplies numerous l.v. systems from two or more substations, it is necessary to ensure that parallel paths for traction current are not created via the h.v. cable armouring. This may be likely if the l.v. earths are individually connected to the traction return and the h.v. and l.v. earth systems were to be connected together It may also be necessary to segregate the h.v. and l.v. earths in the presence of dual A.C. and D.C. electrified lines to minimise circulation of stray direct current. Additionally, the REC may refuse agreement to connect supply and h.v. earth systems together In the event that h.v. and l.v. earth systems are segregated, additional precautions should be taken to minimise the possibility of unacceptable touch potentials occurring. Any l.v. derived services in the h.v. substation should be supplied from a suitably rated and positioned isolating transformer It may also be necessary to provide an insulated barrier in the h.v. substation where metallic structures are incorporated in the building fabric and the building is bonded to traction return Special signing may be required to warn against inadvertent interconnection of the segregated earth systems (e.g. restrictions on the use of electrical extension leads). 6.2 D.C. electrified lines General Power is drawn from the grid onto an h.v. distribution network. This network supplies rectifier substations located along the electrified route where the h.v. is converted to a nominal 750V D.C Trains collect power from a third rail and current returns to the substation via the running rails. The running rails are not deliberately earthed but allowed to "float" electrically about true earth, leakage earths maintaining a safe voltage Effects of D.C. electrification As a result of the high traction current levels and corresponding voltdrop, the running rails may rise to 30V above earth. Also, because the running rails are not electrically insulated from the ground, the track ballast, surrounding area and the conductive framework of buildings nearby will take up a D.C. voltage between true earth and the running rail potential. RAILTRACK 11

14 Page 12 of 21 Withdrawn Document Direct current will flow when equipment earthed at one potential makes contact with a conductive object at a different earth potential. In the case of an electrical appliance, this current will flow in the earth lead. It may also produce an arc where contact with the appliance occurs. Overheating is possible in the earth lead and possibly the cpc of the electrical distribution system Non-electrified sidings in an electrified area will normally carry traction currents unless fitted with Insulated Block Joints (IBJs) and should be treated as electrified lines Protection against direct current leakage Special precautions are required where any socket outlet, within 30m of a running rail at traction potential, may provide power to an electrical appliance to be used on or about an object in contact with the running rail. The same requirements apply to inspection pit lighting installations A resistor of 470 ohms, 50 watts should be inserted between the socket earth pin and the main earth connection at each socket outlet to limit D.C. leakage current in the earth wire This resistor will greatly increase the earth loop impedance and, therefore, a D.C. immune RCD should be provided. The sensitivity of a conventional RCD may be dramatically reduced by a relatively small D.C. leakage current passing through the neutral which saturates the magnetic circuit. Suppliers of approved devices are tabled in Appendix A As the neutral conductor is earthed at the supply point and neutral to earth faults can remain undetected, any neutral-earth fault would allow D.C. to bypass the earth resistor. Restrictions on the use of neutral connections apply as follows: for a 415V, 3 phase supply there should be no neutral connection at the socket outlet. Any neutral necessary for control circuits should be derived from an isolating transformer mounted on the appliance; b) for a 110V or 240V supply, the supply should be derived from a BS3535 isolating transformer, centre tapped to earth A special exemption to the Factories Act exists to allow 50V equipment to be used without an earth conductor. 12 RAILTRACK

15 Page 13 of 21 7 System design 7.1 General - Design of l.v. installations should, as far as possible, be in accordance with BS7671 and as supplemented by this. A typical circuit design record sheet is attached as Appendix B of this document. 7.2 Information technology equipment (IT) Power supply circuits for I.T. equipment should, where possible, be segregated from other circuits. The number of equipments which can be supplied from any circuit will be limited due to the relatively high earth leakage currents produced. Allowance should be made for this during the design stage Reference should be made to CP-PM Column lighting - The regulations concerning "highway power supplies and street furniture" apply to equivalent structures on railway premises, such as column lighting and associated distribution equipment located, for example, in car parks and on station platforms. 7.4 Earthing - Metallic conduit, trunking, etc. should not be used as a cpc. 8 Special installations and locations 8.1 Underground locations - Special requirements exist for electrical installations in underground locations and are detailed in GO/ZT Uninterruptible power systems (UPS) UPS are normally associated with data processing equipment and provide a constant power supply independent of failure of the mains system A low power portable UPS may be used in conjunction with a single desk-top computer providing an earth-free supply without any form of "first fault" monitoring, ie. a fault may be present without any warning to the user A larger, fixed installation will require means for emergency shutdown to be provided. The siting of the shut-down controls should be agreed with the local fire-officer since the disconnection of the electrical mains input to the building will not affect the UPS output. 8.3 Interlocking of alternative power supplies Where electrical power is provided to an installation from independent sources, and these should never be connected together, suitable interlocking should be provided to prevent paralleling of these supplies Interlocking should be achieved by a combination of mechanical and electrical devices Reference should be made to HSE Guidance Note No. PM53. RAILTRACK 13

16 Page 14 of 21 Withdrawn Document 8.4 Temporary power supplies All temporary power supplies should be fitted with RCD protection. This is particularly important for supplies provided in a construction site environment which are at increased risk from physical damage Petrol driven generator/alternator sets should not be employed in tunnels, underground and sub-surface locations Reference should be made to HSE Guidance Note No. GS Trackside installations General Cables operating at a voltage 110V, running between the track and associated track side equipment, should be protected against physical damage where the length exceeds 5m Cables operating at a voltage 110V, running to track side equipment, should be protected against physical damage These installations should be such that obstruction in safe cess areas, etc., is strictly avoided Surface track crossing - cables operating at a voltage 110V Should be installed in orange coloured upvc pipe to cross individual tracks. Orange pipe should not be used between adjacent tracks (i.e. 6 foot and 10 foot). The orange pipe should be installed flush with the finished level of the ballast, not protrude beyond the ends of the bearers and be positioned mid-way between adjacent bearers Under track crossing - cables operating at a voltage >110V Should be installed in under track crossings at a minimum depth of 1.2 m below rail level In locations such as sidings, where it can be demonstrated that there is no risk of damage to cables, then surface crossings may be used provided that suitable mechanical protection is installed. 8.6 Equipment in contact with railway track To minimise the risk of interference with signalling track circuits, it is essential that there is no connection between any electrical power supply earth system and any running rail or rail connected structure. All electrical equipment attached to a rail or rail connected structure should be energised from an earthfree, isolated power supply operated at a voltage 110V e.g.: 14 RAILTRACK

17 Page 15 of electric switch heating (the heater units are attached to the track); buffer stop lighting (the light unit may be mounted on the buffer stop structure) The above requirement, however does not necessarily apply to non track circuited areas such as within depot confines. 8.7 Inspection pit lighting - Lighting and associated distribution equipment require protection from mechanical damage and ingress of water, oil and chemical substances. Light fittings should conform to BS5490 classification IP65 as a minimum standard. 8.8 Signals and Telecommunications accommodation - The requirements for Electrical Power Supplies for Signalling Systems are detailed in Railway Group Standard GM/RT Equipment standards 9.1 Plugs and sockets Domestic environment - Power socket outlets should be of the 13A type to BS1363 and should be switched Industrial environment - Where equipment is used in an industrial environment, where sockets are situated out of doors, or, if the power points could be interfered with by a member of the general public, then all socket outlets should be of an industrial pattern and should switch all poles. The following standards should apply: 50V and below - plugs and sockets should be to BS196 or BS4343, with fused plugs where available; b) 110V, 1 phase - plugs and sockets should be to BS4343 coloured yellow; c) 240V, 1 phase - plugs and sockets should be to BS4343 coloured blue; d) 415V, 3 phase - plugs and sockets should be to BS4343 coloured red; e) high frequency supplies - plugs and sockets should be to BS4343 coloured green. 9.2 Trailing and extension leads for voltages 240V, 1 phase Trailing leads should be kept as short as possible (not exceeding 2m) Extension leads should be kept as short as possible, not exceeding 2m in free standing situations and not exceeding 6m where the extension lead is routed and clipped Where a multiway socket block outlet and extension lead is used to facilitate the connection of computer equipment, etc., the outlet should be secured to a suitable medium, such as a wall, with its lead preferably routed and clipped along its length. RAILTRACK 15

18 Page 16 of 21 Withdrawn Document Extension leads should only be used, as a temporary expedient, when no suitable fixed outlet is available at the work location. Portable reel extension leads should not exceed 20m in length and should be fully unwound before use Extension leads should be appropriately rated for the application Extension leads should be suitable for the location in which they are to be used. Leads used in an industrial environment should be fitted with the correct coloured BS4343 plug and socket in accordance with the details above Extension leads should be routed or protected in such a manner so as not to cause a tripping or safety hazard Regular inspection should be carried out by a competent person, the periodicity will be dependent upon the usage, but 6 months is recommended Reference should be made to HSE Guidance Notes No GS37 and to HS(G) Tools and appliances Inspection hand lamps to BS Traditional tungsten filament bulb hand lamps should be 50V Alternatively a rough duty fluorescent hand lamp in a double insulated, high strength case to IP67 is available for 110V, centre tap earthed supplies may be used to avoid the provision of a 50V supply for hand lamps Reference should be made to the HSE Guidance Note PM Portable motor operated tools and appliances should comply with the of BS2754 and BS2769. If possible they should be of Class II (double insulated) construction. If it is not possible to obtain tools of Class II construction, tools of Class I or preferably of Class III construction should be used Non motor operated appliances Tools and appliances not covered by BS2769 should comply with the requirements of the appropriate British Standard. In the absence of a British Standard, a recognised equivalent standard should be used. Tools and appliances should be marked with the number of this equivalent standard Tools and appliances of double insulated construction should carry additionally the symbol for double insulation Except for tools and appliances of double insulated construction, the flexible cables should include a protective conductor to which all non-currentcarrying parts of the tool or appliance should be connected. 16 RAILTRACK

19 Page 17 of Flexible leads Heavy duty flexible cables of adequate rating should be used with all tools and appliances. The flexible cable should comply with BS6007 or BS In situations where it has been decided to supplement an RCD with earth core monitoring, and site conditions may give rise to excessive damage to the cable, consideration should be given to the use of copper braided cable Where copper braided cable is used, the braiding should be efficiently earthed but the braiding itself should not be the only earth connection for the metal of the tools/appliances. 10 Maintenance and testing 10.1 Maintenance procedures and periodicity - Maintenance and testing procedures and periodicity's should be determined for each installation to ensure safe and efficient operation throughout the designed life. These should take account of recommendations from equipment manufacturers and statements on inspection and testing within BS Documentation - Comprehensive records relating to design, commissioning and maintenance should be established and maintained. This includes "as installed" drawings and manuals Test equipment All test equipment and instruments used to verify performance and conformity with the installation specification should be calibrated in accordance with BS5781. Test equipment should be of suitable accuracy standards and fit for the purpose used Fused test leads should be used with instruments for measurements on equipment where there is a risk of contact with live conductors at or connected to mains power supplies Reference should be made to the HSE Guidance Note GS Auditing - A system of auditing should be established to ensure that maintenance is carried out as prescribed and that records are up to date. Historical records should be used to monitor equipment performance and reliability, and as a warning of deterioration or imminent failure. RAILTRACK 17

20 Page 18 of 21 Withdrawn Document Appendix A Approved suppliers of residual current devices for use in D.C. electrified areas A.1 A.2 Bennett (Electrical Engineering Ltd.) Blakley Electrics Ltd. 86 Downlands Road Tel: Conington Road Tel: Purley Lewisham Fax: SURREY CR2 4YN Fax: LONDON SE13 7LJ A.3 FDB Electrical Ltd. Tel: Reynard Mills Trading Estate Fax: Windmill Road Brentford MIDDLESEX TW8 9NZ 18 RAILTRACK

21 Page 19 of 21 Appendix B Typical circuit design record sheet Installation design criteria Circuit description No watts 1 Design current (I b ) = volts = = A 2Nominal current (I n ) determined by protective device = A Is discrimination with source achieved Y/N 3 Installation method - Table 4A = No 4 Ambient temp. correction factor (C a ) - Table 4C1/2 = Thermal insulation derating factor(c i ) -Table 52A = Grouping correction factor (C g ) - Table 4B1/2/3 = In Correction = = (I t ) = A Ca. Cg. Ci 5 Max permissible volt drop (4% - Vd in source) = V Actual volt drop = mv x Ib x m = V Selected cable size - Tables 4D1A to 4L4B = mm 2 Current carrying capacity = A 6 Earth loop impedance at circuit source (Z e ) = Ω Prospective short circuit current at protective device = A Max permissible earth loop impedance (ZS1) = Ω CPC size = mm 2 Earth loop impedance of circuit = Ω (Z e ) +{(R1+R2) x m } x (multiplier) = (ZS2) 2 I t 7 Thermal constraints S = = mm 2 K V I = ZS 2 = A t = time taken for protective device to break = s K = 115 (copper) or 51 (steel) 2 2 Energy let through K S = x = A 8 TN-C-S bonding conductor - Table 54H = mm 2 Note that the values for R1/R2 can be obtained from the IEE 16th edition Guidance Notes - Selection and Erection Tables G1/G2 or from cable manufacturers data sheets Cable selection - Type - Size : - PH mm 2 N mm 2 CPC mm 2 Protective device - Type - Rating Amps RCD required - Y/N if Y - Type Rating Amps Prepared by Checked Approved RAILTRACK 19

22 Page 20 of 21 Withdrawn Document References Reference documents. The following list of documents is for information only and should not be taken as complete and all-embracing. The Health & Safety at Work, etc. Act The Electricity Supply Regulations Fire Precautions Act - Sub-surface Railways The Electricity at Work Regulations HSE Guidance Notes: GS24 Electricity on Construction Sites GS27 Protection Against Electric Shock GS37 Flexible Leads, Plugs, Sockets, etc. GS38 Electrical Test Equipment for Use by Electricians HS(G)107 Maintaining Portable and Transportable Electrical Equipment PM29 Electrical Hazards from Steam/Water Pressure Cleaners, etc. PM32 Safe Use of Portable Electrical Apparatus PM38 Selection and Use of Electric Handlamps PM53 Emergency Private Generation: Electrical Safety British Standards BS88 Cartridge fuses for voltages up to and including 1000V A.C. and 1500V D.C. BS196 Spec. for protected-type non-reversible plugs, socket-outlets, cable-couplers, etc. with earthing contacts for single phase A.C. circuits up to 250V. BS1361 Specification for cartridge fuses for A.C. circuits in domestic and similar premises. BS1363 Specification for 13 A fused plugs and switched and unswitched socket outlets. BS2754 Construction of electrical equipment for protection against electric shock. BS2769 Hand-held electric motor-operated tools. BS3535 Isolating transformers and safety isolating transformers. BS3871 Miniature air-break circuit-breakers for A.C. circuits BS4343 Specification for industrial plugs, socket-outlets and couplers for A.C. and D.C. supplies. BS4533 Luminaires. BS5490 Specification for classification of degrees of protection provided by enclosures. BS5781 Measurement and calibration systems. BS6007 Specification for rubber-insulated cables for electric power and lighting. BS6500 Specification for insulated flexible cords and cables. BS7671 The Requirements for Electrical Installations Railway publications CP-PM-018 : Electricity supplies to Computers CP-PM-027 : Electric switch heating installations CP-PM-033 : Electric cable installations associated with P & M in BR Underground and other specified locations. CP-PM-040 : Provision of buffer stop lighting S-PM-446 Standard Specification: Electrical Distribution Installations S-PM-493 Standard Specification: Building Engineering Services - Electrical S-PM-494 Standard Specification: Building Engineering Services - Mechanical 20 RAILTRACK

23 Page 21 of 21 S-PM-585 Standard Specification: Shore based power supplies for traction and rolling stock: 850V A.C., single phase S-PM-586 Standard Specification: Shore based power supplies for traction and rolling stock: 415V A.C., three phase SP-PM-014 Contractors working on BR property and using mains operated portable and transportable electrical tools/appliances SP-PM-036 Electric Switch Heating: Standard layout of strip heaters SP-PM-042 Electric Switch Heating: Installation of electric strip heaters SP-PM-043 Electric Switch Heating: Safety precautions OM/008 Residual Current Devices (RCDs) for personnel protection: periodic testing of 20/30mA/30ms RCDs OM/062 Residual Current Devices (RCDs) for personnel protection: installation and siting of 20/30mA/30ms RCDs EHQ/SP/D/101 Earthing and Bonding for 50 Hz Single Phase A.C. Electrification. ECP183 for Ancillary Wiring of Electrical Distribution Equipment GM/RT1102 Normal & Standby Signalling Power Supplies. GO/ZT0113 Fire Safety Approval of Materials for use in Underground Stations GM/TT0264 Buried Electric Cables - Their Protection, Marking and Identification RAILTRACK 21