CABLING INSTALLATION
a) The cables shall be laid in RCC cable trenches / GI pipes / cable trays /
directly buried in the ground. In paved area cable shall be laid in GI
pipes only.
b) Except civil work of RCC cable trenches, Excavation of trenches of
required width and depth in all types of soil Clearing natural
obstructions including rock cutting if any required along the cable
routing , Laying of cable on 8 cm of riddled sand and covered with 8
cm of riddled sand providing 75mm thick RCC cover slabs back filling
with earth (after cable laying), and finally compacting to original ground
level of cable trenches, all other equipment, materials and
components required for cable laying is included in the scope of work.
c) The maximum trench depth shall normally be 1.5m If the trench is to
cross railway tracks / roads or any load bearing area the cables shall
be taken through suitable GI conduits/ pipes / ducts. Installation of
cables directly buried in ground shall generally conform to the
requirements given in IS: 255.
d) Cables laid directly in underground trenches (where permitted by
owner/consultant) shall be in one layer only, more than one layer is not
permissible.
e) For crossing the road / rail track, cables shall be laid in concrete cable
ducts/ Hume pipes/ GI pipes. 25% spare duct /pipe openings / pipes
shall be available.
f) The scope includes but not limited to,
i) Cable inspection and handling.
ii) Laying, meggering, termination, dressing and clamping of cables.
iii) Tagging and marking of cables.
iv) HT/LT tests on cable.
v) Identification of phases.
vi) Connection of equipment.
vii) Making of cabling ready for charging after completing all
associated works.
IMPORTANT NOTE
a) For cable installation / laying, if cutting of foundations or structures is
required, prior permission shall be obtained from the owner/ engineer.
b) Wherever a cable crosses a temperature expansion joint in structure,
sufficient sag shall be provided.
c) Cable trays / racks shall not be used as a walkway or ladder either
during installation or while cable pulling or at any other time of
installation.
d) Cables of different voltage levels and noise classification if any,
shall be taken on different trays/racks (or other means specified).
When cables of different voltage levels or noise classes are installed
on the same tray/ rack/place, the same shall be separated by
grounded steel barrier. In no case instrument cables are to be run
along with power cables.
CABLE INSPECTION AND HANDLING
a) On receipt of cable drums at site, the contractor shall inspect each
cable drum and check for size, length and type with respect to
supplier’s seal and marking / documents.
b) Loading and unloading of cable drums shall be done by crane and
drums shall be carefully lifted and deposited on ground. If crane is not
available then the drum shall be carefully rolled down on a suitable
ramp of rails. The drum shall be rolled as per the direction indicated
by the arrow on the drum in order to prevent the turns of the cable
from loosening on the drum. Under no circumstances shall a drum be
dropped to the ground as the shock may cause serious damage to the
inner layer of cables.
c) No cable drum shall be slung, except, by a bar or spindle through the
center of the drum.
d) In no case, the drum is stored on the flat i.e. with the flanges horizontal.
e) Only cable jacks shall be employed for removing the cable from the
drum. For removing the cables from the drums, the drum should be
properly mounted on jacks on a cable wheel, making sure that the
spindle is strong enough to carry the weight without bending and that
it is laying horizontally in the bearings so as to prevent the drum
creeping to the one side or the other while it is rotating. The drums
should be mounted such that when the drum is turned against the
direction of arrow, the cable is payed out from the top of the drum to
avoid any danger of bending and breaking the cable if unreeled
from the bottom.
CABLE PULLING AND LAYING
a) Cable rollers shall be used for pulling and laying of cables. Cable shall
be properly handled while laying to avoid damage to the cables.
b) Cables may be pulled by hand or by the use of pulling eye securely
clamped to the conductors. Jacket armour or outer jacket shall be
secured to the clamp to prevent relative movement. If mechanical
means are used to pull on the conductors, force must not exceed
values recommended by the manufacturer.
c) When pulling cables, the bending radius, pulling tensions and wall
pressure at bends shall be strictly in accordance with cable
manufacturer's recommendations.
d) The pulling eye shall be securely fastened to the ends of all the
conductors so that the load is evenly distributed. The ends of all
cables to which pulling eyes are attached shall be cut off before
terminations are made. Bending radius for permanent bends shall not
be less than 15 (fifteen) times outer diameter of the cable.
CABLE CUTTING AND SPLICING
a) Cables cut from the drums, and distributed for various route lengths
shall be carefully planned bearing in mind that splices shall not be
allowed except on specified approval for larger length (cable
splices are not permitted normally).
b) All cables shall be cut to required lengths only after assessment of
correct lengths required, by actual measurement at site. The
contractor shall ensure that wastage of cables as short lengths is
minimized, by resorting to most economical cable cutting schedule.
CABLING ON TRAYS/RACKS
Cabling may have to be carried out
a) on ladder type (GI / FRP) cable trays/slotted channels.
b) In rigid steel conduits.
c) In perforated type GI / FRP trays.
d) in duct banks or embedded conduits, and
e) Buried underground/in concrete cable trenches.
¾ Lighting, Power and control cables shall be properly segregated and
clamped on the trays/racks.
¾ A clearance equal to one diameter of the bigger cables shall be
maintained between two adjacent higher rated power cables on the
trays/racks/ risers and clamped by separate clamps which shall follow
the profile of the cable. Common clamping/ strapping shall be done for
a bunch of control cables and small power cables.
¾ Cables shall be clamped at every 1.5 meters on the trays/racks slotted
channels in trenches.
¾ Cable leading to cable box of equipment shall be supported at a
distance of 450 mm from cable gland/cable box and cable gland shall be
suitably earthed.
¾ Cable shall be clamped only after the cables are neatly arranged,
dressed and kept in position.
CABLING IN CONDUITS/PIPES
a) Cables through floor slabs/walls are to be passed through rigid,
galvanized steel conduit.
b) Cables entering or leaving the conduits shall be sealed with non-
hardening silicon compounds. It is also contractor's responsibility to
satisfy him-self regarding the conditions of the embedded conduits.
Prior to pulling cables, each duct shall be rodded by suitable means.
After rodding a 8 gauge pulling wire is to be left in each duct. The ends
of the conduits shall be plugged when work is halted for any period of
time.
c) Laying of cables(in trenches in ground subject to owner’s Consultant’s
permission)
d) Cables shall be laid direct in ground in all kinds of soil or in the
prepared RCC ducts. If required, 100 mm dia (min.) GI pipe shall be
provided wherever these cables cross the roads/water lines, sewerage
lines etc. GI pipe shall also be provided wherever the cables enter the
building.
e) Cables terminating to any equipment shall also be encased in a GI pipe
raising from the ground level to the equipment connection.
f) Cable racks for cable trays shall be fixed at a maximum interval of
1.5m
g) Cables leaving the ground / floor shall be protected up o 2m height by
conduits / metallic guards.
h) Ladder type cable racks and trays shall be provided to lay cables.
Cables shall be laid in separate racks according to the voltage /
application classification.
i) All necessary frame works and fixings for the support of cables And
accessories shall be supplied.
j) Cables shall be suitably protected against heat & Mechanical
damages.
Size of cable GI pipe
Up o 4 x 50 sq.mm : 65 mm dia
3 ½ x 70 - 3 ½ x 90 Sqmm : 80 mm dia
3 ½ x 120 - 3 ½ x 185 sq.mm : 100 mm dia
3 ½ x 240 to 400 sq.mm : 125 mm
k) Approximately 3 m of surplus cable shall be left on each end of the
cable, on each side of the underground joint, at entries and places as
may be decided by the engineer-in-charge. The surplus cable shall be
left in the form of a loop.
l) The trench cut through the road-ways or other paved areas inside
building shall be restored to the same density and materials as in the
surrounding areas at no extra cost. Black-toping of the road will,
however, is not done by the contractor.
m) Cable route markers shall be provided along straight runs of the
cable and at locations approved by the engineer-in-charge, at
intervals generally not exceeding 30 meters.
n) Wherever cables are taken in conduits both ends of the conduits shall
be sealed after laying the cable to avoid the ingress of water.
o) All associated materials like sand, bricks, clamps and route markers
etc., shall be supplied by the contractor. The cost for laying of cables
shall be inclusive of all these items.
p) Laying of cables on walls/columns/ceiling/structures
q) All the lighting cables are to be neatly bunched and laid on surface of
walls/ columns/ ceiling / structures. All the cables laid on surface of
walls / columns / ceiling shall be supported by using clamps / rawl
plugs and screws / cable hooks. No wooden plugs shall be used.
r) All the cables laid on structures shall be fixed with suitable clamps.
s) Care is to be taken while laying/pulling so that insulation of cables
does not get damaged.
t) Cables are to be supported at minimum regular intervals of 0.5 m
horizontal and 1 m vertical run.
CABLE ENTRY AT BUILDINGS
a) Pressure seals and fire barriers shall be provided at the places where
cables enter pressurized electrical rooms.
b) All wall openings shall be effectively sealed after installation of cables
to avoid water leakage.
c) Wherever buried cables enter the buildings the same shall be taken
through GI pipes embedded at the entry portion. After taking cables
through the above pipes, the same shall be sealed by using suitable
compound so as to avoid ingress of water.
