Cable trays and ladder installation

I have uploaded a few pictures and a diagram on the installation of electrical cable trays and cable ladders for those who have some need for them. At the end of these pictures, you will also find a sample specification for the cable tray and cable ladder installations in multi-storey office buildings. If you wish to see more photos of electrical installations, this post, Free electric installation pictures.
Picture 1 – Cable tray at high level inside a chiller plant room



Cable trays for the installation of electric power cables are usually specified as perforated hot-dipped galvanized sheet steel.

The term perforated usually is defined as holes provided to the sheet of the trays to allow the movement of airflow that can provide a more natural flow of air circulation around the electric cables. This air movement can effectively help cool the cables on the tray.

All electric cables carrying current dissipate some power because of the resistance of the current carrying conductors.

If the energy dissipated in the form of heat is not carried away from the cables, the cables will heat themselves up and effectively operate at the higher temperature than the actual surrounding air. This will lower the actual maximum current that the cables can actually handle.

This IEE Regulation provides a table of current carrying capacities of cables that are run on perforated cable trays. However, these cable ratings are only applicable if the holes occupy at least 30 percent of the surface area of the trays.

You can also see from the picture that the cable trays are installed at the highest level, which is above all the pipe works in the plant room. This does not happen by chance.

Prior to commencement of the installation work, the construction people should prepare a coordination plan that incorporate all services and structures in a given area.

With all construction layouts of all building services superimposed into a coordinated layout, then the horizontal and vertical alignment of the pipe works, the cabling works and building elements (i.e. floor beams and columns) can be properly adjusted and tuned so that each element of the works will actually be able to be installed where it is supposed to.

For example, the electrical cable trays in the picture should not be installed below pipe works. The reason being there is always a chance throughout the life of the buildings that a pipe or joint will leak. If the pipe work is above the cable tray, then the water or other liquid in the pipe can drop onto the cables, eventually travel along the cable length, and enter the electrical switchboards. The will surely result in damages to the switchboards and the electrical components inside.

In addition to the damages, this situation will lead to hazards of electrical accidents. If there is a trunking or conduit works that are jointed to the trays or the switchboards, then the travel path may finally lead to some switched socket outlets or other fixed electrical equipment.

Serious electrical accidents may happen before the problem is actually noticed by anyone in the building.

The second main reason for having the coordinated services drawings are that different mechanical and electrical services are usually done by different trade sub-contractors. Each has their own schedule of work and priorities.

Without a prior coordinated construction plan available to each one of the trade subcontractors, the first teams that start the installation works at the area would surely choose the piping or cabling route that is most convenient or the most economical for them.

Then the teams that come in at later time will find that the route they need to run their services have been taken, or the path has been blocked. Relocation of the already installed works can cost a lot of money and abortive works, something all contractors would avoid as best as they can.

So many times the owner of an installation is handed over with installations that are badly coordinated. These sorts of substandard works can present not only hazards, but also costly to run and sometimes impossible to maintain and carry out service or repair works.

One of the major and most difficult tasks of a supervision engineer is to make sure that this aspect of work is properly taken care of.

The cable trays and the cable ladders, among other elements of an electrical installation, are the major components that need to be coordinated. This is because the large cables carried by these trays and ladders are usually difficult to zigzag around obstacles.

Picture 2 – Cable tray hanger system and angle bend piece



The picture shows a closer view of the angle piece of the cable tray. This is another important matter need attention of a supervision engineer during construction. Many clients and engineers do not accept the angle bends that are fabricated at site.

Cable tray systems are usually proprietary systems. The components are supplied in standard pieces, but most types of factory-made pieces are available nowadays. The contractors or installers do not need to do self-fabricated piece by modifying the factory-supplied standard piece.

Angle bends, the piece that is the 90-degree bend in the photograph above, cost money. They are generally more expensive than the straight run pieces. In large installations, many of the angle bend pieces are required. So there is always a tendency by the installers and contractors to modify and improvise using the lower cost straight run pieces instead of using factory-manufactured angle bends.

The problem with bends fabricated at site is control of workmanship. A badly fabricated angle bends (and other types of bends and accessories fabricated at the construction site) can cause serious damage to the cables during the cable installation works.

Many of these damages are difficult to spot and even the task of thorough inspection on the cables are difficult to be carried after the cables are installed in place on the cable trays and the cable ladders.

This is the main reason all non-standard pieces and accessories of a cable tray system and a cable ladder system should be factory-manufactured.

Picture 3 – A straight run cable tray under soffit of slab along a corridor



The above photo shows a stretch of the cable tray along a building corridor that uses only the standard pieces. The contractors have not much room to cut corners here. Not like the angles and bends that are necessary in congested spaces like the plant room in Picture 1 and Picture 2 above.

Picture 4 – Perforated cable tray with the circuit protective conductor (3 mm x 25 mm copper tape) installed




The above picture shows a stretch of vertically mounted cable tray. One or two readers may notice that this stretch is not painted like the others in Picture 1, 2 and 3. This one and those in the other pictures above are actually at the same building.

However, the one in Picture 4 is not painted because their materials and installation are covered by different specifications, which is the mechanical specification. It is going to carry electric cables for the chiller plant. That is why it is under mechanical specifications, and those specifications did not require them be painted.

Those in Picture 1, 2 and 3 are actually for electrical distribution cables and are under electrical works contract. The contract specification requires that all electrical trays, trunking and conduit be painted with orange color.

Picture 5 - Another air-cond cable tray



Cable Ladder

This section is about the installation of cable trays and cable ladders. However, I have spoken only about the cable trays.

Actually, the installation of cable trays and the cable ladders are about the same.

You can compare the installation from the pictures. (UPDATE: You can see the cable ladder pictures at this post, Electrical cable ladder pictures.)

For building constructions, the cable ladders are usually used for large plant room areas and where larges cables are used. The constructions of the cable ladders are better suited to handle the weight and stresses imposed by large cables.

One important point to note is that the cables mounted on cable ladders are just like cable installed in free air. If the cable trays have 30 holes occupying the surface of the tray, the cables on cable ladder are like installed in free air. The cooling qualities of this method of installation is better and therefore the cables can carry higher continuous current for a given size and type of cables.

Picture 6 – Diagram of the cable tray hanger



The mounting methods for cable trays and cable ladders are generally the same. This diagram shows some details on the type of materials and the method of fixing.


Sample specifications on installation of cable trays and cable ladders

A. Cable tray materials

a) Wherever cable trays are required for use in the contract works, the contractor shall supply and install perforated type, hot-dipped galvanized cable trays complete with all the necessary bends, tee pieces and adaptors where changes in the cable tray widths are required. The cable trays shall be of heavy-duty construction, made from sheet steel of 1.6 mm minimum thickness (for tray dimension of up to 300 mm width), and a minimum width of 2 mm for sizes above 300 mm width.

b) All fittings and accessories for the cable tray system including the tee pieces, bends, intersections and other accessories shall be factory-manufactured and purpose-made by the same manufactures. Custom-made fittings fabricated at the construction site will not be acceptable.

c) Depending on the installation situation, the cable trays may either be suspended from the underside of the floor slabs or roof structural works, supported on columns or walls, or installed on the floor. All materials for the suspension units, angle supports, structures etc shall be hot-dipped galvanized.

d) Cable tray supports, hangers and structures shall be spaced adequately apart to cater for the weights of the cables and the trays supported by them. Under no circumstances will the cable trays and the cables be permitted to sag. Any sag found on the installation works shall be repaired or replaced by the contractor at his own cost. The spacing of the support shall not exceed 1.2 m, and supports shall be provided not more than 150 mm away from any bend, tee, intersection or riser. The contractor shall be required to submit technical calculations to justify the structural integrity of the cable tray supports.

e) In cases where a single layers of cable trays is insufficient to accommodate the number of cables to be laid thereon, the contractor shall install two or more layers of cable trays on a common set of cable tray hangers. The supports or the structure shall be sufficiently robust and with sufficient capacity to cater the additional weights of the trays and the electrical cables.

f) Fixing clips or cleats for cables on the trays shall be fixed by means of non-corrosive metal screws (or bolts, washers and nuts).

g) All cable trays shall be installed with the greater dimension in the horizontal plane unless otherwise agreed by the Employer’s Representative.

h) The whole cable tray system shall be completely earthed with equipotential bonding conductors using 25 mm x 3 mm copper tapes. All connections between the copper conductors shall be accomplished using square copper clamps.

i) Provisions of the cable tray for the telecommunication systems shall be as per the tender drawings. The color of the paint applied s shall complied with the requirements of the telecommunication authority

j) For all other services, the painting shall be in the form of color bands of 50 mm width at 1.5 m interval, or a minimum of one bend per section.

B. Execution

a) All cable trays and cable ladders shall run vertically, horizontal or parallel with features of the building and in accordance with BS 7671. The contractor shall be responsible for coordinating them with other services during the installation works.

b) Galvanized coating damaged by excessively rough treatment during transit and erection shall be repaired using at least two coats of good quality zinc-rich paint complying with BS 4652.

c) The maximum size of damaged area for which such repairs are acceptable shall be in accordance with BS EN ISO 1461: 1999.

d) Cable trays and cable ladders shall not be cut at site. Instead, they shall be supplied in appropriate lengths from factory for assembly at site.

e) Splice connector plates shall be located according to manufacturer’s recommendation. Where necessary the trays and ladders shall be cut at site to suit splice locations.

f) The splice connector plates shall be located outside of tray side rails. The adjacent tray or ladder sections shall be bolted using nuts and washers, on the outer side of the tray. The torque nuts used shall be to manufacturer’s specified values.

g) Expansion splices shall be positioned properly with the connector fasteners securely locked to permit the tray or ladder to expand or contract freely.

h) Trays and ladders shall be securely anchored to supports. They shall be secured such that the tray or ladder system will not move during cable installation.

i) Holes shall be punched or drilled in the side rails or troughs only as needed for splicing of sections cut at site.

j) Where cables are to be installed across dividers, divider strip protectors shall be installed. Where cables are to pass over the tray edge, a sheath edge with compassable materials similar to the cable sheath shall be installed.
k) Holes for attachment of conduit to blind end-plates shall be punched at site.

l) All cable trays or cable ladders damaged during installation or cable pulling shall be restored to new condition or replaced.

m) Cable trays and ladders installed above piping and other obstructions shall meet the required headroom. The minimum clearance from the top of the tray side rails shall be 300 mm.

n) The side of the cable tray facing the wall shall have a clearance as per the manufacturer’s recommendation. The other side of the cable tray shall have a minimum clearance of 100 mm.

o) Bends, elbows, hinged splices, etc shall be of proprietary manufacture and shall not be fabricated at site.

C. Installation of supports for the cable trays and ladders

a) Horizontal and vertical supports shall provide at least 30 mm bearing length from each rail and shall have provisions for hold-down clamps and fasteners.

b) The side rail shall bear on the support. Where necessary, shims shall be used to elevate the trays or ladders and provide bottom clearance to the supports. The trays or ladders shall not bear on the support.

c) Vertical straight lengths shall be supported by wall-mounted brackets at intervals as dictated by building structure but this shall not exceed 1 meter.

d) Horizontal cable trays and ladders shall be supported by either wall mounted support bracket or a hanger rod system. The intervals between support shall be as recommended by the manufacturer but this shall not exceed 1 meter for wall mounted support brackets, and 1.2 meter for the hanger rod system.

e) The hanger rods shall be positioned and installed according to the manufacturer’s recommendation. The selection of the rod sizes shall be determined based on the total loading of the support system. The contractor shall be required to submit technical calculations to justify the structural integrity of the structural system of the cable trays and ladders.

f) Sloping trays and ladders shall be supported at intervals not exceeding those used for the horizontal trays and ladders of the same design.

g) Cable tray support shall be installed at each cable drop-out.

h) Cables shall be supported by proprietary make hanger system and cable clamps on the cable tray and ladder. Cable straps are not acceptable in this contract.

D. Installation of splice connectors

a) Splice connectors shall be located as recommended by the manufacturers.

b) Splice connectors shall be attached by round head bolts with the nuts and washers located on the outside of the tray or ladder.

c) Thermal expansion splices shall be installed wherever expansion joints occur.

d) Where space constraint demands, reducer plates shall be required. The structural straightness of the tray shall be maintained using supplementary permanent framing.

E. Installation of cable exits from cable trays and ladders

a) Conduits shall be attached to the side rail with conduit clamps and brackets. Holes shall not be made in side rail for conduit attachment.

b) The minimum bending radius of cable exit from trays or ladders shall be maintained using drop-out plates, vertical riser elbow fittings, or other accessories designed for control bending.

c) The edges and flanges of the cable trays and ladders at locations of cable exit from the trays shall be suitably sheathed to prevent injury to cable insulation.

F. Installation of divider strips

a) These divider strips shall be installed where different system wiring is installed in a common tray or where shown in the design drawings.

b) Divider strips shall be anchored to every ladder rung using fasteners, which attach to the tray without the need for drilling or punching at site.

c) The faster shall attach to the tray without the need for any drilling or punching of hole at site. The fasteners shall also present minimum exposure to the cables by having rounded exposed parts.

G. Installation of fire barriers and fireproof enclosure

a) Fire stop seals shall be provided where cable trays and ladders pass through floors or walls.

b) Fire stop installation shall as specified in the FIRESTOPS section.

c) For cable ladders and cable trays passing through the floor slabs and walls, the installation of fire stops shall only be carried out after the utility or services provider has completed their cabling works.

H. Earthing

a) All cable ladders, cable trays and interconnecting trunking and conduit shall be earthed as described in earlier paragraphs.

b) Earth links shall be used to electrically interconnect joined sections of the trunking, cable trays and the cable ladder system. The resistance measured between adjacent sections shall not exceed 0.01 ohms.

I. Handling, transport and storage

a) Conduits, trunking, cable trays, cable ladders, fittings and accessories shall be separately packed. They shall be delivered in appropriately labeled packing in accordance with the manufacturer’s recommendations. All articles shall be securely packed to prevent any movement and damage during transport. To avoid wet storage staining, transporting of galvanized articles shall avoid damp and/ or badly ventilated conditions.

b) The manufacturer shall provide information for unpacking and safe handling of all articles.

c) On arrival at site, the consignment shall be checked against the delivery notes.

d) All parts and components shall be stored indoor, in a clean, dry and well-ventilated place. Galvanized articles shall not be installed on clinches or ashes.

J. Tests

1) Type tests – Cable trays and ladders shall be type-tested to NEMA VEI standard as follows:
a) VE 1-3.01 Destruction load test
b) VE 1-3.02 Deflection test
c) VE 1-3.03 Electrical continuity of connections
d) Provide complete type test reports

2) Acceptance tests at Manufacturer’s Work

The cable trays, ladders, fittings and accessories shall be subjected to the following:

a) Visual inspection:

i) Correct type of cable trays and cable ladders
ii) Correct markings
iii) Dimension checks
iv) Damage on trays and ladders
v) Damage on galvanizing
vi) Fittings and accessories are of proprietary type.

b) Inspection and testing of galvanizing for compliance with BS EN ISO 1461: 1999

i) Determination of coating weight
ii) Uniformity of coating
iii) Deflection tests
iv) Electrical continuity of connection

c) Provide complete acceptance test reports

d) The manufacturer test shall be verified and witnessed by Employer’s Representative, or his representatives.

3) Inspection and testing at site:

a) Upon delivery to site, check the condition as follows:

i) Damage on the cable trays and ladders
ii) Damage on galvanizing
iii) Fittings and accessories are of proprietary make
iv) Store indoor

b) Repair or replace damaged parts or damaged galvanized coating areas.

c) Upon completion of the installation, visual inspection and verification of:

i) Correctness of location and mounting
ii) Labeling and marking
iii) Damage on the cable trays and ladders or their accessories
iv) Damage on galvanizing
v) Earthing of the cable trays and ladder system



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PVC PILC XLPE MICC cable installation

The following sample specifications covers the installation of PVC, XLPE, PILC and MICC cables in a new high-rise office building.

Photo 1 – Electric cables installed on cable tray


UPDATE March 18, 2011: As part of the re-construction process of this blog, I will gradually upload photographs of real installations of electrical works.

The photos will be attached to the relevant existing posts when that is possible.

If the original article is in the form of specifications like the one below, having pictures and images in the middle of it may spoil the structure of the article. In that case I may send a new post to load the photographs.

Then I will create a hyperlink in the existing post to connect to the new post and the photos.

Of course the new post will also be hyperlinked back to the original post so the readers will not lose their way trying to come back to the article he/she was previously reading.

The uploading takes time and I will do it gradually. In the process, the article will look half-completed and definitely not nice-looking.

However, I set up this blog to give readers contents. Lots of contents. If you are looking for a nice-looking blog, this is definitely not a right place.

SCOPE
The scope of this section is to set out the materials, requirements, methods, workmanship, standards and regulations in connection with the cable installation works.

TYPE OF CABLES
PVC insulated armored cables (PVC/SWA/PVC)
Cables shall be PVC insulated, steel wire armored, PVC sheathed overall and shall be manufactured and tested in accordance to the specifications of BS 6346. They shall be of the 600/1000 volts grade with high conductivity copper conductor.

XLPE insulated cables
Cross-linked polyethylene insulated cables shall be suitable for 1000 volts with high conductivity copper conductor. They shall be manufactured and tested in accordance with to the specifications of B.S. 5467.

For 11000/ 33000 volts applications, the cable shall be manufactured and tested according to the specifications of B.S. 6622:1985.

For normal operation, XLPE insulated PVC sheathed (XLPE/PVC) cables shall be employed. For underground applications XLPE insulated, steel wire armored, PVC sheathed (XLPE/SWA/PVC) cables shall be used.

Paper insulated cables
The manufacturing of mass-impregnated, non-draining type paper-insulated and lead-alloy sheathed (PILC) cables shall fully comply with the requirements of BS 6480. Unless otherwise specified, PILC cables shall be insulated for 1000 volts with high conductivity copper conductor.

For underground distribution, PILC cables with steel tape armored and served overall (PILCSTA&S) shall be employed.

Mineral insulated cables
Mineral insulated copper sheathed (MICC) cables shall be manufactured and tested in accordance to BS 6207 and shall be of the heavy-duty type of 1000 volts. The cables consist of high conductivity copper conductors, embedded in pressure packed magnesium oxide insulation within a robust, ductile, seamless copper sheath.

For situations corrosive to copper and underground installation, MICC cable with PVC sheath shall be used.

CABLE HANDLING
The most important point to observe in handling cables is that great care must be exercised at all times.
Every precaution should be taken to avoid dropping a drum of cables. Dropping, even from a short height, will flatten the layers of cable nearest to the barrel of the drum due to the weight from the outer layers. Similar distortion will also occur if the drum falls on its sides.

When rolling the drum into position it is essential that the drum rolls smoothly in the direction of the arrow painted on the side of the drum. If this instruction is not followed, slack cables will tend to accumulate towards the inner turns and may result in damages to the cables.

Wooden battens around the cable drum should be very carefully removed. Suitable tools should be used for this purpose.

When a drum is in position, it should be mounted on jacks and disposed so that the cable is pulled off from the bottom and not over the top.

It is preferable to mount the drum at one end of the cable run as close as possible to the edge of the cable trench so that the cable can be pulled off in a continuous manner on rollers in trench and is in its final position when the last turn leaves the drum. This procedure is not always possible because of the excessive length and weight of the cable run or because of obstruction or pipes under which the cables have to be threaded.

In such cases it may be necessary to position the drum at some other point along the cable run and lay off the cable on the ground near the drum in a series of loops, one above the other in the form of a figure eight, crossing the cable back and forth on itself.

When the whole length has thus been removed from the drum the inside end of the cable will be on top and can be pulled along towards its final position on rollers in the same manner as if the cable was coming off the drum itself. Whichever procedure is adopted great care must be taken at all times to ensure that cable is not twisted and that the turns are well above the minimum bending radii of cable. The radii of cable below 22 kV may be taken as follows:

For sizes up to 50 mm overall diameter – Min bending radii: 12 x diameter
For sizes 50 mm and above overall – Min bending radii: 20 x diameter

Wire cable stockings with an eye at one end should always be used with pulling ropes. Ropes should never be tied directly to the cable ends.

RE-DRUMMING OF CABLES
Owing to deterioration of cable drums, it is sometimes necessary to transfer cables to another drum. Steps to do this should be taken immediately when signs of the drum deterioration become evident and on no account must the transfer be delayed until the drum is on the point of collapse as so often happens.

Both drums should be jacked off the ground and the cable slowly wound from one drum to the other with the cable bending in the same direction on the new drum as on the old one.

Great care must be taken to ensure that the radius of the new drum barrel is not less than the minimum bending radius of the cable. As arrow should be painted on the side of the new drum to indicate the direction in which the drum was turned during rewinding operations i.e. the direction in which the drum should be rolled. The words “REWOUND CABLE” should also be clearly painted in Red on both sides of the drums.

The re-drumming of cables will only be carried out under the direct supervision of the S.O.’s Representative.

INSTALLATION OF CABLES

General
All cables shall be terminated in cable boxes or sockets of suitable size for the cable employed without excessive clearance.
The spacing of the cable supports shall be determined by the size of cable and in the case of cables of less than 25 mm in overall diameter the spacing shall not exceed 760 mm.

All cables shall be supported in such a manner as to unsure that they do not sag after erection and their means of support shall be to the approval of the S.O.’s Representative. Fixing shall be made with raw bolts or other patent fixing devise of design approved by the S.O.’s Representative.

Where cables enter or leave cable pipes or ducts, the entries shall be sealed effectively by means of close fitting solognum impregnated split wooden plugs and a mixture of compound and transformer oil or other approved method in order to prevent the ingress of water or dirt.

All cables passing through interior walls or floors shall be sealed effectively to the approval of the S.O.’s Representative by means of asbestos cement after the cables have been pulled through in order to prevent accumulation of moisture and the ingress of debris, sand and vermin.

All cables shall, where they pass through floors or otherwise in such positions vulnerable to damage by mechanical or other means shall be protected by short length of steel pipe suitable bushed to prevent abrasion of the cable.

Straight and tee joints
Straight and tee joints in any of the cables installed under this contract will only be permitted in very exceptional circumstances and only with the S.O.’s Representative approval in writing. The cost of such straight and tee joints, if permitted by the S.O.’s Representative shall be born by the contractor unless such joints are arising from unavoidable limitations in manufacturing lengths or from alterations in routes after initial approval.

Cable pulling
Winching of cables through ducts shall only be carried out with the approval of the S.O.’s Representative in which event a pulling eye shall be attached to the conductors.

A cable sheath stocking may be employed on cables where undue stress in the sheath is likely to occur.

Underground cable boxes
Straight through and tee underground joint boxes shall comprise a good quality, cast iron, split type box complete with nuts and bolts and accommodating a lead sleeve or case suitable for plumbing to the cable sheath. Boxes shall be free from blowholes and provided with compound filling holes and plugs. Internal and external box surfaces shall be painted with an approved preservative compound.

Boxes shall be provided with armor clamps and provision shall be made for bonding the steel wire armoring across the joint and on to the lead sheath or case. The bond shall comprise a tinned copper conductor and in no case shall it have a cross section area less than that of the largest conductor.

Lead sleeves shall be formed from solid drawn tubes and lead cases for three and four way joints shall be made from lead sheet halves rebetted and soldered together on completion of the joint. Lead sleeves and case shall be free from porosity and impurities, of adequate thickness, complete with filling holes and lead seals.

Core numbers printed on papers shall be strictly observed when jointing and such numbers shall be maintained throughout the system. Papers numbered ‘0’, ‘1’, ‘2’, and ‘3’ shall be identified as neutral, red, yellow and blue phases respectively and in the case of two core cables number ‘1’ shall be the phase conductor and ‘0’ the neutral.

Crossing of cores in boxes shall be avoided wherever possible but connections shall be consistent with the foregoing requirements.

Sealing end boxes
Box shall be of the split type with effectively sealed joint surfaces and manufactured from good quality cast iron free from blow holes with screwed plug filling and venting holes of ample dimensions and of such design as to permit continuous filling in one operation in order to avoid the formation of voids.

Box shall be painted internally and externally with an approved preservative compound and shall be complete with brass cone shaped wiping gland, armor clamp, fixing lugs and earth continuity bond across the box from armor clamp to equipment frame.

The top plate shall be tapped for conduit entry or fitted with bushing insulators as appropriate to the situations.
Where means of cable support is not provided within the equipment, or in any situation, the contractor shall provide adequate cable support below the sealing box in order to relieve the joint and the box of stress.

Where it is not possible to fix cable to the framework or supporting members specifically supplied for the purpose in or on apparatus, then the contractor shall supply and install to the satisfaction of the S.O.’s Representative such support fabricated from galvanized steels as may be necessary.

Boxes shall be of such design that they are suitable for attachment to the equipment served and shall allow cable conductors to be formed into the equipment terminals without distortion.

PVC or XLPE insulated armored cables

Jointing of PVC/SWA/PVC or XLPE/SWA/PVC cables shall be carried out by accredited and fully experienced jointers and evidence of this shall be produced to the satisfaction of the S.O.’s Representative before jointing is started.

All terminal sealing boxes, cable cores shall be carried through unbroken to apparatus terminals and cores shall sweat solid where they pass through cast resin.

All joint boxes, jointing materials and tools shall be of the type recommended ans manufactured by the cable supplier.
All joints which are buried in the ground shall be compound filled. The design of the box and the composition shall provide an effective seal to prevent moisture gaining access to the conductor ferrules and armor clamps.

Provisions shall be made for earthing the wire armor to the main electrode at the supply and by means of a metallic bond of adequate conductance, and the bonding connection should be as short and straight as possible.

The wire armoring shall be maintained electrically continuous and careful attention shall be paid to the design of all bonding clamps in joints and terminations to ensure that the resistance across a clamp is not higher than that of the equivalent length of the complete wire armor of the cable.

The conductance of the carcase of cast iron is normally sufficient for this purpose but, where it falls short, an auxiliary metallic bond shall be included.

Compression type glands for the terminations of cables will normally be included with the terminating boxes. Marshalling and other terminating boxes supplied under this contract, however, shall include the terminating cable glands.

The design of compression glands shall be such that the cable is not twisted when the gland is tightened. They shall provide facilities for the efficient bonding and termination of the armor wires and shall project at least 20 mm into the terminating box so that any condensation collected on the inner surfaces of the boxes cannot flow down between the cable cores. Where anti-condensation heaters are not fitted, drain holes shall be provided. It is possible to erect and dismantle any cable compression gland without the use of special tools.

Paper insulated cables
Jointing of PILC cables shall be undertaken only by by an accredited and fully experienced jointer and evidence of this shall be produced to the satisfaction of the S.O.’s representative before jointing is started.

At terminal sealing boxes, cable cores shall be carried through unbroken to terminal apparatus.

Every cable joint shall be started and finished during the same day and whenever cables are to be joined in the open during wet weather conditions, suitable precautions shall be taken to preclude ingress of moisture into the cable joint.

Joint and sealing boxes shall be thoroughly flame warmed on the outside of the box before pouring compound and compound temperature shall be checked frequently by the use of a suitable scaled and protected thermometer to ensure that the pouring temperature does not exceed the manufacturer’s recommendations and that overheating does not occur.

Whenever PILC cable is cut during the course of insulation, the open ends shall be sealed immediately, unless jointing is to follow, by means of a lead cap wiped to the sheath to form an air tight seal. Under no circumstances should PILC cables be sealed with insulating tapes.

PILC cables must be tested for moisture before jointing is commenced. Samples of paper both from the layers nearest to and furthest from the conductor should be immersed in transformer oil or paraffin wax, this will be immediately detected by bubbling. Samples of paper should be tested singly and should not be touched by hand but gripped in a pair of tweezers.

Testing of insulation resistance
An insulation resistance test should be made to each length of cable laid before jointing is commenced.

MICC cables
Insulation and continuity tests shall be carried out before and after MICC cable is installed using a 500 volt “megger” and this must result in an “infinity” reading, no lower value will be accepted. A blow lamp may be used for drying out cut cable ends if it is impracticable to cut to waste in which event the cable should be brought to cherry red heat at about 600 mm from the end and moisture carefully driven towards the cut end.

Minimum bending radius shall not be less than six times the cable diameter and saddle spacing not less than 60 times the cable diameter and nor greater than 760 mm whichever is the less.

An unsupported loop shall be left in the cable at terminations subject to vibration.

It is essential that the greatest care shall be taken to ensure that hands and all materials, particularly the compound are perfectly dry and clean when terminating MICC cables. The length of tails shall be kept to a minimum.

Dirt and metallic particles in the compound and any loose traces of dielectric left at the face of the sheath after stripping shall be carefully removed, prior to sealing.

Cold sealing compound shall be forced down one side of the pot and up the other at the same time “overfilling” in order to avoid trapping air at the base of the pot and to ensure that when the sealing disc is entered before crimping a completely solid insulation barrier is effected.

Electricians employed on termination of MICC cables shall be fully instructed and experienced in the stages of the operation and work will be stopped, if in the opinion of the S.O.’s Representative insufficient care and/or skill is not being exercised particularly in this phase of the work.

TESTING
The contractor shall be responsible for the testing of the cables and certifying that they are safe before the supply is switched on. Tests shall include continuity, phasing out and insulation resistance between conductors and between conductors and sheath employing 500 volts “megger” tester of other approved type tester. Voltage tests to prove the soundness of the protective servicing and continuity test to prove the soundness of the wire armoring. A copy of test results shall be submitted to the S.O. before the cables are energized.

FIRE RESISTANT CABLES AND INSTALLATION
Fire resistant cables shall be of 300/500 volts and 600/1000 volts and suitable for surface wiring and installation in conduit or duct.

Cables shall both fire resistant and flame retardant to IEC 331 and IEC 332 respectively. The cables shall also be tested for resistance to fire and water and mechanical shock to categories C, W and Z of BS 6387. The outer sheath shall be halogen free under IEC 754 Part 1. Test certificates to substantiate the compliance shall be submitted.

Cables shall be made of stranded, soft annealed copper conductor to IEC 228, mica tape fire barrier, insulation of cross-linked polyethylene with continuous conductor temperature of 90 degree Centigrade conforming to IEC 502 and outer sheath made of flame retardant low smoke and non-halogen polyethylene. Core identification of cable shall be by color of the insulation according to IEC 502. The maximum resistance of the conductors at 20 degree Centigrade shall not exceed that specified in IEC 228. The cables shall be FUJIKURA brand or equivalent.

Cables shall be suitable for installation by conventional methods without requiring expensive tools, seals or terminations. The accessories shall be non-hygroscopic, maintenance free and insensitive to vibrations. When installed on the cable trays, the spacing of saddles and the arrangement of cables shall be in accordance with the relevant BS or IEC standards. Minimum bending radius shall not be less than 6 times of the outer diameter of the cables.

The cables shall comply fully with the requirements of the Fire Department and relevant approval letter shall be submitted.
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