The main advantages of PVC Cables can thus be summarized as under:
- The insulation resistance and breakdown strength are practically
unaffected by moisture. These cables are thus suitable for laying even
under water.
- Cables can be overloaded for short periods without any appreciable
effect on cable life.
- The cables can be laid vertically and on steep slopes as there is no
impregnating compound involved.
- The cables are flame retardant since PVC ignites with great
difficulty and is self extinguishing.
- These cables are immune to chemicals normally encountered in
practice.
- Due to their lightweight, PVC Cables are easy to install and handle.
Small bending rapider permit the termination of these cables in limited
space.
- Low tension PVC Cables do not normally require sealing ends, when
terminated indoor. The terminations can therefore be effected quickly
and economically.
- PVC Cables have tough but smooth outer covering and are thus abrasion
proof.
- PVC cables are not affected by vibration.
- PVC Cables have high short circuit capacity since they can withstand
a high transient temperature without any deformation of insulation or
displacement of conductor.
- PVC Cables have a long service life.
Conductor
The conductor shall be composed of plain copper or aluminum wires complying
with IS: 8130-1984. Mining Cables to be used in gassy mines shall be of
copper conductor only.
Insulation
The conductors are insulated with suitably compounded PVC, which is applied
to the conductor by extrusion process.
Core Identification & Colour Scheme
Cores are identified by colour scheme of PVC insulation.
The following colour scheme is adopted.
| One core |
Red, Black, Yellow or Blue |
| Two Core |
Red and Black |
| Three Core |
Red, Yellow and Blue |
| Four Core |
Red, Yellow, Blue and Black (reduced
neutral core is also Black) |
| Five core |
Red, Yellow, Blue, Black and Light
Grey |
| For cables having more than 5 cores |
Two adjacent cores (counting and
directional) in each layer are coloured Blue & Yellow respectively
and the remaining cores are Light Grey. |
Inner Sheath
For all cables having two or more cores, a common covering (inner sheath)
is provided over the laid up cores either by extrusion or by wrapping of
plastic or proofed tapes. Single core cables do not require inner sheath.
Armouring
Depending upon the application, the cables can be armoured. The armouring
can be Round Steel Wire or Steel Strips. In case of cables where diameter
over the inner sheath does not exceed 13 mm, the armour consists of
Galvanished Round Steel Wires; above this size, the armour can be
Galvanished Flat Steel Strips or Galvanished Round Steel Wires as per
customers' requirement. In case of single core cables intended for use of an
A.C. Systems, the armouring shall be of Aluminium Wires/Stripes or any other
non-magnetic material.
Armouring of PVC Mining Cables consist of Galvanised Round Steel
Wires/Strips, but wherever necessary, a few Tinned Copper Wires/Strips are
also included to meet the resistance requirements of armouring for Mining
Cables.
Outer Sheath
Over the armouring, or in case of unarmoured mechanical control cables,
over the inner sheath (for single core cables over the insulation), a tough
outer sheath of PVC is applied by extrusion. This is normally Black in
colour. This provides a tough but smooth outer covering to PVC Cables. The
trademark "HMT" along with the year/code of manufactured are
embossed on the outer sheath. Wherever desired the customer name can also be
embossed on the cable. The embossing script repeats at desired length of
electrical control cables
Type Designation
The following code is used for designating the type of cable.
| Constituents |
Code |
| Aluminium conductor |
A |
| PVC insulation |
Y |
| Steel round wire armour |
W |
| Steel strip armour |
F |
| Steel double round wire armour |
WW |
| Steel double strip armour |
FF |
| PVC outer sheath |
Y |
Testing of PVC Cables
Testing is a vital part of cable manufacturing and all raw materials and
finished cables are thoroughly tested to ensure quality control. HMT has a
well equipped testing laboratory for carrying out electrical, mechanical and
chemical tests which are required as per relevant specifications. The
various tests as provided in the Indian Standards are carried out on HMT
Cables. These are classified in three different groups:
- Routine Tests
- Type Tests
- Acceptance Test
Routine Tests
The following tests constitute Routine Tests, which are carried out on each
and every length of cable before it leaves the factory :
Conductor Resistance Test
This test ensures that conductor resistance is with the specified limits,
thereby ensuring that the continuity of conductor is maintained throughout
the cable length and that the conductor has the required cross section area.
The DC resistance is measured at room temprature and is then corrected to
standard reference temperature at 20°C.
High Voltage Tests
This test ensures that the insulation will safely withstand the rated
voltage within permissible normal operation.
Type Tests
These tests are carried out on samples taken from each production lot. They
are carried out to prove conformity as regards the general qualities and
design to the specification of particular type of cable. These tests are
enumerated in the relevant Indian Standards.
Acceptance Tests
The customers can request the various acceptance tests as provided in the
relevant Indian Standard to be carried out before accepting the cables.
