CHAPTER THREE

ELECTRICAL INSTALLATION

MATERIALS AND ACCESSORIES

3.1. Electrical Installation Materials

3.2. Electrical regulations, standards and symbols

1
3.1. Electrical Installation Materials
• 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
3.1.1. 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.

 Cable: several wires stranded together.

3
 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,

Safely and

With less voltage drop

4
Parts of a Cable
A cable consists of three parts:

 The conductor or (the core):- the metal wire or strand of wires carrying 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.

5
a. Conductor materials used in cable

• Conductor (of cable) is a part of a cable which has the specific function for carrying

current.

• It 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.

6
 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 has resistivity of 1.786 x 10-8

Ωm at 200c temperature.

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

for long distance power distribution.

7
 Cont.

• The electrical conductivity of aluminum is about 60% of that of copper and it has

the electrical resistivity of pure aluminum at 200c is 2.6 x 10-8 Ωm.

• 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.

8
 Cont.
• The size of conductors shall be such that

 the voltage drop b/n 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 & insulated copper conductors for power & 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

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b. Insulating Materials

 Insulation is 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.

 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.

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 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.

11
 Cont.

The various types of insulating materials used are :-

1.Rubber

2. PVC (Polyvinyl chloride)

3.Vulcanized India Rubber(VIR)

4.Impregnated Paper

12
 Cont.
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,

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 Cont.
2. PVC (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.

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 Cont...
3. Vulcanized India Rubber (VIR): 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 & becomes brittle with age.

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

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 Cont.
4. Impregnated Paper:- is quite cheap, has low capacitance, high dielectric strength

(30KV/mm), and high insulation resistivity (10Mohm-cm).

• Its main advantage is that a cable of given size can be worked out at a higher current

density than a VIR cable.

• The insulation on its own would be too fragile to be used unprotected, and a lead

sheath is applied over the insulation.

• It is used for conveying large power in transmission and distribution and

particularly for distribution at low voltage in congested areas.

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17
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 damage.

• It 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.

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 Types of Cables used in internal wiring

• The wires used for internal wiring of buildings may be divided into 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).

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 Cont.

• According to voltage grading the cables may be divided into 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 cord cables

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 Cont.

1. Vulcanized Indian Rubber (VIR) cables:- are available in 250/440volt as well as

650/1100 volt grades and are used for general conduit wiring.

2. 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.

21
 Cont.

3. Lead sheathed cables: it is available in 250/440 volt grade and used for internal

wiring where climatic condition has moisture.

• It is a vulcanized rubber insulated conductor covered with continuous sheath of lead .

• The sheath provides very good protection against the absorption of moisture and

sufficient protection against mechanical damage and can be used without casing or

conduit system.

• Available as single core, flat twin core, flat three core & flat twin core with ECC.

22
 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.

23
 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.

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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

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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 effect.

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

4. Cost : Cost is also a important factor.

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Insulating Materials General Properties

The properties can be classified as

 Electrical properties.

 Thermal properties.

 Chemical properties.

 Physical/Mechanical properties

Reading Assignment

27
 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

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3.1.2. 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.

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 Cont.
• 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.

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i. Light gauge steel conduit
• This type of conduit is used with special grip fittings.

• Available with external diameter of 12mm, 16mm, 19mm, 25mm, 31mm, 38mm, & 50mm.

• In general, light gauge is the cheapest & quickest of conduit installations but should be used

at road crossing & where the location is dry & there is little likelihood of mechanical damage.

• It is available up to 6 meters.

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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.

• They are available in approximately 20meter lengths & are threaded at the two ends.

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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 & are easily bent no elbow is required.

 Commonly used for protecting the final connections of motors.

 The flexible conduit is costlier than the rigid conduit. 33

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.

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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

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 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 & this expansion must be allowed

for.

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

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Conduit wiring
• There are three types of 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.

37
 Cont.

b. Surface conduit wiring: The conduit is placed on the surface of the wall with the help of saddle.

• 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.

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Conduit Accessories and Fittings
 Conduit Couplers: are used to join two lengths of conduit. Screwed conduits are always

threaded at both ends on the outer side.

 Conduit Bends, Elbows & Tees: In general conduit fittings include bends, elbows & 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.

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• Conduit boxes:
Cont.

 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. The conduit
Outlet box/Terminal box

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.

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Junction box
 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.

 it prevents the insulation of cables from getting damaged.

 it helps in securing the rigid conduit with conduit box

41
 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 & electrically continuous.

• They are formed out of thin steel metal sheet with

outer side octal & inner hole threaded as standard pipe.

Inspection elbow (Screwed): the inspection elbow is

used where right angle run of conduit bends is required

regularly
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3.1.3.Switches

 Are used to control lighting circuits.

 Most are rated at 5/6A, but ratings at 10/15A 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 control of a number of different circuits from one position, switches are

contained within the same unit: two-gang, six-gang, etc.

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 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.

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3.1.4. 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.S).

45
 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.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 insulated type of Bakelite or the brass type with

porcelain interior.

Bakelite type brass type 46

3.1.5 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 into the contact tubes.

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3.1.6.Fuse and Circuit Breakers

 Designed to interrupt the power to a circuit due to: Fault or overload condition.

(when 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 it is overloaded.

48
 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

𝑚𝑖𝑛𝑖𝑚𝑢𝑚 𝑓𝑢𝑠𝑖𝑛𝑔 𝑐𝑢𝑟𝑟𝑒𝑛𝑡

Fusing Factor = ≥1
𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑟𝑎𝑡𝑖𝑛𝑔
49
 Cont.

Fuse holder

Different types of fuses

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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 damage to

itself when properly applied within its rating.

• A CB is a combination device composed of a manual switch & an overcurrent

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
51
 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
52
 Cont.

• Standard ratings: both fuse and circuit breakers are available in standard ratings

of 6, 10, 16, 20, 25, 32, 40, 50, 63, 80, 100, 125, 160, 225, 250, 300, and large

sizes.

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3.1.7. Distribution Board (DB)

• A DB is an assemble of parts, including one or more fuses or CBs, 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
54
 Cont.

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

both single phase & 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 board includes

 fuses/circuit breakers

 main switches

 frame

 bus-bar 55
Cont.

56
Cont.

57
Cont.

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3.2. Electrical Regulations, Standards and Symbols

 Most countries have national regulations and/or standards 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 .

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3.2.1.Electrical Installation Regulations

• 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 damages 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.

60
 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 formed from International

Electro technical Commission (IEC) standards.

61
 Cont.
• In general IEE regulations have the following contents

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

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3.2.2. 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)

63
 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.

64
 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

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

the objective conditions and needs of the country.

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 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 S. Brown Blue Green/yellow

Africa (IEC)

Brazil Yellow/ red Blue Green

US/Canada Black/brass White/ Silver Green

66
 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 67

 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 circuit Black

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

68
3.2.3. Electrical Installation Symbols

69
Cont.

70
Cont.

71
Cont.

72
Cont.

73
Cont.

74
Cont.

75
Cont.

76
Cont.

77
Cont.

78
 Cont…

December 17, 2024 79

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