MOS of Cable Laying
1. Preparation
1.1 Drum Inspection and Mounting
Prior to installation, the cable drum should be visually inspected for damage, which may have
occurred during transport. The manufacturer’s seal on the inner and outer cable ends should be
examined and the condition of the sheath inspected for mechanical damage. If the cable is found
defective it shall not be installed and the cable shall be returned to the supplier for replacement.
During installation the cable should be carefully examined for any sign of damage as it leaves the
drum. This is particularly important on the outer layers, where drum batten nails can cause damage.
If it is necessary to roll the cable drum, it should be rolled in the direction indicated by the arrow on
the drum.
The drum should be mounted on jacks, cable trailer or cable stands. The cable can be rolled or pulled
off the drum as indicated on the outside of the flange. Lighter cables may be laid by mounting the
cable drum on its side on a truck-mounted turntable and laying the cable directly into the trench.
When pulling from large drums, i.e. over 2m in diameter, the cable should be supported to prevent
stressing the cable, from the drum to the trench on a suitable ramp.
Alternatively, cables can be rolled directly into a trench from the drum mounted on an excavator
moving along the trench.
To limit the chance of damage to the cable prior to removing the cable drum battens, a check should
be done to ensure that the drum-spindle is level and permits even rotation of the drum.
During pulling there is a tendency for cable slack to accumulate on the drum. Slack shall be avoided
and one possible method to achieve this is to limit drum rotation by using plank brake shoes against
one or both flanges of the drum. If the inner end of the cable on the drum, referred to as the ”Z” end,
protrudes through the side of the drum, then it should be watched during pulling to ensure it is not
damaged. It is advisable to tie a rope to the Z end, and pull through any slack cable that appears.
Pulling through Z end prevents buckling, and possible damage to the inner coils on the drum.
1.2 Cable Drums – Handling and Positioning
When handling drums, suitable precautions should be taken to avoid damage to the cable and injury to
people. Due regard should be paid to the mass of the drum, the method and direction of rolling and the
method of lifting.
It is preferable for ease of handling and safety to move drums by special cable drum trailers and
whenever possible the cable should be laid direct from these. In certain cases, it may be possible to
lay cable from a drum trailer whilst it is being towed alongside the trench, thus giving a considerable
saving in time and effort.
The drum mounting position, if stationary, will be influenced by the following:
Accessibility - Good access to where the cable drum is to be mounted.
Gradient - On sloping ground, cables should be pulled downhill.
Bends - The drum should be mounted at the end of the trench nearest the bends. The
force required to pull cable is less near to the drum, and therefore, the side forces and
friction on the bends will also be less.
Ducts - To minimize the disturbance to ducts and the resulting possibility of damage
to the cables, the drum should be at the end of the trench farthest from the ducts.
Jointing - Consecutive lengths of cable should be laid 'A' end to 'Z' end to ensure
correct rotation of the cores when jointing.
Generally, more than one of the above factors will be present and a compromise will be necessary.
When bends and ducts are adjacent the guidance given for bends applies.
When rolling drums, it should be over short distances only and the drum rotation should always be
according to the arrow marked on the drum flange. This will ensure that any slack cable is worked to
the outer end. Failure to take this precaution may result in slack cable collecting at the hub of the
drum causing damage.
The cable drum shall never be left unchecked, in case it rolls either by accident or vandalism.
Cable drums should be transported with the drum axis horizontal and any drum movement should be
avoided.
The cable drum must be so arranged that the cable be pulled off the top of the drum. If battens are
fitted and the end of the cable cannot be seen, the drum should be set up so that it will rotate during
cable laying in the opposite direction to the 'rolling' arrow.
Cable ends should be firmly attached to the drum during transport and storage to prevent damage to
the cable.
Care should be taken to avoid damage to the cables caused by nails or staples used in drum
manufacture or when applying battens.
For loading and unloading of cable drums, suitable lifting and hoisting equipment should be used. A
drum should not be dropped.
1.3 Winch - Positioning
Normally, the cable will be pulled direct from the drum trailer but in its absence, drum jacks and
spindles should be used. A 2.1m long by 75mm outside diameter 5000kg SWL high tensile seamless
steel tubular drum spindle with 2 x 5000kg ratchet type cable drum jacks with timber bases and cups
to take up to 100mm spindles will support cable drums holding up to 250m of the largest standard
sizes of LV, HV and EHV cables.
Cable drum jacks should be mounted on a firm level base. If the ground is uneven, a foundation
should be provided by using stout timber solidly packed.
Timber packing may also be necessary to prevent settling of the jacks by spreading the weight if the
ground is soft. It may be necessary to locate the drum in the roadway away from the trench and in this
case the drum should then be offset by not more than 30 degrees to the line of the trench. For safety,
the drum should not be mounted closer than 1m to trench excavations of normal depth.
The drum should be raised to just clear the ground and the drum spindle levelled to prevent the drum
moving to one end. The level of the drum should be checked by a plumb bob against the drum side or
by placing a spirit level on the drum spindle. When using a spirit level with heavy cable drums,
readings should be taken at each end to compensate for deflection of the loaded spindle.
The spindle should be greased and a check made for smooth rotation of the drum.
Drum battens and steel bands if fitted may then be removed. For safety, all nails should be withdrawn
from the battens and drum rim immediately and the battens stacked neatly.
The winch to be used may be of the platform mounted, trailer mounted, or vehicle mounted type.
The winch should be positioned at the end of the cable trench and securely anchored. It is important to
note that where a boom is used, the main anchorage against the pull must be at the lower end of the
boom. The anchorage should be obtained by cross bracings recessed into the sides of the trench.
2. Cable Pulling
Cable should always be pulled to provide a 1.2m overlap for jointing purposes. Where cable
is cut to length the end must be sealed to prevent moisture ingress.
2.1 Cable Attachments
When using Triplex cable, it helps to prevent the unwinding of the cable if 13mm wide cable
ties are placed on the leading 5m to 7m of cable, prior to the cable being laid. If this cable is
then to be pulled into ducts the cable ties should be taped over with Scotch 88 tape to prevent
the cable ties snagging on the ducts. All short lengths of triplex should be cable tied to
prevent the cable unwinding, prior to the laying of the short length of cable.
2.1.1 Attachment of Cable Stocking to Cable
The approved method of attachment of the cable pulling rope to the cable is by cable stocking
or three in one swivel head. There are wide ranges of sizes available from many different
manufacturers. The stockings distribute the pull and avoid damage; care must be taken to
ensure that the stocking fits over the oversheath of the cable. In the case of Triplex cable
individual stockings should be applied to all three cores and these in turn should be attaches
to the swivel on the pulling bond. In all cases the stocking should be pushed fully on to the
cable and should be secured at the end with binding wire as shown in the below figure. The
cable stocking will also have a SWL equivalent to the maximum pulling tension of the cable.
After the end of the cable has been freed from the drum the cable stocking should be fitted.
The below table gives guidance on maximum pulling tensions and diameters of cables most
commonly used.
2.1.2 Attachment of Pulling Rope to Cable Stocking
When pulling by winch, a clevis-ended swivel must be fitted between the rope and the
thimble of the cable stocking. The swivel, as shown in the above, is streamlined and complete
with clevis fittings for rope and stocking. It shall also have a SWL, which will at least match
the maximum pulling tension associated with the cable to be installed.
The swivel allows the rope to turn freely. Without a swivel a twisting strain will result under
load, and should there be a sudden release of this, the whip-back on a steel rope will be
dangerous and, in many cases, cause kinking.
2.1.3 Rope Bonds
The preferred rope bond used is steel wire rope, but this is not suitable for hand pulling as it
is springy, too small in diameter to grip, and broken strands may lead to injury.
When pulling by hand, either natural or synthetic fibre rope may be used but care must be
taken to ensure the SWL of the rope is not a limitation when pulling cables to the
recommended maximum tensions.
2.2 Methods
Winch pulling or the laying of cable direct from a moving cable drum trailer is to be
preferred to hand pulling purely because it is less arduous and fewer people are required.
Nevertheless, for short lengths of cable, hand pulling may be expedient. Whichever method is
used all men should wear protective gloves and footwear throughout the pulling/handling
operations.
2.2.1 Winch Pulling
The winch operating procedures outlined in these sections are suitable for most types of
winch at present available, although some variation in procedure may be required for a
particular type of winch.
Winches should be fitted with a digital dynamometer arrangement to ensure the maximum
pulling tension of the cable being installed is not exceeded.
The number of men required is dependent on the winch type and size, and the nature of the
job.
The person-in-charge should ensure that all personnel employed on cable winching are
familiar with the signaling procedures employed. Each signal should be positive and distinct.
Portable radio may be helpful on schemes where hand signals cannot easily be used.
At any time, any man in the team is at liberty to give the emergency stop signal should
personal danger or serious circumstances arise.
2.2.2 Laying Cable from a Moving Drum Trailer
Laying the cable directly into or beside the trench from a drum trailer whilst it is being towed
along slowly can make considerable saving in time and effort. This method can only be used
if there is unobstructed access beside the trench and if there were no pipes or services
crossing the trench under which the cable would have to be laid. It is ideally suited to
coordinated mains laying in a common trench.
When laying direct into a trench, the end of the cable should be fed off the drum and laid in
position in the trench. The drum trailer should then be towed slowly alongside the trench.
Three or four men must initially hold back the cable and then progressively ease it over the
edge and onto the trench bed.
If the trench edge is not firm enough to allow a vehicle to be driven reasonably close to it, the
cable can be fed from the drum trailer on to the ground beside the trench. The cable end is
pulled from the trailer and placed in its final position in the trench. The remainder of the
cable is then laid from the moving drum trailer directly on to the ground beside the trench.
Subsequently the cable is manhandled on to the trench bed, starting from the point where the
end of the cable is already in the trench.
2.2.3 Pulling in by Hand
When it is necessary to pull in by hand, the men should be spaced clear of each other along
the pulling rope. As the cable is pulled into the trench the men should move back from the
rope on to the cable.
To avoid dangers from trapping, men should not be positioned on corners, or on the drum
side of the cable rollers for pulling cable. The cable itself should be handled with cable slings
thereby avoiding the possibility pinching fingers between cable rollers and the cable, and
enabling men to pull with a straight back.
Care should be taken at bends to congregate men on the approach side so as to relieve friction
on the bend.
The supervisor should ensure good control of the cable and unified pulling efforts either by
using a whistle or other means with which the staff are familiar. Similarly, cessation of pull
should follow a clear signal.
It must also be seen to that any undue slack does not accumulate on the drum, by employing
somebody to apply braking, via the drum flanges, when necessary.
Where a cable is drawn through a road-crossing duct, pulling in should be stopped when the
cable end is near the duct mouth and the pulling in rope attached to a pilot rope or wire,
which has been previously drawn into the duct. The cable end should then be eased into the
duct mouth and pulling continued.
2.3 Flaking and Coiling Cable
As it is not always possible to lay the complete length of cable directly into the trench due to
obstructions, limited choice of drum mounting position, or the need to excavate and backfill
part of the trench quickly and as a result it may be necessary to coil the remainder of the
cable or flake it off the drum.
At all stages of these operations, care must be taken not to twist the cable or bend it too
sharply.
In the coiling method, few men are required as the cable has already been pulled off the drum
and the coils have merely to be handled individually into position, where they require little
space.
The flaking method requires more labor as the cable has to be pulled off the drum and
handled in figures of eight which are larger than coils and require more space.
2.3.1 Coiling Cable
Where the whole of the required cable can be taken off the drum in the initial pull but only
part of this is laid directly in the trench, the surplus can be coiled to a suitable position in the
manner shown in the below. The cable should be subsequently rolled out by a similar
method. The coil diameter should not fall below the minimum-bending radius of the cable.
2.3.2 Flaking Cable
Where all the required cable cannot be taken from the drum during the initial pull (i.e. if the
drum has to be mounted part way along the cable route) the cable can then be laid in the
trench up to the drum position and the remainder then flaked off the drum and laid on the
ground in the form of a figure of eight as shown in the below
3. Cable End Capping
The capping of cable ends, once the cable has been laid, is very important to prevent the
ingress of moisture. With the more modern insulating materials such as PVC, XLPE etc. the
need to prevent moisture ingress is to allow the LDPu resin to seal effectively, prevent
corrosion of aluminum conductors as well as the requirement for electrical safety when
working on these cables.
There are three preferred methods of capping cables: -
1. (a) Cold shrink cap
2. (b) Heat shrink cap
3. (c) Denso seal
