CHAPTER TWO

WIRING MATERIALS AND INSTALLATION

ACCESSORIES

2.1. Wiring materials and Conduits

2.2. Electrical installation materials, components and accessories

2.3. Electrical regulations, standards and symbols

1
 2.1. Wiring materials and Conduits

• In order to assemble available electrical materials, devices, fittings and

equipment to form a complete wiring system, we must understand the

basic principles and characteristics regarding them.

• The major components of any electrical installation are

Wire/Cable

Conduits

Electrical Junction Boxes

Circuit Breaker and fuse

Distribution Board
2
 2.1.1. Wires and Cables
The term wire and cable are used more or less synonymously
 Wire: is a single conductor, may be bare or covered with insulation is known
as a wire. Cable: several wires stranded together is known as a cable
 In practice bare conductors, whether single or stranded together are termed
as Wire. And Conductors covered with insulation are termed as cables.

The necessary requirements of a wire/cable are that it should conduct electricity

 efficiently,

cheaply, and

 safely

With less voltage drop

3
 Parts of a Cable
A cable consists of three parts:
The conductor or (the core): -the metal wire or strand of wires
caring current.
The insulation or the dielectric: -is an insulating material to
avoid leakage current from the conductor.
The protective covering: -is used for protection of insulation
from mechanical damage.

4
 a. Conductor materials used in cable
• Conductor (of cable) is a part of a cable which has the specific
function of carrying current
• A conductor is either solid (i.e. a conductor consisting of a single
wire) or stranded (i.e. a conductor consisting of a number of
individual wires, all or some of which generally have a helical
form).
• Copper and aluminum are the materials most commonly used as
conductors in power and lighting cables.
• silver is the best conductor, but due to its higher cost it is hardly
used anywhere.
5
 Cont.
• The next best conductor is copper, which is comparatively cheap.
 It is mechanically strong, hard, extremely tough, durable and
ductile.
 It is highly resistive to corrosion, oxidation, and pitting and
has resistivity of 1.786 x 10-8 ohm.m at 200c temperature.

• Aluminum: is frequently used in place of copper for bare

electric conductors used for long distance power distribution.

6
 Cont.
• The electrical conductivity of aluminum is about 60% of that of

copper and it has the electrical resistivity of pure aluminum at 20 0c

is 2.6 x 10-8 ohm.m.

• The only application of aluminum cables for wiring in buildings is

for a continuous bus-bar system of distribution.

• One of the most important advantages of aluminum is its low

density. A unit length of bare aluminum wire weighs only 48% as

much as the same length of copper wire having an equivalent dc

resistance.
7
 Cont.
• The size of conductors shall be such that

 the voltage drop between the supply terminal and fixed current-using

equipment shall not exceed 4% of the nominal voltage of the supply line

when the conductors are carrying the full load current.

• The minimum size(cross sectional area) of conductor :

 1.0mm2 for cables and insulated copper conductors for power and

lighting circuits;

 10.0mm2 for bare copper conductors for power circuits;

 16.0mm2 for bare aluminum conductors for power circuits;

 0.5mm2 for flexible cables of copper conductors for extra low voltage
8
 b. Insulating Materials
 Insulation used to prevent leakage of current in unwanted direction and to

minimize risk of fire and shock.

 The materials which have very high resistivity i.e. offers a very high

resistance to the flow of electric current.

 Insulating materials plays an important part in various electrical and

electronic circuits.

 In domestic wiring insulating material protect us from shock and also prevent

leakage current.

 So insulating material offers a wide range of uses in engineering applications.

9
 Cont.
 The insulating material used in electrical cable must posses the

following properties.

• High resistivity,

• High flexibility,

• Non-inflammability and

• High resistivity to moisture ,acid or alkali etc…..

 The type of insulating material used depends on the service for

which the cable is required.

10
 Cont.
The various types of insulting materials used are :-

1. Rubber

2. PVC (Polyvinyl chloride)

3. Vulcanized India Rubber(VIR)

4. Impregnated Paper

1.Rubber:-it may be natural or synthetic and its dielectric strength is

30kv/mm.

Though it posses high insulating qualities,

it absorbs moisture readily,

softens at a temperature of 600c to 700c, 11

 Cont.

2. PVC (Polyvinyl chloride): Polyvinyl Chloride is a man-made

thermo-plastic material, which is tough, incombustible and chemically

unreactive.

 Its chief drawback is that it softens at a temperature above 800c.

 It does not deteriorate with age and does not need to be renewed.

 PVC insulated cables are usually employed for low and medium

voltage domestic and industrial lights and power installation.

12
 Cont.
3. Vulcanized India Rubber(VIR): It is prepared by
mixing Indian rubber with minerals such as Sulphur, zinc,

red lead, etc.

• The copper conductors used in this cables are tinned to

protect them from corrosive action of rubber or copper.

• It absorbs water, which reduces its insulation properties and

becomes brittle with age.

• The use of VIR cables is limited to low voltage distribution

13
 Cont.
4. Impregnated Paper:-it is quite cheap, has low capacitance, high
dielectric strength (30KV/mm), and high insulation resistivity

(10Mohm-cm).

• The main advantage of paper insulated cable is that a cable of given

size can be worked out at a higher current density than a VIR cable.

• Impregnated paper insulated cable on its own would be too fragile to

be used unprotected, and a lead sheath is applied over the insulation.

• it used for conveying large power in transmission and distribution

and particularly for distribution at low voltage in congested areas .

14
 C. Mechanical protection

• Since all the insulating materials used in the manufacturing

of cables are mechanically weak, they require some form of
protection for mechanical injury.

• Mechanical protection is usually provided to power cables

laid direct in the ground by providing two layers of steel tape
in such away that upper layer covers the lower joint in the
lower layer.

15
 Types of Cables used in internal wiring

• The wires used for internal wiring of buildings may be divided in to

different groups according to:-

1.The type of conductor

2.The number of cores

3.The voltage grading

4.The type of insulation used.

• According to the number of cores, the cables may be divided in classes

known as single core, twin core, and twin core with ECC (earth

continuity conductor). 16
 Cont.
• According to voltage grading the cables may be divided in to
two classes: 250/440 volt and 650/1100-volt cable.

• According to types of insulation cables can be classified in to

1. vulcanized Indian rubber(VIR) cables

2. PVC cables

3. Lead sheathed cables

4. Weather proof cables

5. Flexible cords and cables

17
 Cont.
1. Vulcanized Indian Rubber (VIR) cables:-VIR cables are
available in 250/440volt as well as 650/1100 volt grades and are
used for general conduit wiring.
2. PVC cables: PVC cables are available in 250/440 volt and
650/1100 volt grades and used in concealed type of wiring
system. Since PVC cables are harder than rubber, they do not
require cotton taping and braiding over it for mechanical and
moisture protection.

18
 Cont.
3. Lead sheathed cables: it is available in 250/440 volt grade

are used for internal wiring where climatic condition has moisture.
• Is a vulcanized rubber insulated conductor covered with a
continuous sheath of lead .
• The sheath provides very good protection against the absorption of
moisture and sufficient protection against mechanical injury and
can be used with out casing or conduit system.
• It is available as single core, flat twin core, flat three core and flat
twin core with ECC.
19
 Cont.

4. Weather proof cables:-Are used for out door wiring

and for power supply
• They are not affected by heat or sun or rain.
• They are available in 250/440 and 650/1100 volt grades.
• They are either PVC insulated or vulcanized rubber-
insulated conductors being suitably taped (only incase
of vulcanized rubber insulated cable) braided and then
compounded with weather resisting material.
20
 Cont.
5. Flexible cord cables:-It consists of wires either silk or cotton or plastic
covered.

• Plastic cover is more popular as it is available in various pleasing colors.

• Flexibility and strength is by using conductors having large number of

strands.

• Most stranded conductors are built upon a single central conductor,

surrounding this conductor are layers of wires in a numerical progression
of 6 in the first layer, 12 in the second layer, 18 in the third layer and so
on.

21
 General Specification of cables
 The complete specification of a cable will give the
following information:-
i. The size of the cable.
ii. The type of conductor used in the cable(Copper or
Aluminum).
iii. Number of cores that the cable consists of (single, twin core,
twin core with ECC).
iv. Voltage grade.
v. Type of insulation
22
Factors Affecting Selection Of an Insulating Material

1. Operating condition : Before selecting an insulating

material for a particular application the selection should

be made on the basis of operating temperature, pressure

and magnitude of voltage and current.

2. Easy in shaping : Shape and size is also important affect.

3. Availability of material : The material is easily available.

4. Cost : Cost is also a important factor.

23
 Insulating Materials General Properties

The properties can be classified as

 Electrical properties.

Thermal properties.

Chemical properties.

 Physical/Mechanical properties

Reading Assignment
24
 Cont.
Electrical properties.

The insulation material must possess the following

Electrical properties:
 High resistivity

 High flexibility

 Non- inflammability

 High resistivity to moisture, acids and alkaline materials

25
 2.1.2. Conduits
• Electric Conduits are the pipelines (metal or plastic) that are

used to protect wires/cables from mechanical damage and

ensure safety wiring of electrical wire or cable in building

electrical installation

• They allow threading or changing electrical wire or cable.

• Adjacent or parallel conduits cast in concrete shall be

separated by a spacing of not less than 25mm so as to allow

concrete aggregate to pass & set between them.

26
 Cond.
• In general, the types of conduit used in electrical
installation work are as follows: :

i. Light gauge steel-plain (unscrewed) conduit.

ii. Heavy gauge steel-screwed conduit.

iii. Flexible conduit
iv. PVC conduit.

27
 i. Light gauge steel conduit

• This type of conduit is used with special grip fittings.

• It is available with an external diameter of 12mm, 16mm,

19mm, 25mm, 31mm, 38mm, and 50mm.
• In general, light gauge is the cheapest and quickest of
conduit installations but should be used at road crossing
and where the location is dry and there is little likelihood
of mechanical damage.
• It is available up to 6 meters
28
 ii. Heavy gauge screwed steel conduit:
• Though it is very expensive, this type of conduit provides a
permanent installation with a maximum of protection for the
cables.
• It is a rigid type conduits
• The joints into fittings are by means of screw threads which
provide mechanical strength and good electrical conduit.
• These conduits are available in approximately 20meter lengths
and are threaded at the two ends.

29
 iii. Flexible steel conduit
It consists of light galvanized steel strip spirally wound, and to some
extent, interlocked, so as to form a tube.

It is made in size from 19mm to 50mm internal diameter and in two

grades: non water tight and water tight.

They are available in lengths up to 250 meters. So no coupling is required

and hence no threading. Since the conduits are flexible and are easily bent

no elbow is required.
common used for protecting the final connections of motors.

It has the additional advantage of reducing the transmission of vibration.

However, the flexible conduit is costlier than the rigid conduit. 30

 vi. PVC
• The basic material is poly-vinyl-chloride (PVC) which is produced in both
flexible and rigid forms.

• PVC conduit is not suitable for installations subject to temperatures below -5oC
or above 65oC.

Advantages of PVC Conduit

Light weight and easy to handle

Easy to cut and debut

Simple to form and bend

Does not require painting

Minimal condensation due to low thermal conductivity in wall of conduit.

Speed of installation

Excellent electrical and fire resistant properties 31

 Cont.
Disadvantages of PVC Conduit
Care must be taken when gluing joints to avoid forming a barrier
across the inside of the conduit.

If insufficient adhesive is used the joints may not be waterproof.

PVC expands about 5 times as much as steel and this expansion

must be allowed for.

PVC does not offer the same level of mechanical protection as steel.

A separate Circuit Protective Conductor must be run inside the

conduit

32
 Conduit wiring
• There are three types of conduit wiring

 Flexible conduit wiring

 Surface conduit wiring

 Concealed conduit wiring

a. . Flexible conduit wiring:

•The flexible conduit pipe is a pipe which can bend or twist without change in

diameter.

• It is used where straight run of rigid conduit is not possible or where the

wires are to be bent and twisted so many times.

•The flexible conduits are not used for general electrical wiring system.

33
 Cont.
b. Surface conduit wiring: The conduit in surface conduit wiring is placed on

the surface of the wall with the help of saddles.

•This wiring system is applied in industrial wiring.

•It is very rarely used in domestic wiring as it does not give a good look

c. Concealed conduit wiring: The conduits are embedded along walls or ceiling

in plaster at the time of construction.

•The cables are drawn into the conduits after conduits are placed in walls and

wall slots plastered and dried.

•The wires are pulled into the conduits by means of steel wire.

•The conduit should be electrically and mechanically continuous and connected

to earth at some suitable place through the earth wire. 34

 Conduit Accessories and Fittings
Conduit Couplers: Couplers are used to join two lengths of

conduit. The screwed conduit are always threaded at both ends

on the outer side.

Conduit Bends, Elbows and Tees: In general conduit fittings

include bends, elbows and tees

Bends are usually used for change in direction of conduit.
This should never be sharp. The minimum allowable radius
of curvature is 2.5 times the outside diameter of the conduit.
Solid elbows and tees should be used only at the end of the
conduit run (e.g. close behind a light fitting or accessory.)
Conduit shall not be bent with an acute angle.

35
 Cont.
• Conduit boxes:
used in surface conduit wiring as well as concealed conduit wiring.

are of different designs which serve the following purposes:

• For providing connections to light, fan, and other points. Outlet box/Terminal box

The conduit boxes serving this purpose are known as outlet

boxes because conduit terminates at the boxes.

• For pulling of cables in to the conduits.. The boxes serving

this purpose are known as inspection boxes.
Inspection box
• For housing junction of cables. The conduit boxes serving
this purpose are known as junction boxes.

36
 Cont.
Conduit bushings:
• These are used when rigid conduit enters the conduit box or
switch board. It is also placed when the conduit enters a hole in
the switch board or conduit box which is not threaded.
• The bushing serves two purposes.
 Firstly it prevents the insulation of cables from getting injured.
 Secondly it helps in securing the rigid conduit with conduit
box

37
 Cont.
Lock nuts: When box connection with rigid conduit

is made, it is necessary that the lock nut should be

screwed on the conduit end in box as it makes the
connection completely rigid and electrically
continuous.

• The lock nuts are formed out of thin steel metal

sheet with outer side octal and inner hole
threaded as standard pipe.

Inspection elbow (Screwed): the inspection elbow

is used where right angle run of conduit bends is
required regularly
38
 2.2. Electrical installation materials,
components and accessories
The materials that are used in Electrical installation are,

Switches

Lamp Holder

Plugs and socket outlets:

Fuse and Circuit Breaker

Distribution board

39
  Switches:
 Are used to control lighting circuits.

 Most are rated at 5/6A, but ratings at 15A are also available.

 Are available in three types: single pole, two-way and four-way

(intermediate) each for control of a practical circuit arrangement.

 To allow true control of a number of different circuits from one

position, switches are contained within the same unit: two-gang, six-

gang, etc.

40
 Cont.
 Switches for water-heaters are of the double pole type and rated

to carry 20A. Are also available at 32A and 45A rating, the latter

being used to control cooker circuits.

 Dimmer switches are used to allow control of the level of

lighting from luminaries.

 Splash-proof switches are found in situations where water is

present, such as in shower rooms.

41
  Lamp Holders
 Are designed for quick removal
and replacement of the lamp and
yet they must hold the lamp in firm
metallic contact to prevent
overheating.
 There are three main sizes of lamp
holders:
 Bayonet-cap (B.C),

 medium Edison screw (E.S)

 Goliath screw (G.E.S).

42
 Cont.
 For ordinary tungsten filament lamps up to 200W the lamp
caps and lamp holders are B.C caps, up to 300W the caps are
E.S, and above 300W they are G.E.S.

 In any case where the lamp is to be installed, the appropriate

size and type of holder must be fitted.

 Lamp holders may be either the insulated type of Bakelite or

the brass type with porcelain interior.

43
  Plugs and socket outlets:
 These are used to enable portable apparatus to be connected to the

fixed wiring and comprises of two or three contact tubes and terminals.

 The plug is the movable part connected to the apparatus by flexible

wire, and consists of two or three contact pins to fit in to the contact

tubes.

44
  Fuse and circuit breakers
 Designed to interrupt the power to a circuit due to: Fault or

overload condition.(The current flow exceeds safe level).

Fuse :

 Consists of a piece of copper or tin-lead alloy wire, which will

melt when carrying a predetermined current.

 The element with contacts, carrier and base is called a fuse.

 Fuse is placed in series with the circuit to be protected, and

automatically breaks the circuit when over loaded.

45
 Cont.
 The time for blowing out of a fuse depends on the magnitude of excess
current. i.e. the larger the fault current the more rapidly the fuse blows.

 Three terms are used in connection with fuses.

o Current rating: this is the maximum current that a fuse will carry

indefinitely without undue deterioration of the fuse element.

o Fusing current: this is the minimum current that will ‘blow’ the fuse.

o Fusing Factor: this is the ratio of minimum fusing current to the

current rating

Fusing Factor =

46
 Cont.

Fuse holder

Different types of fuses

47
  Circuit Breakers/CB/

• A CB is a device designed to open and close a circuit by non- automatic

means and to open the circuit automatically on a predetermined over-

current without injury to itself when properly applied within its rating.

• So a circuit breaker is a combination device composed of a manual

switch and an over current device.

• A circuit breaker has several advantages over any type of fuse

 In the event of fault or overload all the poles are simultaneously

disconnected from the supply

 the circuit can be closed again quickly onto the fault safely
48
 Cont.
• Circuit breakers are rated in amperes just as fuses are rated.

• Like fuses, breakers are tested to carry 110% of their rated loads indefinitely

without tripping.

• Most breakers will carry 150% of their rated load for perhaps a minute, 200%

for about 20 sec. and 300% for about 5 sec, long enough to carry the heavy

current required to start most motors.

• Fuse has higher risk of causing a fire than circuit breaker due to

 loosely screw

 contact corroding

 wrong size 49
 Cont.
• Standard ratings: both fuse and
circuit breakers are available in
standard ratings of 6, 10, 16, 20,
25, 35, 50, 63, 80, 100, 125, 160,
224, 250, 300, and large sizes.

50
  Distribution Board
• A distribution board is an assemblage of parts, including one or more

fuses or circuit breakers, arranged for the distribution of electrical energy

to final circuits or to other sub- distribution boards.

• It consists of a case inside which is a frame holding a number of fuses

(CBs) carriers behind the frame or something alongside or above it, is a

bus-bar to which the incoming sub-main is connected.

 From the bus-bar there is connection provided to one side of each fuse

way (CB).

 The installer to the outgoing terminal of the fuse ways then connects

each final sub-circuit 51

 Cont.

• The standard distribution boards usually have 4, 6, 8, 12, 18 or 24 fuse

(CB) ways both single phase and three phases are available. It is not
necessary to utilize all the available fuse ways on a board, and in fact it
is very desirable to leave several spare ways on each board for future
extension.
• In general distribution includes

 fuses
 circuit breakers
 main switches
 frame
 bus-bar 52
Cont.

53
Cont.

54
Cont.

55
 2.3. Electrical regulations, standards and symbols

 Most countries have national regulations and/or standard governing

the rules to be strictly observed in the design and realization of
electrical installations for residential and similar premises.
 Electrical installations shall comply with more than one set of
regulations, issued by National Authorities or by recognized private
bodies. It is essential to take into account these local constraints
before starting the design.
 Regulations and standards are two different things: Regulations
are the law and must be complied with; Standards on the
other hand are advisory .
56
 2.3.1.Electrical Installations Regulation
• The study of a proposed electrical installation requires an adequate

understanding of all governing rules and regulations.

• The Electrical installation regulation objectives are designed to protect

persons, livestock's and properties from fire shock burns and injuries

from mechanically moving parts which is actuated by electricity.

• The regulations which govern the installation work can be divided

into two categories (Statutory and Non-Statutory).

a. Statutory:-is a written law( as compared to oral or customary law). It is

originated from National state legislation and they don't tell as detail.

57
 Cont.
b. Non-Statutory:- based on the sources of law it’s authority rests
not on regulation but rather on tradition, custom, experience, etc.

 Our country wiring regulation is adopted from IEE (International

Electrical Engineering) Regulations harmonization with the
safety and health regulations.

 IEE wiring Regulations is based upon European Committee for

Electro technical Standardization (ECES) of harmonized
documents of formed from International Electro technical
Commission (IEC) standards.

58
 Cont.
• In general IEE regulations have the following parts

i. Scope, objective and fundamental requirements

ii. Definitions
iii. Assessments of general characteristics
iv. Protection for safety
v. Selection and erection of equipment's
vi. Special installation and location
vii.Inspection and testing
59
 2.3.2. Standards

 A standard is a document specifying nationally or

internationally agreed properties for manufactured

goods and equipment.

 There are three types of standards that are important to us:

British standards (BS),

European Harmonized standards (EN or BS EN),

International Electrical Commission standards (IEC)

60
 Cont.
 An international standard such as the IEC 60364 “electrical
installation in Buildings” specifies extensively the rules to
comply with to ensure safety and predicted operation
characteristics for all types of electrical installations.

 IEC 60364 has been established by engineering experts of all

countries in the world comparing their experience at an
international level. Currently, the safety principles of IEC 60364
series, IEC 61140, 60479 series and IEC 61201 are the
fundamentals of most electrical standards in the world.

61
 Cont.
EBCS-10 code standard for the Electrical installation of Buildings is part of

the Building Code of Ethiopia. This Code Standard for the Electrical

installation of Building is mainly adopted from IEE Regulations for

electrical installations and Canadian electrical code, part 1, to suit the

Ethiopian Conditions.

The code embraces several aspects of electrical installation work and sets

standards and provisions for safe utilization of electricity.

The major benefits to be gained in applying these standards are:

 To harmonize professional practice and

 T0 ensure an appropriate levels of safety, health and economy with due

consideration of the objective conditions and needs of the country. 62

 Cont.
Standard cable colors for flexible cable(Extension cords power line
cords and lighting cords) for different country are as shown in table

Region/country Phase color Neutral Color Protective /ground

EU, Australia Brown Blue Green/yellow

S.Africa (IEC)

Brazil Yellow/ red Blue Green

US/Canada Black/brass White/ Silver Green

63
 Cont.
• Standard cable colors for fixed cable (in, on or behind the wall
wiring cables) are as follow in table below.

Country Phases cable color Neutral Cable color Protective/Ground

EU,IEC, UK Brown, black, grey Blue Green/yellow

from march 31-
2004, Africa

UK before march Yellow, red, blue Blue Green/ yellow

31-2004

Brazil Yellow, red, black, Blue Green

white

USA Red Black Green/yellow

India red, blue, yellow Black Green

64
 Cont.
• For Ethiopia building code standard the wiring cable standard is
shown in table below.
FUNCTION COLOR

Earthing /protective line Green/yellow

Live of ac single-phase circuit Red or yellow or blue

Neutral of ac single-phase or three-phase Black
circuit

Phase R of three-phase ac circuit Red

Phase S of three-phase ac circuit Yellow

Phase T of three-phase a.c. circuit Blue

65
2.3.3. Electrical Installation Symbols

66
Cont.

67
Cont.

68
Cont.

69
Cont.

70
Cont.

71
Cont.

72
Cont.

73
Cont.

74
Cont.

75
 Cont…

2/25/22 76
77