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Collection of standards in electronic format (PDF) 1. Copyright This standard is available to staff members of companies that have subscribed to the complete collection of SANS standards in accordance with a formal copyright agreement. The document may reside on a CENTRAL FILESERVER or INTRANET SYSTEM only. Unless specific permission has been granted, this document MAY NOT be sent or given to staff members from other companies. Doing so would constitute a VIOLATION of SABS copyright rules. 2. Indemnity Standards South Africa accepts no liability for any damage whatsoever that may result from the use of this material or the information contained therein, irrespective of the cause and quantum thererof. Click on one of the two boxes I agree with the above I do not agree

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Collection of standards in electronic format (PDF)

1. Copyright

This standard is available to staff members of companies that have subscribed to the complete collection of SANS standards in accordance with a formal copyright agreement. The document may reside on a CENTRAL FILESERVER or INTRANET SYSTEM only. Unless specific permission has been granted, this document MAY NOT be sent or given to staff members from other companies. Doing so would constitute a VIOLATION of SABS copyright rules.

2. Indemnity

Standards South Africa accepts no liability for any damage whatsoever that may result from the use of this material or the information contained therein, irrespective of the cause and quantum thererof.

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ICS 29.240.20

ISBN 0-626-15593-2

SANS 10198-8:2004 Edition 2

SOUTH AFRICAN NATIONAL STANDARD

The selection, handling and installation of electric power cables of rating not exceeding 33 kV

Part 8: Cable laying and installation Published by Standards South Africa

1 dr lategan road groenkloof private bag x191 pretoria 0001 tel: 012 428 7911 fax: 012 344 1568 international code + 27 12 www.stansa.co.za

© Standards South Africa

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SANS 10198-8:2004 Edition 2

Table of changes

Change No. Date Scope

Abstract Deals with the practical aspects of handling and installing cables. It covers the procedures to be followed when installing electric power cables by direct burial, in pipes under roads or railways, in air in cleats or hangers, on cable trays and in enclosed cableways.

Keywords cable laying, cable trays, cableways (electric), cleats, electric cables, installation, in-pipes installation, power cables.

Acknowledgement

Standards South Africa wishes to acknowledge the valuable assistance received from the

Association of Electric Cable Manufacturers of South Africa.

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SANS 10198-8:2004 Edition 2

Foreword This South African standard was approved by National Committee StanSA TC 66, Electric cables, in accordance with procedures of Standards South Africa, in compliance with annex 3 of the WTO/TBT agreement.

This edition cancels and replaces the first edition (SABS 0198-8:1988). SANS 10198 consists of the following parts, under the general title The selection, handling and installation of electric power cables of rating not exceeding 33 kV: Part 1: Definitions and statutory requirements.

Part 2: Selection of cable type and methods of installation.

Part 3: Earthing systems - General provisions.

Part 4: Current ratings.

Part 5: Determination of thermal and electrical resistivity of soil.

Part 6: Transportation and storage.

Part 7: Safety precautions.

Part 8: Cable laying and installation.

Part 9: Jointing and termination of extruded solid dielectric-insulated cables up to 3,3 kV.

Part 10: Jointing and termination of paper-insulated cables.

Part 11: Jointing and termination of screened polymeric-insulated cables.

Part 12: Installation of earthing system.

Part 13: Testing, commissioning and fault location.

Part 14: Installation of aerial bundled conductor (ABC) cables. NOTE The first five parts deal with factors to be taken into account when an electrical distribution system is being designed. The last nine parts deal with the practical aspects of handling and installing cables.

In South Africa the safety legislated requirements are defined (see 4.1) in the Occupational Health and Safety Act, 1993 (Act No. 85 of 1993).

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SANS 10198-8:2004 Edition 2

Contents Page

Abstract

Keywords

Acknowledgement

Foreword ... ............................................................................................................................................ 1

1 Scope ... ............................................................................................................................................. 3

2 Normative references ... ..................................................................................................................... 3

3 Definitions ... ...................................................................................................................................... 4 4 Installation by direct burial ... .............................................................................................................. 4

4.1 Trench excavation ... ............................................................................................................... 4 4.2 Depth of burial ... ..................................................................................................................... 4 4.3 Joint bays ... ............................................................................................................................ 4 4.4 Snaking of cables ... ................................................................................................................ 5 4.5 Trench bedding ... ................................................................................................................... 5 4.6 Pulling of cables ..................................................................................................................... 5 4.7 Installation of power cables close to other services ... .......................................................... 6 4.8 Backfilling ... ............................................................................................................................ 7 4.9 Jointing and termination ... ..................................................................................................... 7 4.10 Termination in a transformer ... ................................................................................................ 7

5 Installation in pipes under roadways, railways, etc. .. ...................................................................... 8

5.1 Type and size of pipe ... ............................................................................................................ 8 5.2 Installation of pipes ... ................................................................................................................. 8 5.3 Pulling cable into pipes or tunnels ... ......................................................................................... 9

6 Installation in air in cleats or hangers ... ............................................................................................ 9

6.1 Fully restrained system .............................................................................................................. 9 6.2 Unrestrained system ... .............................................................................................................. 9 6.3 Cleat spacing ... .......................................................................................................................... 9 6.4 Installation of single-core cables ... ........................................................................................... 9 6.5 Sun shielding ... ........................................................................................................................ 10

7 Installation on cable trays ... ............................................................................................................. 10

7.1 Erection of traywork ... .............................................................................................................. 10 7.2 Installation of cable ... ............................................................................................................... 11 7.3 Fixing the cable to the tray ... .................................................................................................. 11

8 Installation in enclosed cableways ... .............................................................................................. 11 Figures 1-7 ... .....................................................................................................................................12-18

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SANS 10198-8:2004 Edition 2

The selection, handling and installation of electric power cables of rating not exceeding 33 kV Part 8: Cable laying and installation

1 Scope This part of SANS 10198 covers the procedures to be followed when installing electric power cables by

direct burial, in pipes, in air, on cable trays and in enclosed cableways.

2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this part of SANS 10198. All standards are subject to revision and, since any reference to a standard is deemed to be a reference to the latest edition of that standard, parties to agreements based on this part of SANS 10198 are encouraged to take steps to ensure the use of the most recent editions of the standards indicated below. Information on currently valid national and international standards can be obtained from Standards South Africa.

SANS 533-1 (SABS 533-1), Black polyethylene pipes for the conveyance of liquids - Part 1: Low density black polyethylene pressure pipes.

SANS 559 (SABS 559), Vitrified clay sewer pipes and fittings.

SANS 677, Concrete non-pressure pipes.

SANS 791 (SABS 791), Unplasticized poly(vinyl chloride) (PVC-U) sewer and drain pipes and pipe

fittings.

SANS 921 (SABS 921), Pitch-impregnated fibre pipes and fittings and jointing.

SANS 966-1 (SABS 966-1), Components of pressure pipe systems - Part 1: Unplasticized

poly(vinyl chloride) (PVC-U) pressure pipe systems.

SANS 4427/ISO 4427 (SABS ISO 4427), Polyethylene (PE) pipes for water supply - Specifications.

SANS 10142-1, The wiring of premises - Part 1: Low voltage installations.

SANS 10198-1, The selection, handling and installation of electric power cables of rating not

exceeding 33 kV - Part 1: Definitions and statutory requirements.

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SANS 10198-8:2004 Edition 2 SANS 10198-2, The selection, handling and installation of electric power cables of rating not exceeding 33 kV - Part 2: Selection of cable type and methods of installation.

SANS 10198-4 (SABS 0198-4), The selection, handling and installation of electric power cables of

rating not exceeding 33 kV - Part 4: Current ratings.

SANS 10198-9 (SABS 0198-9), The selection, handling and installation of electric power cables of rating not exceeding 33 kV - Part 9: Jointing and termination of extruded solid dielectric-insulated cables.

SANS 10198-10 (SABS 0198-10), The selection, handling and installation of electric power cables of rating not exceeding 33 kV - Part 10: Jointing and termination of paper-insulated cables.

SANS 10198-11 (SABS 0198-11), The selection, handling and installation of electric power cables

of rating not exceeding 33 kV - Part 11: Jointing and termination of screened polymeric-insulated

cables.

3 Definitions For the purposes of this part of SANS 10198 the definitions given in SANS 10198-1 apply.

4 Installation by direct burial 4.1 Trench excavation Before excavating the trench, peg out the route and check to see that it agrees with that shown on the route drawings. To avoid damaging services, ensure that pegs used are not too long or driven too deeply. Dig trial holes to verify the positions of services and to ascertain whether support (in the form of sheeting and timbering) for the walls of the trench will be required. Where the depth of excavation exceeds 1,5 m, attention is drawn to the requirements (see foreword) that may require the trench to be shored. At all times, try to avoid damaging services or structures. When close to services, always use manual excavation, but in open areas where long lengths of cable have to be laid, mechanical excavation may be economical.

4.2 Depth of burial Normal depths of burial for cables covered by this standard are

a) 600/1 000 V : 500 mm

b) 1,9/3,3 kV and above : 800 mm both dimensions being from ground surface to the centre of the cable or group of cables. Excavate the trench to a depth greater than that applicable, to allow for bedding.

4.3 Joint bays Make each joint bay large enough to allow the jointer to work with as much freedom of movement and comfort as possible. Regard a length of 2 m and a width of 1 m as a minimum and make each joint bay 300 mm deeper than the depth of burial of the cable. Drape the sides of the bay with small tarpaulins or plastics sheeting to prevent loose earth from falling in during the jointing operation.

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4.4 Snaking of cables

Where practicable, snake the cables on either side of each joint position to relieve the joints of any thermomechanical stresses.

4.5 Trench bedding Where possible, lay cables on a bed of well-compacted sifted soil. If the soil taken from the trench is suitable, break it up and sift it through a sieve of maximum mesh size 12 mm; then ram it well down to provide a stone-free bed on which to lay the cables. Where the route lies in an area of made-up or aggressive ground containing rock, sharp stones, clinker, slag, mine sand or slimes, ash, bricks, etc., do not use this soil even if the particles are small enough to pass through a 12 mm sieve. For such sections, import loamy soil for use as bedding and covering. Sand that consists of spherical particles, obtained from a river bed or sea shore, is not suitable as its thermal resistivity is very high. Builders' sharp sand used in making concrete and which consists of irregularly shaped particles of different sizes can be used, provided that its thermal resistivity is low. Where site conditions warrant it, for example, in the case of a trench in rocky soil, it might be advisable to consider using a weak sand/cement mix as bedding and covering.

4.6 Pulling of cables 4.6.1 General

Certain insulation and sheathing material (e.g. PVC) become brittle at low temperature. To avoid damage, electric cables should not be installed, or removed from the drum when the temperature of the cable is below 10 °C.

Before installation, ensure that the drum or length of the cable has been maintained at a temperature exceeding 10 °C for at least 24 h, and ensure that the subsequent installation is carried out quickly, i.e. before the cable temperature is allowed to drop below 10 °C. A common method of increasing the temperature of a drum of cable is to strategically place lighted paraffin-operated danger lamps close to the open slats of a cable drum and to cover the arrangement with a tarpaulin sheet. After a period of 24 h, the cable is usually sufficiently warm to allow damage-free installation.

4.6.2 Direction of pulling In order to avoid unnecessary cross-overs in joints, it is important that each length of cable be pulled in the same direction. Cables are normally despatched ex-factory with the core sequence clockwise at the running end.

Before attempting to lay out the cable, remove the cover over the inner end and so cut the lashing that the end is free to move. Failure to do this will cause buckling of the cable. Take care to support the end as it works through the flange.

4.6.3 Direction of drum rotation

So arrange the drum that the cable leaves the top of the drum and the drum rotates in a direction opposite to that shown by the arrow that indicates the direction of rolling (see figure 1(a)). To minimize tension on the cable, particularly unarmoured or steel-tape-armoured cables, rotate the drum by hand and use a wooden plank as a brake to slow down or stop rotation as necessary. If the drum is allowed to continue turning when pulling has ceased, there is a danger of the cable kinking or twisting.

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4.6.4 Siting of drum If the cable has been ordered in specific lengths, so locate the drum near a joint position that the whole cable length can be paid out. Mount the drum on jacks as near to the trench as possible but far enough away to ensure that the weight of the drum will not cause the trench wall to collapse. Ensure that the spindle supporting the drum is horizontal. Carry out a check initially, and periodically during the payout, to ensure that the jacks are not sinking. If there is any doubt about the stability of the soil, mount the jacks on steel plates or railway sleepers in order to spread the load. Mount the drum at an angle of about 10° to 15° to the line of the trench, as shown in figure 1(b).

Before starting to pull a cable, check that the inner end of the cable has been cut free.

4.6.5 Skids and rollers

To assist the passage of the cable along the trench, the weight of the cable should be taken on rollers or skids. This is particularly important with heavy metal-sheathed cables.

Site the rollers on the bed of the trench at intervals of 3 m to 4 m, but close enough to prevent

undue sagging of the cable.

Place rollers or metal skids sideways at every change in direction to ensure that the cable keeps to a smooth curve and does not kink or twist. Avoid twisting the cable as it can result in "birdcaging" of the armour wires and tearing of insulation tapes of paper-insulated cables.

4.6.6 Paying out the cable

Position the leader of the pulling gang where he can see the majority of the route and can be seen and heard by the gang. Provided that the leader's calls are evenly timed and are taken up by the gang, and a series of co-ordinated even pulls are applied throughout the length of the cable, the cable will leave the drum smoothly. If a guide rope is required, attach it to the leading end of the cable by means of a cable stocking, never directly, such as to the plumbed cap of a paper-insulated cable.

Where more than one cable is to be laid in a trench, lift the first cable carefully off the rollers and lay it

to one side while the next cable is pulled in.

Specialized equipment and techniques are available for the mechanical pulling of cable. When the last cable has been pulled, lift it off the rollers and remove the rollers and skids. Then lift each cable in turn and lower it, working from one end, to locate it in its required position. If three single-core cables are to be laid in close trefoil, strap them together with cord or twine at 1 m intervals.

4.7 Installation of power cables close to other services 4.7.1 Cables laid alongside other services Where a power cable is laid alongside other services, allow as much clearance as possible to reduce the likelihood of damage to the other services during installation of the power cable, and to minimize danger to personnel during subsequent repair of, or alterations to, those services.

The requirements with regard to the installation of power cables alongside telecommunication

cables are as follows (see figure 2(a)):

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a) the clearance between power and telecommunication cables should be at least 600 mm, whether

or not the telecommunication cable is installed in a pipe; b) if the clearance is between 300 mm and 600 mm, provide reinforced concrete cover tiles or other suitable protection immediately above the power cable, or install the power cable in a pipe; and c) if for some reason, the minimum clearance of 300 mm cannot be provided, place concrete slabs or another suitable permanent separator vertically between the cables and provide reinforced concrete cover tiles or other suitable protection immediately above the power cable.

4.7.2 Cable crossing other services

Under normal circumstances, power cables are laid at a shallower depth than are water or drainage

pipes. Regard a vertical clearance of 300 mm between cables and other services as the minimum at a crossing, and provide some form of additional mechanical protection for the cable (see figure 2(b)). Use cover tiles or pipes for a distance of at least 1 m on either side of the crossing to reduce the likelihood of damage should access to the other service(s) be required at any time. A power cable is normally laid at a minimum depth of 300 mm below an existing telecommunication cable. Where a power cable is to cross either the proposed route of a telecommunication cable or an existing telecommunication cable, lay the power cable at such a depth as to provide a minimum of 300 mm vertical clearance and enclose it in a length of pipe at the crossing position or cover it with suitable tiles for a distance of at least 1 m on either side of the crossing. Do not regard plastics marker tape as providing sufficient protection in situations where it is likely that the area may later be re-excavated for the installation of other services.

4.8 Backfilling Before jointing is commenced, most of the cable trench should be backfilled. Tip sifted soil or specially selected sand into the trench and rake it smooth to cover the cable to a depth of 150 mm, then ram it well down by means of hand compacting tools. Do not use mechanical compactors at this stage. Backfill and consolidate all of the trench with the exception of the joint bays in this way. Where necessary, lay suitable cover tiles to cover the whole area in which cables are buried.

Where the excavated trench soil is suitable, replace and consolidate it (preferably using mechanical compactors) in layers of depth not exceeding 150 mm. If a marker tape is required, install it at a depth of about 200 mm below ground surface. At ground level, leave a crown of at least 50 mm tapering towards the edge of the trench to allow for subsidence. If wet or muddy soil is used for backfilling, further subsidence can be expected.

4.9 Jointing and termination Jointing and termination operations are detailed in SANS 10198-9, SANS 10198-10 and SANS 10198-11.

4.10 Termination in a transformer Where a direct-buried cable is terminated in a transformer, oil switch or other oil-filled apparatus having an oil containment pit, take precautions to ensure that oil leakage does not damage the cable. This can be achieved by making the cable enter the transformer pit via a pipe which is sealed at the bottom end into the wall of the pit as shown in figure 3.

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Seal the top end of the pipe with fibre cement, a suitable non-hardening putty or similar material, to

prevent the entry of water. Cleat the cable approximately 500 mm below the gland.

5 Installation in pipes under roadways, railways, etc.

5.1 Type and size of pipe (see also SANS 10198-2)

Table 1 lists pipes that are suitable for use as cable pipes under roadways, railways, etc.

Table 1 — Pipes for cables

1 2

Material of pipes Pipe specification

Concrete SANS 677 Earthenware (vitrified clay) SANS 559

Polyethylene SANS 4427 Polyethylene SANS 533-1 Unplasticized PVC (drain) SANS 791 Unplasticized PVC (irrigation) SANS 966-1 Pitch-impregnated fibre SANS 921

a Inside diameter. b Nominal outside diameter.

NOTE Ferrous pipes can also be used, but only for multicore cables.

3

Maximum diameter mm

a 100

b 150

a 150

The size of pipe used is normally 1,5 times the outside diameter of the cable, with a minimum clearance of 35 mm. Where three single-core cables are to be laid in one pipe, use a pipe having an inside diameter of about four times the outside diameter of the cable and draw all three in together. It is easier, however, to pull single-core cables into three separate non-ferrous pipes installed in close trefoil formation.

5.2 Installation of pipes Where possible, set cable pipes in concrete to anchor them in place and to ensure that they do not collapse in service. The axial separation of pipes set in concrete will depend on the space available, but ensure that it is at least equal to the cable spacing on the direct-buried sections. It is advisable to include a few spare pipes in any installation to avoid having to disturb the road or railway should it be necessary to lay further cables or to replace existing ones.

Where the length of the pipe run or the type of pipe or the cable finish warrant it, or at a change in direction, it might be necessary to construct draw-pits. It is advisable to pull a close-fitting mandrel through the pipe run on completion, to check that bore alignment has been maintained and to clear the pipe of any obstruction. Plug the ends of a pipe run temporarily to prevent the entry of stones and other foreign matter.

Provided that the length of the pipe run is less than 15 m, the laid-direct rating of the cable shall be used and the derating necessary for cables installed in pipes need not be applied. For this reason, it is advisable to complete the road or rail crossing by the shortest practicable route.

NOTE The SA Electrolytic Corrosion Committee recommends that any pipe that crosses a railway, extend 3 m

past each outer rail of each outermost track.

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5.3 Pulling cable into pipes or tunnels Where the cable is to be pulled into a long pipe run, set the cable drum up above one of the joint bays and feed the cable into the pipe in the way shown in figure 4. Do not pull the cable in an S formation (as shown dotted in figure 4) as there is a danger of kinking the cable. Pull the leading end of the cable by means of a stocking attached to a rope which has been threaded through the pipe, and pay the cable out carefully by rotating the drum to ensure that the cable does not kink at the entry to the pipe. The use of French chalk eases the drawing of cables into pipes.

If the pipe run is some distance from the cable drum, use guide rollers, as shown in figure 5, to

maintain a safe bending radius and to prevent damage to the cable sheath or the pipe entry. Use similar techniques for pulling cables into tunnels. After the installation of the cable, seal the pipe entries with non-hardening putty or fibre cement to prevent the entry of foreign matter.

6 Installation in air in cleats or hangers 6.1 Fully restrained system Where the "in air" section of a cable route is a very short length between two direct-buried sections, for example at a river or canal crossing, it is best to cleat the cable in such a way that all potential expansion and contraction is contained. Cleat the cable at intervals of 10D (where D is the overall diameter of the cable) to ensure that each section is stiff enough to prevent the cable from buckling between cleats under the action of the thermomechanical forces generated when the cable heats up on load.

6.2 Unrestrained system Install a complete "in air" system in such a way as to accommodate the thermal expansion and contraction of the cable. The simplest way to achieve this is to install the cable in cleats or in hangers and allowing it to sag between fixed positions to enable the cyclic expansion and contraction to take place uniformly along the whole length of the cable.

Where cables are fixed to a wall, allow a gap of at least 20 mm between the cable and the wall, for

free circulation of air.

6.3 Cleat spacing A cleat spacing of 3 m to 4 m may be used for both multicore and single-core cables. Install the cables with a sag of between 100 mm and 150 mm between cleats to allow for cyclic expansion and contraction of the cable.

6.4 Installation of single-core cables

Ensure that cleats used for single-core cables, whether installed in flat formation or in close trefoil formation, are non-magnetic. Such cleats are usually cast from a non-ferrous alloy. Unless the circuit is protected by fuses or other current-limiting devices, so install the cables that possible short-circuit forces (which would tend to make the cables fly apart) are contained. An economical method of installation is to cleat the cables in close trefoil every 3 m to 4 m, and to strap them at 1 m intervals on straight sections and 0,3 m on bends. Ensure that the intermediate straps are of non-magnetic material. Stainless steel straps, applied with a simple hand tool, have been found satisfactory for this purpose, but other non-magnetic or non-metal strapping may be used, provided it has sufficient strength and can withstand the corrosive effect of the atmosphere in which

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SANS 10198-8:2004 Edition 2 it is installed. Ensure that non-metal strapping has been suitably stabilized to minimize the effect of prolonged exposure to sunlight. Where stainless steel straps are used, do not apply them too tightly, and use a soft non-flammable material (such as woven asbestos tape) as a bedding.

The size of stainless steel straps necessary to contain system short-circuit forces depends on the

cable diameter and short-circuit current. Recommended minimum strap sizes are given in figure 6.

Where more than one cable per phase is required, install the cables in three-phase trefoil groups.

6.5 Sun shielding Cables installed outdoors shall be provided with shielding from the direct rays of the sun, otherwise considerable derating might be necessary. Where cast-metal cleats are bolted to steelwork that is unshielded from the sun, use wooden or similar blocks as packers to limit the heat conducted through the cleat to the cable sheath.

7 Installation on cable trays 7.1 Erection of traywork 7.1.1 Design considerations A cable tray can be free-standing, supported from a wall of a building or suspended from roof trusses or joists. When planning cable runs within buildings, ensure that the route does not interfere with pipework, ventilation ducting, etc. Take particular care when the cable tray is to be erected close to steam pipes, as the ambient air temperature surrounding even well-lagged steam pipes is likely to be appreciably higher than the design values assumed for the building as a whole.

7.1.2 Tray supports

Supports for a cable tray shall be fabricated from steel channel or angle, or built up from one of the proprietary support systems that are available. Supports made from the latter are more expensive in material cost but the overall installation cost might be lower, particularly if subsequent modifications have to be made. A variety of clips and clamps is available for securing tray supports to overhead steelwork.

Welding can be used with the approval of the building design engineer, but never drill structural steelwork. The spacing between supports will depend on the rigidity of the cable tray or ladder rack, and on the load to be carried. Use a spacing that is sufficiently close to enable a man to walk along the cable tray, and make the whole structure rigid enough to support a man on a ladder that is leaning against it.

7.1.3 Protective finish Ensure that a cable tray and all its supports are protected against corrosion. Ideally, hot-dipped galvanized steel should be used for both the tray and its supports, and a zinc-rich paint used on any cut or exposed surfaces. Other finishes such as epoxy-based paints have also proved satisfactory. In aggressive chemical atmospheres, it might be necessary to use a plastics-coated tray or even to employ an all-plastics material such as rigid PVC for the tray runs, with provision for frequent maintenance of the supports.

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7.1.4 Bends, tee-offs, etc. Where changes of direction or level are necessary or where a number of cables have to leave the main run, use properly engineered fittings or ensure that the cables are otherwise adequately supported.

7.1.5 Earthing

In order to comply with the provisions of SANS 10142-1, earth the cable tray and its supports at a sufficient number of points to ensure that the resistance from any point of the installation to the building earth does not exceed 0,2 Ω.

7.2 Installation of cable Where the tray is supported from a wall and has one edge open, the cable shall be laid out on the ground and lifted onto the tray. Where the tray is suspended, it will be necessary to thread the cable along the tray between the supports. If the route has many changes of direction, use a continuous pulling-in rope to which the cable is tied at frequent intervals. At each change of direction use helpers (seated on the tray) to guide the cable round the bends. When the cable reaches the far end of the route, remove the ties and pull in the next cable.

7.3 Fixing the cable to the tray When all the cables have been pulled in, attach each cable to the tray in the position shown on the tray fill drawing. (A tray fill drawing is a cross-section of the tray at a number of positions showing the relative position of each cable and detailing clearances required for the design rating.) It is not necessary to cleat multicore cables to the tray except at the ends of the route, but ensure that they are tied, at intervals of a few metres, with one of the plastics or metal clips available for this purpose, and are slightly snaked to allow for expansion. Where a group of three single-core cables is installed, cleat the cables in close trefoil at intervals of 3 m to 4 m and, to allow for cyclic

expansion and contraction, snake the cables alternately between the cleats (see figure 7). Use a minimum offset of 100 mm on either side of the centre-line, i.e. a tray of minimum width

(200 + 2D) mm, where D is the overall diameter of the cable. To contain possible short-circuit forces, strap the cables at 1 m intervals between cleats (see figure 6 for recommended sizes of straps).

8 Installation in enclosed cableways The method of installation to be used in enclosed cableways will depend on the cross-sectional dimensions of the cableway. It may be possible, if sufficient width is available, to install a number of cable trays on either wall, but allow enough space for a man to walk between the trays. The floor of the cableway may also be used, particularly for groups of three single-core cables, the cables being cleated and strapped as in 7.3. If there is insufficient space for cable trays, the cables shall be cleated in vertical formation, at 3 m to 4 m intervals, to the walls of the cableway, but only if a ventilation clearance of at least 20 mm is maintained between the cables and the wall. Wherever possible, use the minimum vertical clearances given in SANS 10198-4 to ensure adequate air flow and to make any further derating of the cables unnecessary. If three single-core cables are to be installed in vertical formation, cleat them. Do not lay them in J-hangers as there is a danger of the upper cables jumping out of their hangers if a short-circuit should occur.

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Figure 1(a) — Arrangement of drum

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Figure 1(b) — Drum and cable rollers

Figure 1 — Arrangement of drum and cable rollers

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Figure 2(a) — Power cable running parallel to telecommunication cable

Figure 2(b) — Power cable crossing other services

Figure 2 — Installation of power cables in proximity to other services

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Figure 3 — Cable entry into oil-filled apparatus

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Figure 4 — Cable fed via joint bay on long pipe run

Figure 5 — Guide rollers used at entry to pipe

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NOTE

a) Three single-core cables cleated in close trefoil at 3 m to 4 m intervals, with a sag of 100 mm to 150 mm between cleats. b) Strap spacing 1 m on straight sections, 0,3 m on bends.

Figure 6 — Recommended minimum size of non-magnetic stainless steel straps to be used to contain short-circuit forces

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Figure 7 — Cables snaked between cleats on cable tray or on floor of cableway

© Standards South Africa

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