NIE Basic Electrical Engineering Unit 6

2. ELECTRICAL WIRING
 Electrical wiring is generally refers to insulated
conductor used to carry current and associated device.
 Domestic electric appliances like lights, fans, washing
machines, water pumps etc are connected to the supply
through insulated wires which are controlled by switches.
 The wiring diagram gives the connections of different
appliances to the supply within a house or building.

3. Service Connection
 The electric service utility or the
distribution company supplies power
to domestic consumers.
 The line which brings the supply from
the distributor transformer to the
consumer’s meter is called the service
connection.
 The live wire or neutral wire are
incoming wires from the utility(single-
phase or three-phase).

5. Wiring & its types
 Wires are drawn along the consumer’s
building to distribute power to all
points where load is situated.
 Types of wiring according to uses;
o Domestic wiring.
o Commercial wiring.
o Industrial wiring.

6. FACTORS AFFECTING THE CHOICE OF
WIRING
 Durability : Type of wiring selected should conform to
standard specifications, so that it is durable i.e. without
being affected by the weather conditions, fumes etc.
 Safety : The wiring must provide safety against leakage,
shock and fire hazards for the operating personnel.
 Appearance : Electrical wiring should give an aesthetic
appeal to the interiors.
 Cost: It should not be prohibitively expensive.
 Accessibility : The switches and plug points provided
should be easily accessible. There must be provision for
further extension of the wiring system, if necessary.
 Maintenance Cost : The maintenance cost should be a
minimum.
 Mechanical safety : The wiring must be protected
against any mechanical damage.

7. Types of Wiring
 Cleat wiring
 CTS wiring or TRS wiring or Batten
wiring
 Metal sheathed wiring or lead
sheathed wiring
 Casing and capping
Conduit wiring

8. Cleat wiring
This System uses insulated Cables sub protected in
porcelain cleats.

9. CTS wiring or TRS wiring or
Batten wiring

10. Metal sheathed wiring or lead
sheathed wiring

11. Casing and capping
A rectangular strip of wood called
capping having same width as that of
casing is fixed over it. Both the
casing and the capping are screwed
together at every 15 cms. Casing is
attached to the wall.

12. Conduit wiring
 This type of wiring is most popular in
domestic applications.
 Conduits are normally made of
galvanized steel or PVC.
 Conduits are tubing systems for
protection and routing of wiring.
 Conduits may run over the surface of
the walls & ceiling or may be
concealed under masonry work.

13. Advantages

16. Wiring schemes
 Control with one switch
 Two way control of lamps
 Three way control of lamps
i) Control with one switch:

17. ii) Two way control of lamps
S1 S2 Lamp
1 1 ON
1 2 OFF
2 1 OFF
2 2 ON
1
1
2
1
1
2

18. iii) Three way control of lamps
•By suitably throwing the switches to different positions , the lamp
can be controlled by using all switches.
•This connection is commonly used when the switches are in
three different locations.
•For ex: the lamp could be in the second floor and the switches in
1,II & III floors. The lamp could be in the centre of a long corridor
and the switches in the beginning, centre and the end of the
corridor.

19. Fuses
 Is one of the most inexpensive ways of
protecting an equipment.
 The fuse wire melts when excess current
flows through it and cuts off the supply to
the equipment.
 Used in both high & low voltage circuits

20. Desirable properties of fuse link
 High conductivity
 Free from oxidation
 Low resistance
 Low cost
 Low melting point
 Common materials used are lead,
tin,zinc & silver.
 It can carry normal current
continously.

21. Terms related to fuse
 Ampere rating
 Voltage rating
 Breaking current
 Fusing current
 Fusing factor
 Prospective short circuit current
 Cut-off current
 Fuse base and carrier
 Pre arcing time
 Arcing time
 Total operating time

22. Different types of fuses
 Semi-enclosed or rewirable fuse:
commonly used in domestic installations. It
consists of a porcelain base which carries the
terminals.
 Cartridge fuse: In this type the fuse element is
placed in a totally enclosed fuse carrier with two
metal contacts on either side.
 High rupturing capacity(HRC) fuse:
These fuses are used for higher currents. It
consists of a heat resistant ceramic body having
metal end caps welded to silver fuse element. The
space inside is filled with quartz powder, which
helps in extinguishing the arc.

23. Contd…
 Semi-enclosed or rewirable fuse
 Cartridge fuse
 High rupturing capacity(HRC) fuse

24. Contd…
Advantages
 It is the cheapest form of protection
 Requires no maintenance.
 Can interrupt large currents without noise, flame or
smoke.
 Does not require a fault detecting device.
Disadvantages
 It has to be replaced every time it blows off.
 In three-phase circuits, even if fuse blows off in one
phase, all three fuses must be replaced.

25. Miniature circuit breaker(MCB)
 Is a device designed to isolate a circuit
during an over current occur without
the use of a fusible element.
 A circuit breaker is an automatically
operated electrical switch designed to
protect an electrical circuit from
damage caused by overload or
short circuit. Its basic function is to
detect a fault condition and interrupt
current flow.

26. Application of MCB’s
Domestic appliances, power supplies, lighting
circuits ,motor circuits, relay/contactor coils
Advantages of MCB
 Stable tripping characteristic
 Closed overload protection
 Common tripping for all phases in case of three
phase application
 Instant reclosing after fault has been cleared
Disadvantage of MCB
 More expensive than fuse
 Difficult to identity fault location
 Large amount of energy

27.  An electric shock (electrocution)occurs when two portion of a
person’s body come in contact with electrical conductors of a
circuit which is at different potentials, thus producing a
potential difference across the body.
 The human body does have resistance and when the body is
connected between two conductors at different potential a
circuit is formed through the body and current will flow
 When the human body comes in contact with only one
conductor, a circuit is not formed and nothing happens. When
the human body comes in contact with circuit conductors, no
matter what the voltage is there is potential for harm.
Electric shock

28.  The higher the potential difference the more
the damage. The effect of an electric shock is a
function of what parts of body come in contact
with each conductor, the resistance of each
contact point the surface resistance of the body
at the contact as well as other factor.
 When the electrical contact is such that the
circuit path through the body is across the
heart, you have the greatest potential for death.
Electric shock

29. How to handle electric shock
victims?
 The first thing to do is to disconnect
the power supply
 Donot even touch the victim untill the
supply is off
 Be care full especially in wet area.

30. What Is Earthing
The process of connecting metallic bodies
of all the electrical apparatus and
equipment to huge mass of earth by a wire
having negligible resistance is called
Earthing.

31. • Provide an alternative path for the fault
current to flow so that it will not
endanger the user
• Ensure that all exposed conductive parts
do not reach a dangerous potential
• Maintain the voltage at any part of an
electrical system at a known value so as to
prevent over current or excessive voltage
on the appliances or equipment.

32. Qualities Of Good Earthing
 Must be of low electrical resistance
• Must be of good corrosion resistance
• Must be able to dissipate high fault
current repeatedly

33. Purpose of Earthing
• To save human life from danger of electrical shock or death by
blowing a fuse i.e. To provide an alternative path for the fault
current to flow so that it will not endanger the user
• To protect buildings, machinery & appliances under fault
conditions ie. To ensure that all exposed conductive parts do not
reach a dangerous potential.
• To provide safe path to dissipate lightning and short circuit currents.
• To provide stable platform for operation of sensitive electronic
equipments i.e. To maintain the voltage at any part of an electrical
system at a known value so as to prevent over current or excessive
voltage on the appliances or equipment .
• To provide protection against static electricity from friction

34. Methods of Earthing
 Conventional Earthing
 Maintenance Free Earthing

35. Conventional Earthing
 The Conventional system of Earthing calls
for digging of a large pit into which a GI
pipe or a copper plate is positioned in the
middle layers of charcoal and salt.
 It requires maintenance and pouring of
water at regular interval.

36. CONVENTIONAL
EARTHING

37. Maintenance Free Earthing
• It is a new type of earthing system which is
Readymade, standardized and scientifically developed.
Its Benefits are
• MAINTENANCE FREE: No need to pour water at
regular interval- except in sandy soil.
• CONSISTENCY: Maintain stable and consistent earth
resistance around the year.
• MORE SURFACE AREA: The conductive compound
creates a conductive zone, which provides the increased
surface area for peak current dissipation. And also get
stable reference point.

38. Maintenance Free
Earthing(Contd.)
 LOW EARTH RESISTANCE: Highly
conductive. Carries high peak current
repeatedly.
 NO CORROSION:
 LONG LIFE.
 EASY INSTALLATION.

39. Methods of Conventional Earthing
1. Plate Earthing
2. Pipe Earthing
3. Rod Earthing
4. Strip Earthing
5. Earthing through Water Mains

40. Earthing Electrode
The resistance of a ground
electrode has 3 basic
components:
A) The resistance of the ground
electrode itself and the connections
to the electrode.
B) The contact resistance of the
surrounding earth to the electrode.
C) The resistance of the surrounding
body of earth around the ground
Electrode. It consist of three basic components:
1. Earth Wire
2. Connector
3. Electrode

41. Plate Earthing
 In this type of earthing plate either of copper or of
G.I. is buried into the ground at a depth of not less
than 3 meter from the ground level.
 The earth plate is embedded in alternative layer of
coke and salts for a minimum thickness of about
15cm.
 The earth wire(copper wire for copper plate
earthing and G.I. wire for G.I. plate earthing) is
securely bolted to an earth plate with the help of
bolt nut and washer made of copper, in case of
copper plate earthing and of G.I. in case of G.I.
plate earthing.

42. PLATE EARTHING

43. Pipe earthing
 Pipe earthing is best form of earthing and it is cheap also in this system
of earthing a GI pipe of 38 mm dia and 2meters length is embedded
vertically in ground to work as earth electrod but the depth depend upon
the soil conditions, there is no hard and fast rule for this.
 But the wire is embedded upto the wet soil.
 The earth wire are fastened to the top section of the pipe with nut and
bolts.
 The pit area arround the GI pipe filled with salt and coal mixture for
improving the soil conditions and efficiency of the earthing system.
 It can take heavy leakage current for the same electrode size in
comparison to plate earthing.
 The earth wire connection with GI pipes being above the ground level
can be checked for carrying out continuity test as and when desired,
while in plate earthing it is difficult.
 In summmer season to have an effective earthing three or four bucket of
water is put through the funnel for better continuity of earthing.

44. PIPE EARTHING