Main parts of cables and types of cables

1. Elements of Electrical Engineering (2110005)
Guided by :
Prof. Anand .C. Patel
Created By :
Name : Shah Preet .P.
Enroll. No. : 160410119117
Batch : C
Dept : Mechanical
Topic : Types Of Cables
1

2. Cables
A cable is made up of several wires stranded together. The main
functions of a cables are as follow:
1. It should conduct electricity efficiently, cheaply ans safely.
2. Its size must not be so small that the internal voltage drop
becomes high.
3. Its size should not be so large that its cost rises enormously.
4. Its insulation must be sturdy so that there is no unwanted
leakage current.
2

3. Sections
A cable has three sections:
1. Core : A metal wire or strand of
wires carrying the current.
2. Insulation : A covering of
insulation or dielectric material
to prevent leakage of current
from the conductors.
3. Cover : A covering to protect
the insulation from any
damage.
3

4. Conductor
 The conductor or core of the cable carries
the current.
 They are made up of copper and
aluminium.
 Copper has higher electrical conductivity,
mechanically strong, durable and ductile.
 It can nicely withstand corrosion, oxidation,
pitting, dampness and high temperature.
 It can be easily soldered and welded. It
has a melting point of 1083˚C.
4

5.  Aluminium is cheaper than copper. So
it is used for long distance power
distribution.
 However its electrical conductivity,
tensile strength and melting point is
less than that of copper.
5

6. Insulators
 The insulation or dielectric should be highly
resistive to the flow of current, thus ensuring
minimum risk of shock and fire.
 The insulation material used must have
following properties:
1. High resistivity
2. High flexibility
3. High dielectric strength
4. High resistance to moisture, acids etc.
5. Non inflammability
6. Withstand capability for high rupturing
voltages without deterioration
6

7.  Some of widely used dielectrics are
rubber, vulcanised rubber,
impregnated paper, varnished
cambric, PVC, vulcanised bitumen,
gutta percha, silk and cotton, enamel
etc.
 The material used depend upon the
service for which cable is being used.
7

8. Cover
 A protective cover is provided over the
insulation to prevent any mechanical
damage. If the cable is straight, steel
tapes may be used.
 But such a cover will not allow
bending of the cables. If the cable is to
be bent, steel wire armouring is used.
 Normally a single layer of armouring is
sufficient. However double layer is
preferred as it provides greater
flexibility.
8

9.  For ordinary main cables, an
aluminium sheathing is provided which
has a tight covering of materials like
PVC, such cables need no armouring.
 All cables are provided with an
additional external covering for
protection against damage and
moisture.
9

10. Types Of Cables
 Cables are classified mainly according to :
1. Conductor used
2. Type of insulation
3. Voltage grading
4. Number of cores
• The cables are divided into two groups based
on the voltage grading
1. 250/440 V Cables
2. 650/1100 V Cables.
10

11.  Depending upon the number of
strands, cables are classified as :
1. Two core
2. Three core
3. Three and a half core
4. Four core cables or even more
11

12. Two And Three Core Cables
 In a two core cable one
strand is for phase and the
second for the neutral.
 Both strand have equal cross
sectional area.
 Similarly in three core cables
also have equal cross
sectional area.
 The three strand carry R, Y &
B phases respectively.
12

13. Three and Half And Four Core
Cables
 In three and half core cables as well
as four core cables there are three
strands of equal cross sectional area
for R,Y & B phases respectively.
 The last strand is for neutral. Normally
under balanced load the neutral will
not carry any current.
 In cases where probability of fault or
unbalanced load is high, the neutral
will carry current.
13

14.  In three and a half core cable,
the strand for the neutral has
cross-sectional equal to half that
of the other three strands.
 This is done to bring down the
cost of the cable because as
already mentioned the neutral
carries current only under faulty
or unbalanced load conditions.
 A four core cables has all four
strands of equal cross section
area. They are used for lighting,
load distribution and applications
where unbalanced loading
conditions occur frequently.
14

15.  Multi strand cables are more durable. They
are more flexible and hence are easier to
handle.
 As compared to single core cables, multi core
cables have more surface area and therefore
their cooling or heat radiating capacity is
more.
15

16. Thank You
16