Electric wires and cables have become such an important part of everyday life that without
them the world as we know it would simply not exist. For without wires and cables the existence
and operation of conveniences such as electric lights, telephones, computers and a host of other
household appliances would not have been possible. Moreover, as the standard of living rises, so
does the demand for those types of products. Consequently, there has been an incredible increase
in the demand for electric wire and cable. As developing nations around the world continue to
For example, Taiwan, the Republic of China, a country with a population of only 19 million,
has more than one hundred factories successfully producing electric wire and cable to satisfy the
needs of the domestic market. According to an estimate made in 1984,the total production of
electric wire and cable had reached a level of 200,000 tons per year. Furthermore, the vast
majority of this cable was purchased domestically by retailers, manufacturers, construction
contractors, and the government owned power and telephone companies. Clearly, the
establishment of an electric wire and cable making plant is a project worthy of investment.
The wire and cable making plant described in this particular proposal is designed for the
production of wire and low voltage (below 600V) power cable. It is not intended to be used for
the production of telecommunication or high voltage power cable, as the plants capable of
producing these types of cable are considerably more expensive and require a higher level of
technical knowledge to set up. The types of wire and cable which can be produced by the
Multiple wires: PVC insulated copper conductors consisting of 7-61 stranded wires.
Flexible wire: single or twin core, PVC insulated cords consisting of 20-100 fine copper
Flat twin-cord wire: twin core, PVC insulated single or multiple copper conductors,
Power cables: three of four cores of PVC insulated multiple copper conductors assembled
Armour cable: power cables consisting of three or four round and shaped cores armored
with steel wires and sheathed with PVC layers.
2. General Process Information
Bulk copper is formed into wire of varying diameters by drawing it through a series of dies.
Since the drawing process causes the copper to become hard and brittle, it should be annealed.
Anywhere from 20-100 (very fine copper conductor wires) are twisted into cords which will be
used in making flexible wire and cable.
Layers of wires (1+6+12+18+24 etc.) are stranded together to make copper conductors. The
maximum nominal cross-section area of a power cable core is 500m㎡.
The copper conductors, whether they are single wire or multiple stranded wire, are covered by
PVC for current insulation.
Three or four of these PVC insulated copper conductors are assembled into power cables.
Complete cables are formed by sheathing twin-core or multiple-core PVC insulated copper
conductors with PVC.
Special purpose power cables must be surrounded with steel wires in order to increase the cable
*For Special Purpose Power Cable Only.
2.2. Flow Chart
3. Plant Description
According to investor’s different situations, we classify the plant within three sizes.
Copper consumption Production capacity
Medium plant 120 Tons/month
- - 8.0mm or 2.6mm diameter copper rod (70% of the product weight)
In order to save money for the beginning investors, it is more economical to purchase 8mm (or
2.6mm) diameter copper rod and PVC grains as raw materials. These raw materials can be
supplied by Taiwan. For the detail information, please contact the supplier in Taiwan.
Mini plant Small plant Medium plant
Skilled operator 8
Name of Machinery
Mini Small Medium
8mmØ copper rod breakdown machine
Medium Wire drawing machine
Fine Wire drawing machine
(7) Drawing dies polishing machine
(1) Requirement of water (KL/month)
Mini plant Small plant Medium plant
(2) Power requirement capacity (KW)
Mini plant Small plant Medium plant
(4) Lower humidity and far from the seashore
3.8. Area of land and plant building (square meter)
Mini plant Small plant Medium plant
Plant building 1,500
17. 90mm PVC insulation and sheathing machine
21. Maintenance room
In order to transmit high voltage power, there is a need to use a cable that has the necessary
qualities for the transmission of large quantities of electricity. Overhead power line entails
transmission of electricity using towers. Moreover, another way to transmit electricity is through
utility poles. Overhead transmission method tends to be the most commonly used way of
transmitting high voltage power because most of the insulation is provided by air. This method is
less costly especially when transmitting large quantities of electricity. In order to accomplish this
obligation, the most efficient cable to use is aluminum. This paper explores aluminum as the best
cable to use in high voltage transmission lines and the process used in making the cable.
Properties of Aluminum
Physical and chemical properties of aluminum
Some of the physical properties include that aluminum is a slivery white metal. The metal is also
reflective to heat. Moreover, aluminum metal can be produced to various different forms with the
help of machines. This means that the metal can have various surface finishes. Another physical
property of aluminum is that it is easily recyclable. One of the chemical properties of aluminum
is that it is resistance to oxidation. The other chemical property is that the metal is created using
an electronic method.
Good conductor of electricity
Aluminum cable tends to be the best to use in high voltage transmission lines compared to cables
made from other metals. One of the advantages of using aluminum cable is that it is a good
conductor of electricity (Warne, 2005). This means that the metal has a low electrical resistivity.
The reason why aluminum is a good conductor of electricity is that it has 3+ charges. This means
that aluminum has three delocalized electrons that tend to move freely in each atom of the metal.
The relationship between of electricity and aluminum is that when there is an electrical field
applied on the metal, every loose electron is able to move freely. This translates that all the loose
electrons will move towards the positive terminal where there is presence of an electric field.
Eventually aluminum ends up being a good conduct of electricity hence eligible to use in
transmission lines (Warne, 2005). The metal is also a very good thermal conductor.
Light in weight
The other significant importance that makes aluminum to be the best cable while using in high
voltage transmission lines is its lightweight. Comparing aluminum with other metals like copper,
nickel and brass, aluminum tends to be less in weight to about one third of the others. The other
aspect in relation to weight is that aluminum has a specific gravity of 2.7. This means that the
metal is very light in weight. Moreover, aluminum cables being of lightweight makes them most
efficient for overhead transmission of electricity. Another significant importance of aluminum
being lighter is that cables made from the metal require little support.
Another significant feature about aluminum is that it is economical. Aluminum cables poses as
the most economical compared to other cables form other metals. Moreover, the production of
aluminum is also economical. Most of the production sites of aluminum tend to be near the
sources areas and therefore costs related to transportation are less. Another significant issue
related to less cost in aluminum is that the metal is recyclable. Moreover, aluminum being of low
cost enables cables made from this metal to move for a longer distance (Vargel, 2004).
The other reason behind choosing aluminum as the best cable is that it is resistant to corrosion.
Aluminum is able to resist corrosion because of presence of a thin layer on its surface. The thin
layer lining is made of aluminum oxide. Moreover, using technology, this particular layer can be
made stronger by anodizing the metal. Anodizing refers converting the metal to anode. This is
done in electrolysis of dilute sulphuric acid. However, in order to accomplish this step, there is a
need to first etch the aluminum with sodium hydroxide solution. This is done in order to remove
the existing oxide layer. After electrolyzing the aluminum article, a thick film of oxide is build
up that is highly resistance to corrosion.
Ductility and Malleability
The other feature associated with aluminum is that it is highly ductile. Apart from being highly
ductile, aluminum has a high aspect of malleability. Both ductility and malleability are properties
related to how the possibility of deformation can occur on a particular metal. Aluminum holds
both of these properties and therefore seems to be the best while using as electrical cables. In all
metals, aluminum is the second malleable one. While in the aspect of being ductile, aluminum
holds the sixth position in all metals. Both of the two properties are of significant importance
when using in electrical cables. This is because; malleability refers to the ability of a metal to be
deformed by compression. Moreover, this process ought to occur without cracking without or
rupturing. This feature also translates that it is possible to roll aluminum into several sheets.
Aluminum holds a high percentage on this specific feature. Ductile means that aluminum has the
ability to be deformed plastically. This process ought to occur without fracture under tensile
force. This feature also illustrates that aluminum can be easily drawn into wires. Aluminum also
tends to have high percentage on this feature. Both of these properties make aluminum to be the
perfect metal for drawing large cables that are recommendable for overhead lines.
Aluminum has another significant property of being highly strength (Fraden, 2010). This makes
aluminum cables to be the best in making overhead lines because the high strength helps the
cables not to creep. Aluminum metal is also non-magnetic. This property makes aluminum to be
the best in making cables because they cannot attach to each other in case they are swung by
Characteristics of Aluminum cables
One of the characteristics of aluminum cables is that they tend to lose some of their strength
during the high temperatures. However, even in during these periods, ductility of the metal
remains the same as in low temperatures. This feature makes aluminum to the best in cabling
even in cold regions. The other characteristic of aluminum cables is that they are able to form a
layer of oxide. The importance of these layers is that they are corrosion resistant. When
repeatedly used, the cables made from aluminum tend to lose their strength. Therefore, they
require extra care when handling.
Process and Manufacturing the Power Transmission Lines Using Aluminum Cables
High voltage electric transmission entails transfer of energy form an electric source to various
substations. Most of the substations are located near residential places. This network of
transferring electricity from the source to the final consumer is generally known as distribution
system. The importance of using overhead line transmission is because the method is less costly.
Most of the aluminum conductors were being manufactured from pure aluminum (ECAL) in the
early period. In order to make the overhead transmission lines, most of the manufactures used
wire rods. The wire rods were made through the process of hot rolling. The wire rods were also
made through extrusion methods. However, nowadays, in order to process and manufacture
transmission lines using aluminum cables, a set systematic system is used to make sure that the
best product is made.
Material and properties
The most important materials include the recommended composite conductor. The conductor
ought to have a number of zirconium strands that are made from aluminum. These specific
strands ought to be of high temperatures. Another significant property required is reinforced
composite wires that have to be of aluminum oxide. The reinforced wires are covered by the
zirconium strands. The significant importance of both the composite wires that make the
composite core and outer core aluminum-zirconium (Al-Zr) is that they help in making the
transmission lines to have the overall conductor strength and conductivity.
The composite core or the inner strands are made of aluminum composite wires. Most of the
wires depend on the conductor size and the wire diameters. In most of the time, the wire
diameters range from 0.073‖ (1.9mm) to 0.114 (209mm). One significant feature of the core
wires is that they have the stiffness and strength of steel. However, the core wires have little
weight and higher conductivity compared to materials made from steel. This is an advantage to
of the aluminum materials in making strong and reliable transmission wires. Each of the core
wire is composed of a large numbers of aluminum oxide fibers. The fibers are small in diameters
and they are of ultra-high strength. The other aspect of the composite core is that the ceramic
fibers are continuous. They are oriented in the direction of the wire. The ceramic wires are also
embedded with high-purity aluminum. The composite wires are different from aluminum itself in
strength. Moreover, the wires tend to exhibit various mechanical and physical properties that are
of more degree compared to that aluminum.
The outer strands compromise of a temperature resistance alloy. The specific alloy is aluminumzirconium. This particular alloy is of made of hard aluminum. The other significant feature is
that this particular alloy is designed to maintain high strength. This in many cases occurs after
high temperatures. The following figure shows how the outer strands of the transmission wire
ought to be.
After finding the necessary and recommended materials, the other process is making laboratory
tensile tests. The test strength is made in a gauge facility that is 10ft in length. During this
process, there is a need to take considerable care when handling the materials. Moreover, there is
also significant advantage in cutting and preparing the materials in order to ensure that the wires
did not slacken. Disadvantage of slacken is that the wires might decrease their strength values.
The other issue that is determined while checking the tensile strength is the breaking load. This is
usually done by pulling a conductor to a 1000-lb load. Then the load is further loaded to failure
at 10000 lbs/min. After the testing the tensile strength, the breaking load ought to reach the
recommended Rated Breaking Strength (RBS).
Stress strain behavior
Another significant issue addressed during the manufacturing process of the transmission lines is
the stress-strain behavior. The behavior is determined according to the set standards by the
Aluminum Association. The stress-strain behavior is test is started at 1000lbs (4.4KN). During
this process, the strain measurement is set at zero. The load is then incrementally increased to a
percentage of between 30 and 75 of RBS. Moreover, curve fitting is then applied to the
transmission lines (Kaufman, Rooy & American Foundry Society, 2004).
Short Circuit Behavior
This test is conducted in order to determine whether the aluminum cable is able to sustain the
compression that might occur in case of short circuits. The following figure demonstrates the
consequences that might occur during a short circuit while using cables other than aluminum.
Axial Impact strength
This is a test usually done to investigate whether there is slippage in conductor terminations. The
other significant importance of this test is to investigate whether there is a possibility to sustain
the high shock loads (>100% RBS). In most cases, the loads ought to be sustained by the 795-
kcmil Composite Conductor. Moreover, this is done under high rate axial loading. Through this
particular process, the shock load is comparable to various loading rates. Some the loading rates
include those experienced in certain situations like during ice jumps and galloping events. The
following figure demonstrates an axial impact.
The crush strength test is usually done to test the full strength retention of the aluminum cable.
The test is done on a 795-kcmil Composite Conductor. The main reason for conducting the test is
to simulate the possible damage that might occur during the process of shipping and installation.
An example of this process is crushing a section of the aluminum cable between 6-inch steel
plates for a period of one minute. If the aluminum cable shows any detection of damage, then the
cable it is not fit for application.
This is a significant process usually undertaken during the process of manufacturing overhead
transmission lines. A lightening arc is struck across the aluminum cable to determine whether it
can be able to resist very severe strikes (Smith, 2008). The following figures demonstrate two
types of cables where one is able to resist occurrence of lightening while the other one is not.
After the aluminum cable, is able to pass through all the above manufacturing processes, then it
eligible for application in overhead transmission lines. Aluminum tends to be the best metal for
making transmission cables as illustrated above. Transmission of high-voltage electricity
requires cables that are able to resist various manufacture and environmental unhealthy
conditions. Through various developments in technology, it is possible to make aluminum cables
in an easy way compared to the methods that were used in the past. Moreover, through
technology there is a possibility of extra advancement in making the overhead aluminum cable
lines. Aluminum cables poses to be the best compared with other metals.
2 Cable Parts
2.2 Conductor Screen
2.4 Insulation Screen
2.5 Conductor Sheath
2.7 Bedding / Inner Sheath
2.8 Individual Screen (Instrument Cables)
2.9 Drain Wire (Instrument Cables)
2.10 Overall Screen (Instrument Cables)
2.12 Outer Sheath
2.13 Termite Protection
2.14 Conductor Protection (Appendix)
3 Low Voltage Power and Control Cables
4 Low Voltage Instrumentation Cables
5 Medium / High Voltage Power Cables
5.1 Teck Cables
5.2 Shielded Cables
5.3 Concentric Neutral Cables
5.4 Paper-Insulated Lead-Covered Cables (PILC)
5.5 Submarine Cables
5.6 Mining Cables
5.7 Aluminum-Sheathed Cables
This article gives a brief exposition on the construction of typical low voltage, medium / high
voltage and instrumentation cables. The focus is on thermoplastic and thermosetting insulated
cables, however the construction of other cables are similar. Although there is more than one
way to construct a cable and no one standard to which all vendors will adhere, most cables tend
to have common characteristics.
Low voltage power and control cables pertain to electrical cables that typically have a
voltage grade of 0.6/1 kV or below.
Low voltage instrumentation cables pertain to cables for use in instrument applications
and typically have a voltage grade of 450/750 V or below.
Medium / High voltage cables pertain to cables used for electric power transmission at
madium and high voltage (usually from 1 to 33 kV are medium voltage cables and those
over 50 kV are high voltage cables).
Here, we will take a short overview of the main and the most typical cable construction parts:
Usually stranded copper (Cu) or aluminium (Al). Copper is densier and heavier, but more
conductive than aluminium. Electrically equivalent aluminium conductors have a cross-sectional
area approximately 1.6 times larger than copper, but are half the weight (which may save on
Annealing – is the process of gradually heating and cooling the conductor material to make it
more malleable and less brittle.
Coating – surface coating (eg. tin, nickel, silver, lead alloy) of copper conductors is common to
prevent the insulation from attacking or adhering to the copper conductor and prevents
deterioration of copper at high temperatures. Tin coatings were used in the past to protect against
corrosion from rubber insulation, which contained traces of the sulfur used in the vulcanising
A semi-conducting tape to maintain a uniform electric field and minimise electrostatic stresses
(for MV/HV power cables).
Commonly thermoplastic (eg. PVC) or thermosetting (eg. EPR, XLPE) type materials. Mineral
insulation is sometimes used, but the construction of MI cables are entirely different to normal
plastic / rubber insulated cables. Typically a thermosetting(eg. EPR, XLPE) or paper/lead
insulation for cables under 22kV. Paper-based insulation in combination with oil or gas-filled
cables are generally used for higher voltages.
Plastics are one of the more commonly used types of insulating materials for electrical
conductors. It has good insulating, flexibility, and moisture-resistant qualities. Although there are
many types of plastic insulating materials, thermoplastic is one of the most common. With the
use of thermoplastic, the conductor temperature can be higher than with some other types of
insulating materials without damage to the insulating quality of the material. Plastic insulation is
normally used for low- or medium-range voltage.
The designators used with thermoplastics are much like those used with rubber insulators. The
following letters are used when dealing with NEC type designators for thermoplastics:
T - Thermoplastic
H - Heat-resistant
W - Moisture-resistant
A - Asbestos
N - Outer nylon jacket
M - Oil-resistant
Paper has little insulation value alone. However, when impregnated with a high grade of mineral
oil, it serves as a satisfactory insulation for extremely high-voltage cables. The oil has a high
dielectric strength, and tends to prevent breakdown of the paper insulation. The paper must be
thoroughly saturated with the oil. The thin paper tape is wrapped in many layers around the
conductors, and then soaked with oil.
Enamel: the wire used on the coils of meters, relays, small transformers, motor windings, and so
forth, is called magnet wire. This wire is insulated with an enamel coating. The enamel is a
synthetic compound of cellulose acetate (wood pulp and magnesium). In the manufacturing
process, the bare wire is passed through a solution of hot enamel and then cooled. This process is
repeated until the wire acquires from 6 to 10 coatings. Thickness for thickness, enamel has
higher dielectric strength than rubber. It is not practical for large wires because of the expense
and because the insulation is readily fractured when large wires are bent.
Mineral-insulated (MI) cable was developed to meet the needs of a noncombustible, high heatresistant, and water-resistant cable. MI cable has from one to seven electrical conductors. These
conductors are insulated in a highly compressed mineral, normally magnesium oxide, and sealed
in a liquidtight, gastight metallic tube, normally made of seamless copper.
Silk and Cotton: in certain types of circuits (for example, communications circuits), a large
number of conductors are needed, perhaps as many as several hundred. Because the insulation in
this type of cable is not subjected to high voltage, the use of thin layers of silk and cotton is
Silk and cotton insulation keeps the size of the cable small enough to be handled easily. The silk
and cotton threads are wrapped around the individual conductors in reverse directions. The
covering is then impregnated with a special wax compound.
A semi-conducting material that has a similar function as the conductor screen (ie. control of the
electric field for MV/HV power cables).
A conductive sheath / shield, typically of copper tape or sometimes lead alloy, is used as a shield
to keep electromagnetic radiation in, and also provide a path for fault and leakage currents
(sheaths are earthed at one cable end). Lead sheaths are heavier and potentially more difficult to
terminate than copper tape, but generally provide better earth fault capacity.
The interstices of the insulated conductor bundle is sometimes filled, usually with a soft polymer
Bedding / Inner Sheath
Typically a thermoplastic (eg. PVC) or thermosetting (eg. CSP) compound, the inner sheath is
there to keep the bundle together and to provide a bedding for the cable armour.
Individual Screen (Instrument Cables)
An individual screen is occasionally applied over each insulated conductor bundle for shielding
against noise / radiation and interference from other conductor bundles. Screens are usually a
metallic (copper, aluminium) or semi-metallic (PETP/Al) tape or braid. Typically used in
instrument cables, but not in power cables.
Drain Wire (Instrument Cables)
Each screen has an associated drain wire, which assists in the termination of the screen.
Typically used in instrument cables, but not in power cables.
Overall Screen (Instrument Cables)
An overall screen is applied over all the insulated conductor bundles for shielding against noise /
radiation, interference from other cables and surge / lightning protection. Screens are usually a
metallic (copper, aluminium) or semi-metallic (PETP/Al) tape or braid. Typically used in
instrument cables, but not in power cables.
For mechanical protection of the conductor bundle. Steel wire armour or braid is typically used.
Tinning or galvanising is used for rust prevention. Phosphor bronze or tinned copper braid is also
used when steel armour is not allowed.
SWA - Steel wire armour, used in multi-core cables (magnetic),
AWA - Aluminium wire armour, used in single-core cables (non-magnetic).
When an electric current passes through a cable it produces a magnetic field (the higher the
voltage the bigger the field). The magnetic field will induce an electric current in steel armour
(eddy currents), which can cause overheating in AC systems. The non-magnetic aluminium
armour prevents this from happening.
Applied over the armour for overall mechanical, weather, chemical and electrical protection.
Typically a thermoplastic (eg. PVC) or thermosetting(eg. CSP) compound, and often the same
material as the bedding. Outer sheath is normally colour coded to differentiate between LV, HV
and instrumentation cables. Manufacturer’s markings and length markings are also printed on the
For underground cables, a nylon jacket can be applied for termite protection, although sometimes
a phosphor bronze tape is used.
Conductor Protection (Appendix)
Wires and cables are generally subject to abuse. The type and amount of abuse depends on how
and where they are installed and the manner in which they are used. Cables buried directly in the
ground must resist moisture, chemical action, and abrasion. Wires installed in buildings must be
protected against mechanical injury and overloading. Wires strung on crossarms on poles must
be kept far enough apart so that the wires do not touch. Snow, ice, and strong winds make it
necessary to use conductors having high tensile strength and substantial frame structures.
Generally, except for overhead transmission lines, wires or cables are protected by some form of
covering. The covering may be some type of insulator like rubber or plastic. Over this, additional
layers of fibrous braid or tape may be used and then covered with a finish or saturated with a
protective coating. If the wire or cable is installed where it is likely to receive rough treatment, a
metallic coat should be added.
The materials used to make up the conductor protection for a wire or cable are grouped into one
of two categories: non-metallic or metallic.
The category of non-metallic protective coverings is divided into three areas. These areas are:
(1) according to the material used as the covering,
(2) according to the saturant in which the covering was impregnated, and
(3) according to the external finish on the wire or cable.
These three areas reflect three different methods of protecting the wire or cable. These methods
allow some wire or cable to be classified under more than one category. Most of the time,
however, the wire or cable will be classified based upon the material used as the covering
regardless of whether or not a saturant or finish is applied.
Many types of non-metallic materials are used to protect wires and cables. Fibrous braid is by far
the most common and will be discussed first.
Fibrous braid is used extensively as a protective covering for cables. This braid is woven over
the insulation to form a continuous covering without joints. The braid is generally saturated with
asphalt, paint, or varnish to give added protection against moisture, flame, weathering, oil, or
acid. Additionally, the outside braid is often given a finish of stearin pitch and mica flakes, paint,
wax, lacquer, or varnish depending on the environment where the cable is to be used.
Woven covers, commonly called loom, are used when exceptional abrasion-resistant qualities are
required. These covers are composed of thick, heavy, long-fibered cotton yarns woven around
the cable in a circular loom, much like that used on a fire hose. They are not braids, although
braid covering are also woven; they are designated differently.
Rubber and Synthetic Coverings
Rubber and synthetic coverings are not standardized. Different manufactures have their own
special compounds designated by individual trade names. These compounds are different from
the rubber compounds used to insulate cable. These compounds have been perfected not for
insulation qualities but for resistance to abrasion, moisture, oil, gasoline, acids, earth solutions,
and alkalies. None of these coverings will provide protection against all types of exposure. Each
covering has its own particular limitations and qualifications.
Jute and Asphalt Coverings
Jute and asphalt coverings are commonly used as a cushion between cable insulation and
metallic armour. Frequently, they are also used as a corrosive-resistant covering over a lead
sheath or metallic armour. Jute and asphalt coverings consist of asphalt-impregnated jute yarn
heli-wrapped around the cable or of alternate layers of asphalt-impregnated jute yarn. These
coverings serve as a weatherproofing.
Unspun Felted Cotton
Unspun felted cotton is commonly used only in special classes of service. It is made as a solid
felted covering for a cable.
Metallic protection is of two types: sheath or armour. As with all wires and cables, the type of
protection needed will depend on the environment where the wire or cable will be used.
Cables or wires that are continually subjected to water must be protected by a watertight cover.
This watertight cover is either a continuous metal jacket or a rubber sheath molded around the
Lead-sheathed cable is one of three types currently being used: alloy lead, pure lead, and
reinforced lead. An alloy-lead sheath is much like a pure lead sheath but is manufactured with 2percent tin. This alloy is more resistant to gouging and abrasion during and after installation.
Reinforced lead sheath is used mainly for oil-filled cables where high internal pressures can be
expected. Reinforced lead sheath consists of a double lead sheath. A thin tape of hard-drawn
copper, bronze, or other elastic metal (preferably nonmagnetic) is wrapped around the inner
sheath. This tape gives considerable additional strength and elasticity to the sheath, but must be
protected from corrosion. For this reason, a second lead sheath is applied over the tape.
Metallic armour provides a tough protective covering for wires and cables. The type, thickness,
and kind of metal used to make the armour depend on three factors:
(1) the use of the conductors,
(2) the environment where the conductors are to be used, and
(3) the amount of rough treatment that is expected.
1. Wire-braid armour
Wire-braid armour, also known as basket-weave armour, is used when light and flexible
protection is needed. Wire braid is constructed much like fibrous braid. The metal is woven
directly over the cable as the outer covering. The metal used in this braid is galvanized steel,
bronze, copper, or aluminum. Wire-braid armour is mainly for shipboard use.
2. Steel tape
A second type of metallic armour is steel tape. Steel tape covering is wrapped around the cable
and then covered with a serving of jute. There are two types of steel tape armour. The first is
called interlocking armour. Interlocking armour is applied by wrapping the tape around the cable
so that each turn is overlapped by the next and is locked in place. The second type is flat- band
armour. Flat-band armour consists of two layers of steel tape. The first layer is wrapped around
the cable but is not overlapped. The second layer is then wrapped around the cable covering the
area that was not covered by the first layer.
3. Wire armour
Wire armour is a layer of wound metal wire wrapped around the cable. Wire armour is usually
made of galvanized steel and can be used over a lead sheath (see view C of the figure above). It
can be used with the sheath as a buried cable where moisture is a concern, or without the sheath
when used in buildings.
4. Coaxial cable
Coaxial cable is defined as two concentric wires, cylindrical in shape, separated by a dielectric of
some type. One wire is the center conductor and the other is the outer conductor. These
conductors are covered by a protective jacket. The protective jacket is then covered by an outer
Coaxial cables are used as transmission lines and are constructed to provide protection against
outside signal interference.
Low Voltage Power and Control Cables
Low voltage power and control cables pertain to electrical cables that typically have a voltage
grade of 0.6/1 kV or below.
Armoured FAS Cable
An important item that is under the grouping known as 'Low Voltage Cables', is Type FAS (Fire
Alarm & Signal Cable). This 300-volt cable, is specifically designed for the interconnection of
security system elements, including fire protection signalling devices such as smoke and fire
detectors, fire alarms, and two-way emergency communications systems.
Fire alarm installations in non-combustible buildings require mechanical protection, consisting
of interlock armour, metallic conduit, non-metallic conduit embedded in concrete or installed
under-ground. Armoured FAS Cable provided with an interlocking aluminum armour, may be
expected to have an appreciable cost advantage, compared with cables installed in rigid conduit.
Other common cables are LVT (Low Voltage Thermoplastic) and ELC (Extra Low Voltage
Control), which are frequently used in residential installations for such items as door bells and
Low Voltage Instrumentation Cables
Low voltage instrumentation cables pertain to cables for use in instrument applications and
typically have a voltage grade of 450/750 V or below.
Instrumentation Cables rated at 300 volts have copper conductors 0.33 mm2 (#22 AWG) to
2.08 mm2 (#14 AWG), while those rated at 600 volts have 0.82 mm2(#18 AWG) to 5.26
mm2(#10 AWG), and unarmoured and armoured types are available. The cables may be an
assembly of single conductors, pairs, triads or quads. The conductors are stranded seven-wire
tinned or bare copper. The insulation is usually a PVC compound chosen dependant on the
environment for which it is intended. Insulated conductors are paired with staggered lays to
prevent electromagnetic coupling and crosstalk. When individual shielding is specified, each pair
is aluminum/polyester shielded with drain wire to eliminate electrostatic interference.
Armoured cables have an interlocked aluminum or galvanized steel armour. The armouring is
applied over an inner PVC jacket, followed by a PVC outer jacket. Armoured cables are suitable
for installation on cable trays in dry, damp and wet locations, or direct earth burial.
Unarmoured Instrumentation Cables are intended for installation in raceways/conduit (except
cable trays) in dry, damp or wet locations, or direct earth buried. Unarmoured Cable with Type
TC (Tray Cable) designation, may be installed in cable trays.
Thermocouple Extension Cables
Thermocouple Extension Cables have a 300 volt rating, and are of similar construction to
Instrumentation Cables, but the metals/alloys used for the conductors are different.
Thermocouples measure temperature using the electric current created when heat is applied to
two dissimilar metals/alloys. The cable assembles may consist of as many as 50 pairs, depending
on the number of locations being temperature monitored.
Medium / High Voltage Power Cables
Medium or High Voltage power cables have voltage grade greater than 1 kV. Medium voltage
usually goes up to 46 kV and High voltage is considering all voltage levels above 46 kV.
Medium Voltage distribution systems begin at substations and supply electricity to a wide
spectrum of power consumers. When selecting a cable, the basic aim is to safely provide
adequate electrical power, with continuous, trouble-free operation, in a system that is able to
withstand unexpected demands and overload conditions. Each installation has particular
requirements that must be considered. There are distinct benefits from specifying a copperconductor cable that has been manufactured under rigid specification and quality control
procedures. It will provide maximum performance with minimum maintenance. There are seven
types different by construction for medium voltage copper power cables in the 1 kV to 46 kV
range. Most are available in single- and multi-core configurations. There are ranges of sizes and
design variations for each type.
The MV cable types are:
Concentric Neutral Cables,
Paper-Insulated Lead-Covered Cables,
In the cable descriptions a number of insulation and sheath (jacket) materials have been
abbreviated as follows:
Cross-Linked Polyethylene - XLPE,
Ethylene-Propylene Rubber - EPR,
Polyvinyl Chloride - PVC,
Polyethylene - PE,
Tree-Retardant Cross-Linked Polyethylene - TR-XLPE.
Teck Cables were originally developed for use in mines, but they are now widely used in
primary and secondary industries, chemical plants, refineries and general factory environments.
They are also used in multi-storey and commercial buildings. They are flexible, resistant to
mechanical abuse, corrosion resistant, compact and reliable. A modified Teck Cable construction
may be used for vertical installations, such as in mine shafts and multi-storey buildings, where
the armour is locked-in-place to prevent slippage of the inner core. There are many different
combinations of conductor size, voltage rating, armour type and so forth, available in Teck
Cables to meet the requirements of particular installations. Annealed, bare, copper is used for the
conductor (s), and they are usually compact stranded to reduce diameter. In multi-conductor
cables, the insulated conductors are cabled together, including the bare copper bonding
(grounding) conductor. In shielded multi-conductor cables, the bonding (grounding) conductor is
positioned to contact the copper shields. A PVC outer jacket which may be colour-coded
depending on the rating of the cable is applied.
Shielded Power Cable may be single-or three-conductor. The basic construction begins with a
conductor of annealed, bare, solid or concentric-stranded copper, which may be compact or
compressed. This is followed by a semi-conducting conductor shield, insulation, and then a semiconducting insulation shield. Metallic shielding follows, which is usually either gapped or lapped
copper tape. Other types of metallic shielding are available, including concentric wires and
longitudinally corrugated copper tape. The outer jacket is either PVC or PE.
Concentric Neutral Cables
These power cables may be used in dry or wet locations, for a wide variety of types of
installations, and may be single- or three-conductor. The two standard constructions are
Unjacketed and Jacketed, the latter being most frequently used. The conductor is typically
annealed, bare, stranded copper, but tin-coated wire and solid conductors are also available. The
concentric neutral conductor, from which the cable derives its name, is bare or tin-coated copper
wire, applied helically over the insulation shield. These wires act as the metallic component of
the shield and the neutral, at the same time.
Paper-Insulated Lead-Covered Cables (PILC)
PILC cables are used in power distribution and industrial applications, and they may be installed
exposed, in underground ducts or directly buried. Their design begins with annealed, bare copper
conductor(s) which may be round, concentric, compressed or compact stranded, compact sector,
and in larger sizes … Type M segmental stranded. An example of compact sector conductors is
shown in the illustration. The insulated cable core is impregnated with a medium viscosity
polybutene-based compound. The combination of the excellent electrical and mechanical
characteristics of the liquid and the paper has resulted in a reliable and economic insulation,
which now claims a history of almost 100 years. It is little wonder why so many utilities and
power-consuming industries, still continue to specify PILC. To prevent the ingress of moisture, a
seamless lead-alloy sheath is applied. The outer jacket may be PVC or PE, and if required by the
application, armour is available.
For submarine installations, usually Self-Contained Liquid-Filled Cables (SCLF), or Solid
Dielectric Cables are selected, depending on voltage and power load. SCLF Cables are capable
of handling very high voltages. However, for medium-voltage installations, a Solid Dielectric
Cable can easily fulfil the electrical demands of the system. A submarine Solid Dielectric Cable
is shown in the illustration. Its construction begins with a compact stranded, annealed, bare
copper conductor, followed by a semi-conducting conductor shield. A copper tape shield is
helically applied, followed by a lead-alloy sheath. Due to the severe environmental demands
placed on submarine cables, a lead-alloy sheath is often specified because of its compressibility,
flexibility and resistance to moisture and corrosion. The sheath is usually covered by a number of
outer layers, comprising a PE or PVC jacket and metal wire armouring.
A number of different types of cables are used in mines. There are fixed mining cables and
portable mining cables, the latter being described here. The key requirements of portable cables
are flexibility, and resistance to mechanical abrasion and damage. Due to the additional demands
put on portable mining cables used for reeling and dereeling applications, special design may be
required. There are many types of portable mining cables. They are available in ratings up to 25
kV, and may have as many as five conductors. An example of SHD-GC Cable, is shown in the
illustration. It has three insulated, shielded conductors, two bare ground wires, a ground check
wire, and an overall jacket. The conductors for this cable are annealed, bare or tinned copper
wires. The braided shield may be tin-coated wires, or a tin-coated copper wire/textile composite.
The grounding conductor(s) annealed, bare or tinned, stranded copper wires, and the ground
check conductor is annealed, bare, stranded copper wires with EPR insulation and nylon braid,
elastomeric jacket holds the conductor assembly firmly in place, to minimize snaking and corkscrewing during reeling and dereeling.
These power cables are used for exposed and concealed wiring, in wet and dry locations, and
where exposed to the weather. They may be installed in ventilated, unventilated and ladder-type
cable-troughs, and ventilated flexible cableways. Aluminum-Sheathed Power Cables may be
single-,two-,three- or four-conductor, the conductor(s) being annealed, bare, compressed-round
stranded copper. The insulated core is enclosed in a liquid- and vapour-tight solid corrugated
aluminum sheath, covered by a PVC jacket.
A high-voltage cable - also called HV cable - is used for electric power transmission at high
voltage. High-voltage cables of differing types have a variety of applications in instruments,
ignition systems, AC and DC power transmission. In all applications, the insulation of the cable
must not deteriorate due to the high-voltage stress, ozone produced by electric discharges in air,
or tracking. The cable system must prevent contact of the high-voltage conductor with other
objects or persons, and must contain and control leakage current. Cable joints and terminals must
be designed to control the high-voltage stress to prevent breakdown of the insulation. Often a
high-voltage cable will have a metallic shield layer over the insulation, connected to earth
ground and designed to equalize the dielectric stress on the insulation layer.
Segments of high-voltage cables
High-voltage cables may be any length, with relatively short cables used in apparatus, longer
cables run within buildings or as buried cables in an industrial plant or for power distribution,
and the longest cables are often run as submarine cables under the ocean for power transmission.
2 AC power cable
o 2.1 Quality
3 HVDC cable
4 Cable terminals
5 Cable joints
6 X-ray cable
7 Testing of high-voltage cables
8 See also
9 Sources and notes
o 9.1 Notes
10 External links
A cross-section through a 400 kV cable, showing the stranded segmented copper conductor in
the center, semiconducting and insulating layers, copper shield conductors, aluminum sheath and
plastic outer jacket.
Like other power cables, high-voltage cables have the structural elements of one or more
conductors, insulation, and a protective jacket. High-voltage cables differ from lower-voltage
cables in that they have additional internal layers in the insulation jacket to control the electric
field around the conductor.
For circuits operating at or above 2,000 volts between conductors, a conductive shield may
surround each insulated conductor. This equalizes electrical stress on the cable insulation. This
technique was patented by Martin Hochstadter in 1916; the shield is sometimes called a
Hochstadter shield. The individual conductor shields of a cable are connected to earth ground at
the ends of the shield, and at splices. Stress relief cones are applied at the shield ends.
Cables for power distribution of 10 kV or higher may be insulated with oil and paper, and are run
in a rigid steel pipe, semi-rigid aluminum or lead sheath. For higher voltages the oil may be kept
under pressure to prevent formation of voids that would allow partial discharges within the cable
Sebastian Ziani de Ferranti was the first to demonstrate in 1887 that carefully dried and prepared
paper could form satisfactory cable insulation at 11,000 volts. Previously paper-insulated cable
had only been applied for low-voltage telegraph and telephone circuits. An extruded lead sheath
over the paper cable was required to ensure that the paper remained absolutely dry.
Vulcanized rubber was patented by Charles Goodyear in 1844, but it was not applied to cable
insulation until the 1880s, when it was used for lighting circuits. Rubber-insulated cable was
used for 11,000 volt circuits in 1897 installed for the Niagara Falls Power Generation project.
Mass-impregnated paper-insulated medium voltage cables were commercially practical by 1895.
During World War II several varieties of synthetic rubber and polyethylene insulation were
applied to cables. Modern high-voltage cables use polymers or polyethylene, including (XLPE)
AC power cable
High voltage is defined as any voltage over 1000 volts. Cables for 3000 and 6000 volts exist, but
the majority of cables are used from 10 kV and upward. Those of 10 to 33 kV are usually
called medium voltage cables, those over 50 kV high voltage cables.
Figure 1, cross section of a high-voltage cable, (1) conductor, (3) insulation.
Modern HV cables have a simple design consisting of few parts. A conductor of copper or
aluminum wires transports the current, see (1) in figure 1. (For a detailed discussion on copper
cables, see main article: Copper wire and cable.)
Conductor sections up to 2000 mm2 may transport currents up to 2000 amperes. The individual
strands are often preshaped to provide a smoother overall circumference. The insulation (3) may
consist of cross-linked polyethylene, also called XLPE. It is reasonably flexible and tolerates
operating temperatures up to 120 °C. EPDM is also an insulation.
At the inner (2) and outer (4) sides of this insulation, semi-conducting layers are fused to the
insulation. The function of these layers is to prevent air-filled cavities between the metal
conductors and the dielectric so that little electric discharges can arise and endanger the
The outer conductor or sheath (5) serves as an earthed layer and will conduct leakage currents if
Most high-voltage cables for power transmission that are currently sold on the market are
insulated by a sheath of cross-linked polyethylene (XLPE). Some cables may have a lead or
aluminium jacket in conjunction with XLPE insulation to allow for fiber optics. Before 1960,
underground power cables were insulated with oil and paper and ran in a rigid steel pipe, or a
semi-rigid aluminium or lead jacket or sheath. The oil was kept under pressure to prevent
formation of voids that would allow partial discharges within the cable insulation. There are still
many of these oil-and-paper insulated cables in use worldwide. Between 1960 and 1990,
polymers became more widely used at distribution voltages, mostly EPDM (ethylene propylene
diene M-class); however, their relative unreliability, particularly early XLPE, resulted in a slow
uptake at transmission voltages. While cables of 330 kV are commonly constructed using XLPE,
this has occurred only in recent decades.
During the development of HV insulation, which has taken about half a century, two
characteristics proved to be paramount. First, the introduction of the semiconducting layers.
These layers must be absolutely smooth, without even protrusions as small as a few µm. Further
the fusion between the insulation and these layers must be absolute; any fission, air-pocket or
other defect - of the same micro-dimensions as above - is detrimental for the breakdown
characteristics of the cable.
Secondly, the insulation must be free of inclusions, cavities or other defects of the same sort of
size. Any defect of these types shortens the voltage life of the cable which is supposed to be in
the order of 30 years or more.
Cooperation between cable-makers and manufacturers of materials has resulted in grades of
XLPE with tight specifications. Most producers of XLPE-compound specify an ―extra clean‖
grade where the number and size of foreign particles are guaranteed. Packing the raw material
and unloading it within a cleanroom environment in the cable-making machines is required. The
development of extruders for plastics extrusion and cross-linking has resulted in cable-making
installations for making defect-free and pure insulations. The final quality control test is an
elevated voltage 50 or 60 Hz partial discharge test with very high sensitivity (in the range of 5 to
10 picoCoulombs) This test is performed on every reel of cable before it is shipped.
An extruder machine for making insulated cable
A high-voltage cable for HVDC transmission has the same construction as the AC cable shown
in figure 1. The physics and the test-requirements are different. In this case the smoothness of
the semiconducting layers (2) and (4) is of utmost importance. Cleanliness of the insulation
Many HVDC cables are used for DC submarine connections, because at distances over 30 km
AC can no longer be used. The longest submarine cable today is the NorNed cable between
Norway and Holland that is almost 600 km long and transports 700 megawatts, a capacity equal
to a large power station.
Most of these long deep-sea cables are made in an older construction, using oil-impregnated
paper as an insulator.
Figure 2, the earth shield of a cable (0%) is cut off, the equipotential lines (from 20% to 80%)
concentrate at the edge of the earth electrode, causing danger of breakdown.
Terminals of high-voltage cables must manage the electric fields at the ends. Without such a
construction the electric field will concentrate at the end of the earth-conductor as shown in
Equipotential lines are shown here which can be compared with the contour lines on a map of a
mountainous region: the nearer these lines are to each other, the steeper the slope and the greater
the danger, in this case the danger of an electric breakdown. The equipotential lines can also be
compared with the isobars on a weather map: the denser the lines, the more wind and the greater
the danger of damage.
Figure 3, a rubber or elastomer body R is pushed over the insulation (blue) of the cable. The
equipotential lines between HV (high voltage) and earth are evenly spread out by the shape of
the earth electrode. Field concentrations are prevented in this way.
In order to control the equipotential lines (that is to control the electric field) a device is used that
is called a stress-cone, see figure 3. The crux of stress relief is to flare the shield end along a
logarithmic curve. Before 1960, the stress cones were handmade using tape—after the cable was
installed. These were protected by potheads, so named because a potting compound/ dielectric
was poured around the tape inside a metal/ porcelain body insulators. About 1960, preformed
terminations were developed consisting of a rubber or elastomer body that is stretched over the
cable end. On this rubber-like body R an shield electrode is applied that spreads the
equipotential lines to guarantee a low electric field.
The crux of this device, invented by NKF in Delft in 1964, is that the bore of the elastic body
is narrower than the diameter of the cable. In this way the (blue) interface between cable and
stress-cone is brought under mechanical pressure so that no cavities or air-pockets can be formed
between cable and cone. Electric breakdown in this region is prevented in this way.
This construction can further be surrounded by a porcelain or silicone insulator for outdoor
use, or by contraptions to enter the cable into a power transformer under oil, or switchgear
Connecting two high-voltage cables with one another poses two main problems. First, the outer
conducting layers in both cables shall be terminated without causing a field concentration,
similar as with the making of a cable terminal. Secondly, a field free space shall be created
where the cut-down cable insulation and the connector of the two conductors safely can be
accommodated. These problems have been solved by NKF in Delft in 1965  by introducing
a device called bi-manchet.
Photograph of a section of a high-voltage joint, bi-manchet, with a high-voltage cable mounted
at the right hand side of the device.
Figure 4 shows a photograph of the cross-section of such a device. At one side of this photograph
the contours of a high-voltage cable are drawn. Here red represents the conductor of that cable
and blue the insulation of the cable. The black parts in this picture are semi-conducting rubber
parts. The outer one is at earth potential and spreads the electric field in a similar way as in a
cable terminal. The inner one is at high-voltage and shields the connector of the conductors from
the electric field.
The field itself is diverted as shown in figure 5, where the equipotential lines are smoothly
directed from the inside of the cable to the outer part of the bi-manchet (and vice versa at the
other side of the device).
Field distribution in a bi-manchet or HV joint.
The crux of the matter is here, like in the cable terminal, that the inner bore of this bi-manchet is
chosen smaller than the diameter over the cable-insulation. In this way a permanent pressure
is created between the bi-manchet and the cable surface and cavities or electrical weak points are
Installing a terminal or bi-manchet is skilled work. Removing the outer semiconducting layer at
the end of the cables, placing the field-controlling bodies, connecting the conductors, etc.,
require skill, cleanness and precision.
X-ray cables  are used in lengths of several meters to connect the HV source with an X-ray
tube or any other HV device in scientific equipment. They transmit small currents, in the order of
milliamperes at DC voltages of 30 to 200 kV, or sometimes higher. The cables are flexible, with
rubber or other elastomer insulation, stranded conductors, and an outer sheath of braided copperwire. The construction has the same elements as other HV power cables.
Testing of high-voltage cables
There are different causes for faulty cable insulations. Hence, there are various test and
measurement methods to prove fully functional cables or to detect faulty ones. One needs to
distinguish between cable testing and cable diagnosis. While cable testing methods result in a
go/no go statement cable diagnosis methods allow judgement of the cables current condition. In
some cases it is even possible to locate the position of the fault in the insulation. One of the
favorite testing methods is VLF cable testing. Using a very low frequency voltage with
frequencies in the range of 0.1 to 0.01 Hz protects the device under test from deteriorating due to
the test itself, as it used to be with DC testing methods in the older days. Depending on the sort
of treeing in the insulation two cable diagnostics methods are common. Water trees can be
detected by tan delta measurement. Interpretation of measurement results yield the possibility to
distinguish between new, strongly aged and faulty cables and appropriate maintenance and repair
measures may be planned. Damages to the insulation and electrical treeing may be detected and
located by partial discharge measurement. Data collected during the measurement procedure is
compared to measurement values of the same cable gathered during the acceptance-test. This
allows simple and quick classification of the dielectric condition of the tested cable.
Cable Construction & Manufacturing
NATIONAL INSTITUTE OF INDUSTRIAL
CABLE CONSTRUCTION & MANUFACTURING
UNDER THE GUIDANCE OF
Dr. KVSS NARAYANA RAO
Cable Construction & Manufacturing Process
fig-power cable parts
Power Cable mainly subdivided into parts1. Conductor
3. Metallic Sheath
Copper or Aluminium used for the Conductors obtained in the form of rods. The 8.0 mm
Copper or 9.5mm aluminium rods. After testing, rods are drawn into wires of required sizes.
These wires are formed into final Conductor in the stranding machines under strict Quality
Cross linked polyethylene compound or PVC is insulated over Conductor by Extrusion
process. XLPE insulated cores are cured by steam curing in vulcanizing chamber to provide
The raw materials & thickness of Insulation are maintained under strict Quality Control
and conform to B.S. 5467 / IEC 60502 Part-1 or B.S. 6346 / IEC 60502 Part-1 Standards for
XLPE & PVC cables respectively.
The insulated cores are laid up with a right hand, or alternating left & right hand,
direction of lay in the sequence of the core numbers or colours. Where ever necessary nonhygroscopic PP / PVC Fillers & binder tape are used to form a compact and reasonably circular
All armoured cables have extruded PVC bedding. The PVC used for bedding is
compatible with the temperature of Insulation material.
When armouring is required, the armour consists of single layer of Galvanised steel wire.
The armour is applied helical, with a left hand direction. We also provide other armours such as
steel strip, tape or tinned copper. Single core cables are armoured with Aluminium or copper
The standard cables are manufactured with Extruded black PVC Type-9 of B.S. 7655 or
ST-2 of IEC 60502. Outer sheath is embossed or printed with the information required by the
related standards. Special FR, FRLS compounds are used for outer sheathing of cables, to suit
customer’s specification requirements.
An extruded cable production line is a highly sophisticated manufacturing process that
must be run with great care to assure that the end product will perform reliably in service for
many years. It consists of many sub processes that must work in concert with each other. If any
part of the line fails to unction properly, it can create problems that will lead to poorly made
cable and will potentially generate many metres of scrap cable. The process begins when pellets
of insulating and semiconducting compounds are melted within the extruder. The melt is
pressurised and this conveys material to the crosshead where the respective cable layers are
formed. Between the end of the screw and the start of the crosshead.it is possible to place
meshes or screens, which act as filters. The purpose of these screens was, in the earliest days of
cable extrusion, to remove particles, or contaminants that might be present within the melt.
While still used today, the clean characteristics of today’s materials minimize the need for this
type of filter. In fact, if these screens are too tight, they themselves can generate contaminants in
the form of scorch or precross linking.
Nevertheless, appropriately sized (100 to 200-micron hole size) filters are helpful to
stabilize the melt and protect the cable from large foreign particles that most often enter from the
materials handling system.
The most current technology uses a method called a true triple extrusion process where
the conductor shield, insulation and insulation shield are coextruded simultaneously. The cables
produced in this way have been shown to have better longevity (Figure 3) . After the structure
of the core is formed the cable is crosslinked to impart the high temperature performance. When
a CV tube is used fine control of the temperature and residence time (linespeed) is required to
ensure that the core is crosslinked to the correct level.
In most MV, HV and EHV cable applications, the metal sheath/neutral is itself protected
by a polymeric oversheath or jacket. Due to the critical performance needed from the oversheath,
there are a number of properties that are required, such as good abrasion resistance, good
processability, reasonable moisture resistance properties, and good stress cracking resistance.
Experience has shown that the material with the best composite performance is a PE-based
oversheath, though PVC, Chlorosulfonated Polyethylene and Nylon have been used as jacket
Tests on XLPE cables retrieved after 10 years of operation show that the mean
breakdown strength falls by almost 50% (from 20 to 11 kV/mm – HDPE & PVC, respectively)
when PVC is used as a jacket material. Many utilities now specify robust PE based jackets as a
result. The hardness of PE is also an advantage when protection is required from termite damage.
Jackets extend cable life by retarding the ingress of water and soluble ions from the
ground, minimizing cable installation damage and mitigating neutral corrosion. Ninety three
percent of investor-owned utilities in the USA specify a protective jacket. The semiconductive
jacket or oversheath is recommended for high lightning incident areas or joint-use trenches
where telecommunications cables co-exist with power cables.
Inspection and Test Plan for Power Cable
The inspection and test plan for power cable article provides you information about power cable
test and power cable inspection in manufacturing shop.
Witnessing voltage and insulation resistance tests or alternative spark tests.
For 33Kv cable, witness dielectric power factor voltage test.
Dimensional checking on sample off-cut i.e. construction consistency, insulation
thickness, external sheath screen, armours and mans of main components.
Visual checking in respect of cable formation, core and external sheath colors, marking
Testing on material sample i.e. conductor coating, insulation external jacket for
elongation, heat strocle blending and characteristics of armour, metal and sheath
components including zinc coating.
Third Party Inspection for Power Cable Configuration
Third party inspector checks the power cable configuration in accordance to drawing and
datasheets. Following items is taken in account:
Number of conductors
Conductor color coding
Insulation type and size
Other specified elements/dimensions
References:Electrical Power Cable Engineering by Bruce S. Bernstein and William A. Thu
L.V. Power and Control Cables by Oman Cables Industry
TR-101670 ―Underground Transmission Systems Reference Book: 1992 Edition,‖
Electric Power ResearchInstitute
Technical specifications of cable work
This chapter covers the requirements for the selection, installation and jointing of
power cables for low, medium and high voltage applications upto and including 33KV.
For details not covered in these Specifications, IS:1255-1983 shall be referred to. All
references to BIS-Specifications and codes are for codes with amendments issued upto
date i.e. till the date of call of tender.
1.2 TYPES OF CABLES
1.2.1 The cables for applications for low and medium voltage (upto and including
1.1KV) supply shall be one of the following: (i) PVC insulated and PVC sheathed, conforming to IS:1554 (Part-1)- 1988
(ii) Cross linked polyethylene insulated, PVC sheathed (XLPE), conforming
to IS: 7098 (Part-1)- 1988.
1.2.2 The cables for applications for high voltage (above 1.1KV but upto and including
11KV supply) supply shall be one of the following: (i) PVC insulated and PVC sheathed, conforming to IS:1554 (Part-2)- 1988.
(ii) Paper insulated, lead sheathed (PILCA) conforming to IS:692-1973
(iii) Cross linked polyethylene (XLPE) insulated, PVC sheathed conforming to
IS:7098 (Part-2)- 1985.
1.2.3 The cables for applications above 11KV but upto and including 33KV supply
shall be one of the following: (i) Paper insulated lead sheathed (PILCA) conforming to IS: 692-1973.
(ii) Cross linked, polyethylene insulated (XLPE) conforming to IS:7098
1.2.4 The cables shall be with solid or stranded aluminium conductors, as specified.
Copper conductors may be used, only in special applications, where use of aluminium
conductors is not technically acceptable.
1.2.5 Where paper insulated cables are used in predominantly vertical situation, these
shall be of non-draining type.
1.3 ARMOURING AND SERVING
1.3.1 All multicore cables liable for mechanical damage and all HV cabkes
(irrespective of the situation of installation) shall be armoured. Where armouring is
unavoidable in dingle core cables, either the armour should be made of nonmagnetic
material, or it should be ensured that the armouring is not shorted at terminations, thus
preventing the flow of circulating currents therein.
1.3.2 Short runs of cables laid in pipes, closed masonary trenches and similar protected
or secured enclosures need not be armoured.
1.3.3 PVC and XLPE cables, when armoured, shall have galvanized steel wires (flat or
round) for armouring.
1.3.4 Paper insulated cables shall have for armouring, a double layer of steel tape for
normal applications. Steel wire armouring is preferred where the cables are liable to
tensile stresses in applications such as vertical runs, suspended on brackets or laid in
that is likely to subside.
1.3.5 Serving over armouring in paper insulated cables shall consist of a complete layer
or layers of suitable compounded Hessian materials.
1.4 SELECTION OF CABLE SIZES
1.4.1 The cable sizes shall be selected by considering the voltage drop in the case of
MV (distribution) cables and Current carrying capacity in the case of HV (feeder) cables.
Due consideration should be given for the Prospective short circuit current and the
of its flow, especially in the case of HV cables.
1.4.2 While deciding upon the cable sizes, derating factors for the type of cable and
depth of laying, grouping, ambient temperature, ground temperature, and soil resistivity
shall be taken into account.
1.4.3 Guidance for the selection of cables shall be served from relevant Indian
Standards such as IS:3961 (Part-1)-1967 for paper insulated lead sheathed cables, IS:
3961 (Part-2)-1967 for PVC insulated and PVC sheathed heavy duty cables, IS: 58191970 for recommended short circuit ratings of high voltage PVC cables, IS: 1255-1983
on code of practice for installation and maintenance of power cables upto and including
33KV rating etc.
1.5 STORAGE AND HANDLING
(i) The cable drums shall be stored on a well drained, hard surface, so that the
drums do not sink in the ground causing rot and damage to the cable drums. Paved
surface is preferred, particularly for long term storage.
(ii) The drums shall always be stored on their flanges, and not on their flat
(iii) Both ends of the cables especially of PILCA cables should be properly
sealed to prevent ingress/ absorption of moisture by the insulation during storage.
(iv) Protection from rain and sun is preferable for long term storage for all
types of cables. There should also ventilation between cable drums.
(v) During storage, periodical rolling of drums once in, say, 3 months through
90 degrees shall be done, in the case of paper insulated cables. Rolling shall be done in
the direction of the arrow marked on the drum.
(vi) Damaged battens of drums etc. should be replaced as may be necessary.
(i) When the cable drums have to be moved over short distances, they should
be rolled in the direction of the arrow marked on the drum.
(ii) For manual transportation over long distances, the drum should be
mounted on cable drum wheels, strong enough to carry the weight of the drum and
by means of ropes. Alternatively, they may be mounted on a trailer or on a suitable
(iii) For loading into and unloading from vehicles, a crane or a suitable lifting
tackle should be used. Small sized cable drums can also be rolled down carefully on a
suitable ramp or rails, for unloading, provided no damage is likely to be caused to the
cable or to the drum.
(i) Cables with kinks, straightened kinks or any other apparent defects like
defective armouring etc. shall not be installed.
(ii) Cables shall not be bent sharp to a small radius either while handing or in
installation. The minimum safe bending radius for PVC/XLPE (MV) cables shall be 12
times the overall diameter of the cable. The minimum safe bending radius for
PILCA/XLPE (HV) cables shall be as given in Table-II. At joints and terminations, the
bending radius of individual cores of a multi core cable of any type shall not be less than
15 times its overall diameter.
(iii) The ends of lead sheathed cables shall be sealed with solder immediately
after cutting the cables. In case of PVC cables, suitable sealing compound/tape shall be
used for this purpose, if likely exposed to rain in transit storage. Suitable heat shrinkable
caps may also be used for the purpose.
Before the cable laying work is undertaken, the route of the cable shall be decided
by the Engineer-in-Charge considering the following.
(i) While the shortest practicable route should be preferred, the cable route
shall generally follow fixed developments such as roads, foot paths etc. with proper
offsets so that future maintenance, identification etc. are rendered easy. Cross country
merely to shorten the route length shall not te adopted.
(ii) Cable route shall be planned away from drains and near the property,
especially in the case of LV/MV cables, subject to any special local requirements that
may have to be necessarily complied with.
(iii) As far as possible, the alignment of the cable route shall be decided after
taking into consideration the present and likely future requirements of other services
including cables enroute, possibility of widening of roads/lanes etc.
(iv) Corrosive soils, ground surrounding sewage effluent etc. shall be avoided
for the routes.
(v) Route of cables of different voltages.
(a) Whenever cables are laid along well demarcated or established roads, the
LV/MV cables shall be laid farther from the kerb line than HV cables.
(b) Cables of different voltages, and also power and control cables shall be
kept in different trenches with adequate separation. Where available space is restricted
such that this requirement cannot be met, LV/MV cables shall be laid above HV cables.
(c) Where cables cross one another, the cable of higher voltage shall be laid at
a lower level than the cable of lower voltage.
1.6.3 Proximity to communication cables
Power and communication cables shall as far as possible cross each other at right
angles. The horizontal and vertical clearances between them shall not be less than
1.6.4 Railway crossing
Cables under railway tracks shall be laid in spun reinforced concrete, or cast iron
or steel pipes at such depths as may be specified by the railway authorities, but not less
than 1m, measured from the bottom of the sleepers to the top of the pipe. Inside railway
station limits, pipes shall be laid upto the point of the railway station limits, pipes shall be
laid upto a minimum distance of 3m from the center of the nearest track on either side.
1.6.5 Way Leave
Way leave for the cable route shall be obtained as necessary, from the appropriate
(vi) Testing before covering
The cables shall be tested for continuity of cores and insulation resistance (Refer clause
2.8.1) and the cable length shall be measured, before closing the trench. The cable end
shall be sealed /covered as per clause 2.6.1 (iii)
(vii) Sand covering
Cables laid in trenches in a single tier formation shall have a covering of dry sand of not
less than 17cm above the base cushion of sand before the protective cover is laid.
In the case of vertical multi-tier formation, after the first cable has been laid, a sand
cushion of 30cm shall be provided over the base cushion before the second tier is laid.
additional tiers are formed, each of the subsequent tiers also shall have a sand cushion
30cm as stated above. Cables in the top most tiers shall have final sand covering not
than 17cm before the protective cover is laid.
Sand covering as per (a) and (b) above need not be provided for MV cables where a
decision is taken by the Engineer-in-Charge as per sub clause (i)(b) above, but the inter
tier spacing should be maintained as in (b) above with soft soil instead of sand between
tiers and for covering.
Sand cushioning as per (a) and (b) above shall however be invariably provided in the
of HV cables.
(viii) Extra loop cable
(a) At the time of original installation, approximately 3m of surplus cable shall be left
on each terminal end of the cable and on each side of the underground joints. The
cable shall be left in the form of a loop. Where there are long runs of cables such loose
cable may be left at suitable intervals as specified by the Engineer-in-Charge.
(b) Where it may not be practically possible to provide separation between cables
when forming loops of a number of cables as in the case of cables emanating from a
substation, measurement shall be made only to the extent of actual volume of
sand filling etc. and paid for accordingly.
(ix) Mechanical protection over the covering
(a) Mechanical protection to cables shall be laid over the covering in accordance with
(b) and (c) below to provide warning to future excavators of the presence of the cable
and also to protect the cable against accidental mechanical damage by pick-axe blows
(b) Unless otherwise specified, the cables shall be protected by second class brick of
nominal size 22cmX11.4cmX7 cm or locally available size, placed on top of the sand
soil as the case may be). The bricks shall be placed breadth-wise for the full length of
cable. Where more than one cable is to be laid in the same trench, this protective
shall cover all the cables and project at least 5cm over the sides of the end cables.
Engineer-in-Charge and generally at intervals not exceeding 100m. Markers shall also
provided to identity change in the direction of the cable route and at locations of
(ii) (a) Plate type marker
Route markers shall be made out of 100mm X 5mm GI/ aluminium plate welded / bolted
on 35mm X 35mm X 6mm angle iron, 60cm long. Such plate markers shall be mounted
parallel to and at about 0.5m away from the edge of the trench.
(b) CC marker
Alternatively, cement concrete 1:2:4 (1 cement:2 coarse sand: 4 graded stone
of 20mm in size) as shown in figure 2 shall be laid flat and centered over the cable. The
concrete markers, unless otherwise instructed by the Engineer-in-Charge, shall project
over the surrounding surface so as to make the cable route easily identifiable.
The words „CPWD-MV/HV CABLE‟ as the case may be, shall be inscribed on the
1.6.8 Laying in pipes / closed ducts
126.96.36.199 In locations such as road crossing, entry in to buildings, paved areas etc. cables
shall be laid in pipes or closed ducts. Metallic pipe shall be used as protection pipe for
cables fixed on poles of overhead lines.
(i) Stone ware pipes, GI, CI or spun reinforced concrete pipes shall be used for
cables in general; however only GI pipe shall be used as protection pipe on poles.
(ii) The size of the pipe shall not be less than 10cm in diameter for a single cable and
not less than 15cm for more than one cable.
(iii) Where steel pipes are employed for protection of single core cable feeding AC
load, the pipe should be large enough to contain both cables in the case of single phase
system and all cables in the case of poly phase system.
(iv) Pipes for MV and HV cables shall be independent ones.
(i) In the case of new construction, pipes as required (including for anticipated future
requirements) shall be laid alongwith the civil works and jointed according to the CPWD
(ii) Pipes shall be continuous and clear of debris or concrete before cables are drawn.
Sharp edges if any, at ends shall be smoothened to prevent damage to cable sheathing.
(iii) These pipes shall be laid directly in ground without any special bed except for SW
pipe which shall be laid over 10cm thick cement concrete 1:5:10 (1 cemtnt:5coarse
sand:10 graded stone aggregate of 40mm nominal size) bed. No sand cushioning or
need be used in such situations.
188.8.131.52 Road crossings
(i) The top surface of pipes shall be at a minimum depth of 1m from the pavement
level when laid under roads, pavements etc.
(ii) The pipes shall be laid preferably askew to reduce the angle of bend as the cable
enters and leaves the crossing. This is particularly important for HV cables.
(iii) When pipes are laid cutting an existing road, care shall be taken so that the soil
filled up after laying the pipes is rammed well in layers with watering as required to
ensure proper compaction. A crown of earth not exceeding 10cm should be left at the
(iv) The temporary re-instatements of roadways should be inspected at regular
intervals, particularly after a rain, and any settlement should be made good by further
filling as may be required.
(v) After the subsidence has ceases, the top of the filled up trenches in roadways or
other paved areas shall be restored to the same density and material as the
area in accordance with the relevant CPWD Building Specifications to the satisfaction of
184.108.40.206 Manholes shall be provided to facilitate feeding/drawing in of cables with
sufficient working space for the purpose. They shall be covered by suitable manhole
covers. Sizes and other details shall be indicated in the Schedule of work.
220.127.116.11 Cable entry into the building
Pipes for cable entries to the building shall slope downwards from the building. The
at the building end shall be suitably sealed to avoid entry of water, after the cables are
18.104.22.168 Cable-grip / draw-wires, winches etc. may be employed for drawing cables
through pipes / closed ducts.
22.214.171.124 Measurement for drawing/ laying cables in pipes/ closed duct shall be on the
of the actual length of the pipe / duct for each run of the cable, irrespective of the length
of cable drawn through.
1.6.9 Laying in open ducts
126.96.36.199 Open ducts with suitable removable covers (RCC slabs or chequered plates) are
generally provided in sub-stations, switch rooms, plant rooms, workshops etc. for taking
the cables. The cable ducts should be of suitable dimensions for the number of cables
(i) Laying of cables with different voltage ratings in the same duct shall be avoided.
Where it is inescapable to take HV & MV cables same trench, they shall be laid with a
barrier between them or alternatively, one of the two (HV &MV) cables may be taken
(ii) Splices or joints of any type shall not be permitted inside the ducts.
(i) The cables shall be laid directly in the duct such that unnecessary crossing of
cables is avoided.
(ii) Where specified, cables may be fixed with clamps on the walls of the duct or
taken in hooks/brackets/troughs in ducts.
Where specified, ducts may be filled with dry sand after the cables are laid and covered
as above, or finished with cement plaster, specially in high voltage applications.
Laying on surface
This method may be adopted in places like switch rooms, workshops, tunnels, rising
(distribution) mains in buildings etc. This may also be necessitated in the works of
additions and/or alterations to the existing installation, where other methods of laying
may not be feasible.
Cables may be laid in surface by any of the following methods as specified:
(a) Directly clamped by saddles or clamps,
(b) Supported on cradles,
(c) Laid on troughs/trays, duly clamped.
(i) The saddles and clamps used for fixing the cables on surface shall comply with
the requirements given in Table-III.
(ii) Saddles shall be secured with screws to suitable approved plugs. Clamps shall be
secured with nuts on to the bolts, grouted in the supporting structure in an approved
(iii) In the case of single core cables, the clamps shall be of non-magnetic material. A
suitable non-corrosive packing shall be used for clamping unarmoured cables to prevent
damage to the cable sheath.
(iv) Cables shall be fixed neatly without undue sag or kinks.
The arrangement of laying the cables in cradles is permitted only in the case of cables
1.1KV grade of size exceeding 120sq.mm. In such cases, the cables may be
MS flat cradles of size 50mmX5mm which in turn shall be fixed on the wall by bolts
grouted into the wall in an approved manner at a spacing of not less than 60cm.
All MS components used in fixing the cables shall be either galvanized or given a coat
red oxide primer and finished with 2 coats of approved paint.
1.6.11 Laying on cable tray
This method may be adopted in places like indoor substations, air-conditioning plant
rooms, generator rooms etc. or where long horizontal runs of cables are required within
the building and where it is not convenient to carry the cable in open ducts. This method
is preferred where heavy sized cables or a number of cables are required to be laid.
cable trays may be either of perforated sheet type or of ladder type.
188.8.131.52 Perforated type cable tray
(i) The cable tray shall be fabricated out of slotted/perforated MS sheets as
channel sections, single or double bended. The channel sections shall be supplied in
convenient lengths and assembled at site to the desired lengths. These may be
galvanished or painted as specified. Alternatively, where specified, the cable tray may
fabricated by two angle irons of 50mmX50mmX6mm as two longitudinal members, with
cross bracings between them by 50mmX5mm flats welded/bolted to the angles at 1 m
spacing. 2mm thick MS perforated sheet shall be suitably welded/bolted to the base as
well as on the two sides.
(ii) Typically, the dimensions, fabrication details etc. are shown in figure
3A,B and C.
(iii) The jointing between the sections shall be made with coupler plates of the
same material and thickness as the channel section. Two coupler plates, each of
200mm length, shall be bolted on each of the two sides of the channel section with 8mm
dia round headed bolts, nuts and washers. In order to maintain proper earth continuity
bond, the paint on the contact surfaces between the coupler plates and cable tray shall
scraped and removed before the installation.
(iv) The maximum permissible uniformly distributed load for various sizes of
cables trays and for different supported span are given in Table IV. The sizes shall be
specified considering the same.
(v) The width of the cable tray shall be chosen so as to accommodate all the
cables in one tier, plus 30 to 50% additional width for future expansion. This additional
width shall be minimum 100mm. The overall width of one cable tray shall be limited to
(vi) Factory fabricated bends, reducers, tee/cross junctions, etc. shall be
provided as per good engineering practice. (Details are typically shown in figure 3). The
radius of bends, junctions etc. shall not be less than the minimum permissible radius of
bending of the largest size of cable to be carried by the cable tray.
(vii) The cable tray shall be suspended from the ceiling slab with the help of
10mm dia MS rounds or 25mmX5mm flats at specified spacing (based on Table III). Flat
type suspenders may be used for channels upto 450mm width bolted to cable trays.
Round suspenders shall be threaded and bolted to the cable trays or to independent
support angles 50mmX50mmX5mm at the bottom end as specified. These shall be
grouted to the ceiling slab at the other end through an effective means, as approved by
Engineer-in-Charge, to take the weight of the cable tray with the cables.
(viii) The entire tray (except in the case of galvanized type) and the suspenders
shall be painted with two coats of red oxide primer paint after removing the dirt and rust,
and finished with two coats of spray paint of approved make synthetic enamel paint.
(ix) The cable tray shall be bonded to the earth Terminal of the switch bonds at
(x) The cable trays shall be measured on unit length basis, along the center
line of the cable tray, including bends, reducers, tees, cross joints, etc. and paid for
184.108.40.206 Ladder type cable tray
(i) The ladder type of cable tray shall be fabricated of double bended channel
section longitudinal members with single bended channel section rungs of cross
welded to the base of the longitudinal members at a center to center spacing of 250cm.