Chapter 2

Electrical Installation in Consumer premises

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 Introduction
 Electrical installation refers to the practice of electrical wiring and associated system used to convey
electric power to electrical loads in a consumer’s premises in a safe, reliable and efficient manner.

 The consumer can be a residential, a public, a commercial or an industrial entity.

I. Residential premises may be of villa, G+1 or more buildings as well as apartment storeys.

II. Public buildings include religion establishments such as churches, mosques, educational
establishments such as schools, colleges, universities, health care establishments, etc.

III. Commercial buildings include hotels, restaurants and cafes; office apartments, shopping
centers and displays, and supermarkets, etc.

IV. Industrial establishments include small to large scale manufacturing, production etc. facilities.

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 2.1.Regulations and Standards
 Electrical installation regulation: a set of rules that need to be followed as guidelines to ensure safety,

reliability, stability, energy efficiency during operation of the system.

 Electrical installations may need to comply with more than one set of regulations, issued by National Authorities

or by recognized private bodies.

 These regulations may be based on national standards derived from the IEC ( International Electrotechnical

Commission) 60364: Low-voltage electrical installations

 National Electrical Code (NEC)

 BRITISH STANDARD

 It is essential to take into account these local constraints before starting the design.
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Standards
 This Guide is based on relevant IEC standards, in particular IEC 60364.

 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.

 The Ethiopian Building Code Standards EBCS-10, prepared by the Ministry of Works and
Urban Development in 1995 is the formally compiled standard.

 Electric Installation Regulation compiled by the Ethiopian Electric Light and Power
Authority – EELPA (Ethiopian Electric Power Corporation - EEPCO) around 1969.
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 2.2 Electrical installation materials and accessories

1. Conductors

 A conductor is a material which offers a low resistance to current.

 It is used to produce electric wires and cables.

 The necessary requirements of a wire (and also cable) conductor are that it must

conduct electricity efficiently, mechanically strong and flexible, relatively cheap and safe.

 Typical materials used as conductors in electrical installation work include, Copper,

Aluminum
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 Cont.d

i) Copper

 Is the next best conductor after silver which is comparatively cheap and thus

commonly used as wire conductor or cable.

Electrical resistivity of pure copper at 200 C is 1.786 x 10-8 ohm-m (or 1.72

𝝻𝝮cm).

Copper is mechanically strong

It is highly resistive to corrosion, oxidation. 6

 Cont.d
ii) Aluminum

 Coming in to increasingly use for overhead transmission cables and

sometimes as bus bars although not good conductor as copper.

 But its light weight is an advantage.

 Aluminum has a resistivity of 2.6𝝻𝝮cm.

 It is frequently used in place of copper for bare electric cables used for long
distance power distribution.
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 Cont.d

iii) Brass

Often used for manufacturing of terminals, contact points and various

parts of fittings.

Gold, platinum, silver, mercury (best but expensive).

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 Cont.d
2. Insulators
 Are used to isolate electrically conducting parts of a circuit as well as humans.

 should have the following properties:

 high electric resistance,

capability to withstand high breaking voltages,

high temperature/heat resistance without deterioration,

non-inflammability; high mechanical flexibility;

 highly resistive to moisture, acids or alkalis.

 Typical insulating materials (in wires and cables) are: Rubber, Polyvinyl chloride,
Cross-linked polyethylene and etc. 9
 Cont.d
i) Rubber

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 Cont.d
ii) Polyvinyl chloride (PVC)

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 Cont.d

iii) Cross-linked polyethylene

It is used for insulation of high tension electrical cables.

XLPE has excellent dielectric properties, making it useful for medium

voltage (10 to 50 kV AC) and high voltage cables (up to 380 kV AC
voltage). 12
 Cont.d
3. Wire
 A wire conductor can be bare or insulated as well as stranded (for flexibility) or solid.

 Commercial cables with conductor wires of cross sectional area above 25mm 2 are generally
stranded.

 Its insulation should be such that it prevents leakage of current in unwanted direction and to
minimize risk of fire and shock.

Wires (solid and stranded conductors)

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 Cont.d
4 Cable
A cable is a length of two or more insulated/sheathed conductors (solid or stranded
and twisted together) each provided with its own insulation.

 Electric current and hence energy flows through the cable.

A cable comprises of three main components: the conductor and/or core, the
insulation or dielectric, and the amour and/or sheath protective cover.

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 Cont.d
Multi-stranded cables have the following advantages over single solid conductors.

More flexible

Have more surface area

Skin effect is better

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 Cont.d
The wires used for internal wiring of buildings divided in to different groups as follow;

 According to the type of conductor – copper or aluminum and solid or stranded.

 According to the number of cores, cables may be divided in to classes, [single core, twin core]

 According to voltage grading (voltage that the insulation can withstand) cables may be
divided in to (low-voltage or medium-voltage) :
 250/440 Volt cable

 650/1100 Volt cable

• According to type of insulation cables can be classified in to:

(Note: A cable usually derives its name from the type of insulation used to confine the wires. For
example PVC cable, multicore cable, tough-rubber sheath cable, steel armored cable, etc. )16
 Conduits, truncking and ducting
Conduits

Conduits are non-metallic or metallic pipes through which installation wires and
cables are drawn for mechanical as well as electrical protection.

Mostly, non-metallic conduits such as the PVC (soft or rigid) type are used

Conduit is made in both light gauge and heavy gauge of which heavy gauge is
much more frequently used.

In general, conduits can be classified as PVC conduit, light gauge steel-plain
(unscrewed) conduit, heavy gauge conduit and flexible conduit
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 Installation accessories and fittings
Switches
 Generally a switch is a device which is used to make and brake contacts in an electric circuit thereby
controlling the flow of power to a load.
 The switch conducting parts and screwed connecting terminals are made of good electrical conductors

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 Cont.d

Lamp Holders

 Lamp holders are designed for quick insertion, removal and replacement of

lamps and yet they must hold the lamp in firm and good electrical contact to

prevent overheating.

 May be fitted in a luminary.

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 Cont.d
Socket Outlets

Socket outlets are portions of the wiring system in which mobile

electrical appliances would get access to electric power

A socket outlet may comprise of two/three contact tubing terminals for

single phase ungrounded/ grounded or 3/4/5 tubes for three phase with
the phases only/phases + neutral/phases + neutral + earth(ground).

Socket out lets are rated by the capacity of current they can carry:10A,
16A, 25A, etc.
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 Protective Devices
It is impossible for an electric current to flow through a wire without heating the wire however
small the temperature may be.

Fire occurs when over current flows in a wire or a load and this current produces heat on the
wire and on the insulation enough to burn it.

Two common protective devices use fuse protection and automatic circuit breaking protection.

Both a fuse and a CB are connected in series with the live wire in ac circuits to be protected.

 In 3-phase 4 wire systems, since only three lines are live, fuses and circuit breakers are
inserted in all the three lines except the neutral.

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2.3.Electrical installation design of a consumer
The kWh/kVAR meter, usually owned by a power utility, establishes the boundary
between the utility and the consumer.

The overhead/underground cable conductor feeding power from the last pole of the
utility company to the consumer building where the conductors are supported by
insulated strains is called service drop.

Cable from the utilities operating company line to the energy meter at the consumer’s
intake point is called the service cable or line

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 Cont.d
Utility companies and building code standards describe service requirements,[EBCS-10 pp144].

Clearance from Building opening

 Service conductor installed as open conductor or multi-conductor cable without any overall
other jacket shall have a clearance of not less than 925 mm from windows, doors, porches,
fire escape, or similar locations.

 Service conductors shall not be installed beneath openings through which materials may be
moved.

 Overhead wire shall not be run such that they obstruct entrance to these buildings openings.

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 Cont.d
The service-entrance equipment is a system including at least three elements.

This is because it is essential that the consumer supply should be effectively

controlled and also that all switch gear should be accessible.

The main switch gear installation should consist of:

I. means of isolation the supply

II. means of protection against excess current due to overload or short circuit (plus
earth-leakage protection if required),

III. Means of measuring the energy.

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 Cont.d
A main switch containing a fuse for single phase (3 fuses for 3 phase) fulfills
these conditions as the switch isolates the supply while the fuse/s protect/s
the circuit against excess current due to over load, short circuit or a serious
earth fault.

An automatic circuit breaker (ACB) does the job of both the main switch and
fuses but at a higher price.

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 Cont.d

Figures 2.2: Typical service-entrance equipment for a residential or small commercial customer

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 Cont.d
Main and sub distribution boards (MDB and SDBs) are assemblages of parts,

including one or more fuse and/or circuit breakers on copper bus bars arranged

on rails/bridges for the distribution of electrical power to the final sub-circuits or to

other sub distribution boards.

A medium or high voltage supplied consumer usually uses three phase supply

without/with step down transformer.

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 Cont.d
Arrangement of installation components
Inside the consumer’s premises there are basically two ways of distributing
power i.e. MDB-to-SDB interconnection.

Figure 2.3: (a) Only from MDB to SDB, and (b) from MDB to SDB, and from SDB to
28 SDB
 Cont.d
Depending on the particular need in the installation design, the following are involved :
 Lighting installation & fitting
 General purpose socket outlet
 Power (and special purpose) socket outlet
 Trunking/feeder installations,
 Main switchgear feeders
 Sub-mains and distribution gears
 Earthing system,
 Lightening protection systems
 Substation cables
 Substation transformers
 Substation switchgear,
 Power factor correction apparatuses. 29
 Cont.d

Branch circuit

Is the last portion of the installation in which one or more parallel connected loads are supplied with electric
power as well as use one common isolating and protective devices.

However, each load in a branch circuit is controlled separately with its own control such as a switch or a
starter/contactor.

The following constitute a branch circuit:

 a high power socket outlet (such as for cooking range, stove or boiler),

 a motor supply circuit,

 a group of light points,

 a group of general purpose socket outlets,

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 a small group of light points plus small number of low power socket outlets, etc.
Thank You!
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