EEC 129 Theory

1

UNESCO-NIGERIA TECHNICAL &

VOCATIONAL EDUCATION

REVITALISATION PROJECT-PHASE II

L

N

YEAR I- SEMESTER II

THEORY

Version 1: December 2008

NATIONAL DIPLOMA IN

ELECTRICAL ENGINEERING TECHNOLOGY

ELECTRICAL BUILDING

INSTALLATION

COURSE CODE: EEC 129

Table of Contents

Week 1: Electrical Safety--------------------------------------1

Week 2: Electrical Safety----------------------------------------9

Week 3: Electrical and Electronics Symbols-----------------16

Week 4: Electrical and Electronics Symbols-----------------19

Week 5: Cables in Electrical installation---------------------22

Week 6: Cables in Electrical Installation---------------------24

Week7: Cables in Electrical Installation---------------------27

Week 8: Cables in Electrical Installation---------------------31

Week 9: Simple Lighting Circuits------------------------------33

Week 10: Cost Estimation in Planning-----------------------36

Week 11: Cost Estimation in Planning-----------------------39

Week 12: Electrical bill of Quantities-------------------------42

Week 13: Allocation Plan----------------------------------------45

Week 14: Allocation of Lighting and Power Points--------47

Week 15: Allocation of Lighting and Power point---------49

1. Electrical Safety WEEK 1

1

1.1 Introduction

Electricity can kill. Whenever you work with power tools or on electrical circuits,

there is a risk of electrical hazards, especially electrical chocks. Working with

electricity can be dangerous. Engineers, electricians, and other professionals work

with electricity directly, including working on overhead lines, cable harnesses, and

circuit assemblies. Others, such as office workers and salespeople, work with

electricity indirectly and may also be exposed to electrical hazards.

Many workers are unaware of the potential electrical hazards present in their work

environment, which makes them more vulnerable to the danger of electrocution.

What are the Hazards?

Contact with live parts causing shock and burns

Faults which could cause fire

Fire or explosion where electricity could be the source of ignition in a

flammable atmosphere

Electrical shock is caused by completing an electrical circuit by:

Touching a live wire and an electrical ground

Touching a live wire and another wire at a different voltage

The danger from electrical shock depends on:

The amount1 of current through the body

The duration of current through the body

The path of current through the body

1 Amount of current is the number of free electrons passing, and is measured by (Ampere)


2

Burns are the most common injury caused by electricity:

Electrical burns

Arc burns

Thermal contact burns

Electric shock can cause muscle spasms, weakness, shallow breathing, rapid

pulse, severe burns, unconsciousness, or death.

In a shock incident, the path that

electric current takes through the body

gets very hot.

Burns occur all along that path,

including the places on the skin where

the current enters and leaves the body.

It’s not only giant power lines that

can kill or injure you if you contact

them. You can also be killed by a

shock from an appliance or power cord

in your home. Electrical Shock


3

Table 1.1 Shows the dangerous of electricity according to the amount of current

Strange as it may seem, most fatal electrical shocks happen to people who

should know better. Here are some electro medical facts that should make you think

twice before taking chances.

It's not the voltage but the current that kills. People have been killed by 240

volts AC in the home and with as little as 24 volts DC. The real measure of a shock's

Effects Readings Condition

Causes no sensation - not felt. 1 mA or less

Safe Current

Values

Sensation of shock, not painful;

Individual can let go at will since

muscular control is not lost.

1 mA to 8 mA

Painful shock; individual can let go at

will since muscular control is not lost. 8 mA to 15 mA

Unsafe Current

Values

Painful shock; control of adjacent

muscles lost; victim can not let go.

Ventricular fibrillation - a heart

15 mA to 20 mA

Condition that can result in death - is

possible.

Ventricular fibrillation occurs.

50 mA to 100 mA

Severe burns, severe muscular 100 mA to 200 mA

Contractions - so severe that chest

muscles clamp the heart and stop it for

the duration of the shock. (This

prevents ventricular fibrillation).

200 mA and over

Table 1

Effects of different current ratings


4

intensity lies in the amount of current (in milliamperes) forced through the body.

Any electrical device used on a house wiring circuit can, under certain conditions,

transmit a fatal amount of current.

Currents between 100 and 200 milliamperes (0.1 ampere and 0.2 ampere) are

fatal. Anything in the neighborhood of 10 milliamperes (0.01) is capable of

producing painful to severe shock.

As the current rises, the shock becomes more severe. Below 20 milliamperes,

breathing becomes labored; it ceases completely even at values below 75

milliamperes. As the current approaches 100 milliamperes ventricular fibrillation

occurs. This is an uncoordinated twitching of the walls of the heart's ventricles.

Since you don't know how much current went through the body, it is necessary to

perform artificial respiration to try to get the person breathing again; or if the heart is

not beating, cardio pulmonary resuscitation (CPR) is necessary.

Prevention is the best medicine for electrical shock. Respect all voltages,

have a knowledge of the principles of electricity, and follow safe work procedures.

Do not take chances. All electricians should be encouraged to take a basic course in

CPR (cardiopulmonary resuscitation) so they can aid a coworker in emergency

situations.

Always make sure portable electric tools are in safe operating condition.

Make sure there is a third wire on the plug for grounding in case of shorts. The fault

current should flow through the third wire to ground instead of through the

operator's body to ground if electric power tools are grounded and if an insulation

breakdown occurs.


5

1.1 First Aid

Shock is a common occupational hazard associated with working with

electricity. A person who has stopped breathing is not necessarily dead but is in

immediate danger. Life is dependent on oxygen, which is breathed into the lungs

and then carried by the blood to every body cell. Since body cells cannot store

oxygen and since the blood can hold only a limited amount (and only for a short

time), death will surely result from continued lack of breathing.

There are three stages of the safety model that are to be kept in consideration

1) Recognizing the Hazards

In order to avoid or control the hazards, you must recognize the hazards around you

2) Evaluating the Hazards

Identify all possible hazards first

Evaluate the risk of injury from each hazard

3) Controlling the Hazards

Create a safe work environment

Use safe work practices

In order to control the hazards around you in the workplace,

You must know what could go wrong while performing the job

You have the knowledge, tools and experience to do the work safely.

(You, coworkers and equipments should be safe)


6

Figure 1-3

And to control the hazards we should do the following:

a) Plan for the work to be done and plan for safety

Don't work alone, work with a

company who is trained and

who know what to do in an

emergency as well as you

should be aware of the hazards

around you in the workplace.

Know how to shut off and de-energize circuits to avoid any possible

electrical hazards

Figure 1-2

Use the safety model to recognize, evaluate and control workplace


7

Figure 1-4

Make sure that the energy sources are looked out

Remove jewelry and metal objects from your fingers, hands and neck

Avoid falls from scaffolding or ladders

b) Avoid dangers like wet workplace

Do not work wet

Do not work in damp conditions

like working outdoors while it's

raining

c) Avoid overhead power lines when

performing tasks under overhead power lines

d)Use proper wiring and connectors

Do not overload circuits like using a drill machine with a grinder and a

soldering iron in one extension cord

Test your equipments and tools regularly

Check switches and insulations of your tools

Use correct connectors keeping into consideration the connectors

ratings, sizes and materials

e) Use the tools properly

Inspect tools before using

Protect your tools by storing them correctly and by using them

correctly

f)Wear correct safety protective equipment

Wear proper clothing, overall, gloves, helmet, safety shoes, …etc

Wear proper foot protection

Wear safety eye glasses

Follow directions


8

Figure1-5 : Keeping the ladder

still is a must

Read the manufacturer's directions of cleaning and maintenance

carefully to know how the job should be done in the right way and with

the proper tools or equipments.

1.2 Using ladders

Ladders and scaffolding are used mainly in performing works at higher

positions than the reach of human body, like lights, street lights and overhead power

lines that are not too high.

To prevent dangers or injuries when climbing a ladder, do the following:

Check the condition of the ladder

Position the ladder at a safe angle to prevent

slipping

Make sure that the floor is level

Use special locks when necessary

Be careful when placing the ladder on wet or

any slippery surfaces

Follow the manufacturer's recommendations

for proper and safe use


9

Figure1-6: Spot the wrong practice. Figure 1-7: Carelessness may hurt you

1.3 Summary of chapter one:

Now since we incurred the safety in this chapter, you can relate this to your

major. In different tasks of maintenance operations in plants, laboratories, …, etc,

you should keep in mind:

Do not perform what you do not know

Be aware of what you are doing

Use the proper inspected tools

Wear the safety equipment

Do not work alone (Why?)

Do not work in bad moods

Create a safe working environment

Avoid, as much as you can, electrical hazards

Follow the safe working procedures

Do not take chances

Check what you did after finishing to keep others safe

Clean the place you accomplished your task in


10

2.0 Artificial Respiration

Victims of electrical shocks, drowning, gas poisoning or choking have

difficulty in breathing and may stop breathing altogether. Artificial respiration could

save their lives. Since most people die within 6 minutes after they stop breathing,

artificial respiration should begin as soon as possible after the breathing difficulty is

noticed.

2.1 Methods of Artificial Respiration

The are three methods of artificial respiration:

1. Mouth-to-mouth/ Mouth-to-nose

2. Chest pressure arm lift (Silvester)

3. Back pressure arm lift (Holger-Nielsen)

The most practical method is the mouth-to-mouth/nose method.

Step 1: Evaluation

a) Check for responsiveness of the victim.

b) Call for help.

c) Position the unconscious casualty so that he is lying on his back and on a firm

surface. If the casualty is lying on his

chest (prone position), cautiously roll

the casualty as a unit so that his body

does not twist (which may further

complicate a neck, back or spinal injury

as shown in figure 1).

2.2.1 Follow the following steps for rolling the victim:

1. Straighten the casualty's legs. Take the casualty's arm that is nearest to you

and move it so that it is straight and above his head. Repeat procedure for the

other arm.

Figure 1


11

2. Kneel beside the casualty with your knees near his shoulders (leave space to

roll his body). Place one hand behind his head and neck for support. With

your other hand, grasp the casualty under his far arm (See Figure above).

3. Roll the casualty toward you using a steady and even pull. His head and neck

should stay in line with his back.

4. Return the casualty's arms to his side. Straighten his legs. Reposition yourself

so that you are now kneeling at the level of the casualty's shoulders.

However, if a neck injury is suspected, and the jaw thrust be used, kneel at

the casualty's head, looking toward his feet.

Step 2: Opening The Airway-Unconscious and Not Breathing Casually

1. If there is any foreign matter visible in

the victim's mouth, wipe it quickly with

your fingers or cloth wrapped around

your fingers. Tilt the Head back so the

chin is pointing upwards. The victim

should be flat on his back. Pull or push

the jaw into a jutting out position for

removal of obstruction of the airway by

moving the base of tongue away from

back of throat (See figure 2).

2. Open your mouth wide and place it

tightly over the victim’s mouth. At the

same time pinch the victim’s nostrils shut

or close with your cheek. Or close the

with your cheek. Or close the victim’s

mouth and place your mouth over the nose blown into victim’s mouth or nose

Figure 2


12

(air may be long through the victim’s teeth even the are clenched the first

blown should be determine whether or not abstraction exists.

3. Remove your mouth, turn your head to side and listen for the return rush of

the air that indicate air exchange. Repeat the blowing effort. For the adult

blow vigorously at a rate of about 12 breaths per minute. For a child, take

relatively shallow breaths appropriate for the child's size, at a rate of about 20

per minute.

4. If the victim is not breathing out the air that you blew in, recheck the head

and jaw position. If you still do no get air exchange, quickly turn the victim

on his side and hit him sharply between the shoulder blades several times in

hope of dislodging foreign matter. Again sweep you finger through the

victim's mouth to remove foreign matter. If you do not wish to come in direct

contact with person, you may hold a cloth over the victim's mouth or nose

and breath through it. Cloth does not greatly affect the exchange of air.

5. After giving two breaths which cause the chest to rise, attempt to locate a

pulse on the casualty. Feel for a pulse on the side of the casualty's neck

closest to you by placing the first two fingers (index and middle fingers) of

your hand on the groove beside the

casualty's Adam's apple (carotid pulse).

(Your thumb should not be used for pulse

taking because you may confuse your pulse

beat with that of the casualty.) Maintain the

airway by keeping your other hand on the

casualty's forehead. Allow to 10 seconds to

determine if there is a pulse (See Figure).

Figure 1


13

a. If a pulse is found and the casualty is breathing --STOP; allow the

casualty to breathe on his own. If possible, keep him warm and

comfortable.

b. If a pulse is found and the casualty is not breathing, continue rescue

breathing.

c. If a pulse is not found, begin chest compression.

i. Expose chest and find breast bone. Put the heal of one hand

on breast bone and other hand on top.

ii. Compress the chest 15 times.

d. lf a pulse is not found, seek medically trained personnel for help.

For infants and small children:

If there is any foreign matter visible in the victim's mouth, wipe it quickly

with your fingers or cloth wrapped around your fingers.

i. Place the child on his back and use the fingers of both hands to lift the lower

jaw from beneath and behind, so that it juts out.

ii. Place your mouth over the child mouth and nose, making a relatively leak

proof seal and breathe into the child, using shallow puffs of air. The breathing

rate should be about 20/minute.

If you meet resistance in your blowing efforts, recheck the position of the

jaw. If the air passages are still blocked, the child should be suspended

momentarily by the ankles, or inverted over the arm and given two or three

sharp pats between the shoulder blades, in the hope of dislodging obstructing

matter.

Stopped breathing due to Suffocation:

After the person starts breathing give few doses of Camphor Q directly in

mouth which provides instant relief.


14

1.2 Handling Hand Tools Safely

An estimated 8% of industrial accidents are caused by hand tolls. These accidents

are caused by using the wrong tool for the job, using the right tool incorrectly,

failing to wear personal protective equipment, or failing to follow safety guidelines.

Take a moment to review these safety tips for handling common hand tools.

Screwdrivers:

Always match the size and type of screwdriver blade to fit the screw.

Don’t hold the work piece against your body while using the screwdriver.

Don’t put your fingers near the blade of the screwdriver when tightening a

screw.

Don’t force a screwdriver by using a

hammer or pliers on it.

Don’t use a screwdriver as a hammer or as

a chisel.

Don’t use a screwdriver if your hands are

wet or oily.

Discard and replace your screwdriver if it

has a broken handle, bent blade, etc

Use an insulated screwdriver when

performing any electrical work.

Figure 1


15

Hammer:

Use the correct hammer for the type of

work to be done.

Have an unobstructed swing area when

using a hammer and watch for overhead

interference.

Don’t strike nails or other objects with the

‘’cheek’’ (side) of the hammer.

Don’t use a hammer as a wedge or a pry

bar, or for pulling large spikes.

Don’t use a hammer if your hands are oily

or greasy.

Pliers:

Don’t use pliers as a wrench or

hammer.

Don’t use pliers that are cracked,

broken, or ‘’sprung’’

Don’t attempt to force pliers by using a

hammer on them.

Use insulated pliers when doing

electrical work.

Keep pliers grips free of grease or oil, which could cause them to slip.

Figure 1

Figure 1


16

Cutter

Don’t use cutter as a wrench or hammer.

Don’t use cutter that are cracked, broken, or ‘’sprung’’

Use insulated cutter when doing electrical work.

Keep cutter grips free of grease or oil, which could cause

them to slip.

Figure 1

2. Electrical and Electronics Symbols WEEK 3

17

3.0 Symbology To read and interpret electrical Figure 1 Basic Transformer Symbols diagrams and schematics,

the reader must first be well versed in what the many symbols represent. This chapter discusses

the common symbols used to depict the many components in electrical systems. Once mastered,

this knowledge should enable the reader to successfully understand most electrical diagrams and

schematics.

The information that follows provides details on the basic symbols used to represent

components in electrical transmission, switching, control, and protection diagrams and

schematics.

Transformers

The basic symbols for the various types of transformers are shown in

Figure 1 (A). Figure 1 (B) shows how the basic symbol for the transformer is modified to

represent specific types and transformer applications. In addition to the transformer Figure 2

Transformer Polarity symbol itself, polarity marks are sometimes used to indicate current flow in

the circuit. This information can be used to determine the phase relationship (polarity) between

the input and output terminals of a transformer. The marks usually appear as dots on a

transformer symbol, as shown in Figure 2.


18

Figure 2.

On the primary side of the transformer the dot indicates current in; on the secondary side the dot

indicates current out. If at a given instant the current is flowing into the transformer at the dotted

end of the primary coil, it will be flowing out of the transformer at the dotted end of the

secondary coil. The current flow for a transformer using the dot symbology is illustrated in

Figure 2.

Switches

Figure 3 shows the most common types of switches and their symbols. The term "pole," as used

to describe the switches in Figure 3, refers to the number of points at which current can enter

a switch. Single pole and double pole switches are shown, but a switch may have as many poles

as it requires to perform its function. The term "throw" used in Figure 3 refers to the number

of circuits that each pole of a switch can complete or control.

Figure 3 Switches and Switch Symbols


19

Table 4 provides the common symbols that are used to denote automatic switches and explains

how the symbol indicates switch status or actuation.

Table 4 Switch and Switch Status Symbology


20

Fuses and Breakers

Figure 5 depicts basic fuse and circuit breaker symbols for single-phase applications. In addition

to the graphic symbol, most drawings will also provide the rating of the fuse next to the symbol.

The rating is usually in amps.

Figure 5 Fuse and Circuit Breaker Symbols

When fuses, breakers, or switches are used in three-phase systems, the three-phase symbol

combines the single-phase symbol in triplicate as shown in Figure 6. Also shown is the symbol

for a removable breaker, which is a standard breaker symbol placed between a set of chevrons.

The chevrons represent the point at which the breaker disconnects from the circuit when

removed.


21

Figure 6 Three-phase and Removable Breaker Symbols

Relays, Contacts, Connectors, Lines, Resistors,

and Miscellaneous Electrical Components

Figure 7 shows the common symbols for relays, contacts, connectors, lines, resistors, and other

miscellaneous electrical components.

Figure 7 Common Electrical Component Symbols

Large Components


22

The symbols in Figure 8 are used to identify the larger components that may be found in an

electrical diagram or schematic. The detail used for these symbols will vary when used in system

diagrams. Usually the amount of detail will reflect the relative importance of a component to

the particular diagram.

Figure 8 Large Common Electrical Components

3. Cables in Electrical installation WEEK5

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4.1 Conductors

A" conductor " mean a material which allow the free passage of an electric

current along it, with very little resistance.

The conductor can be classified according its state as:

4.1.1 Gas Conductors

Used for electric-discharge lamps : neon, mercury vapour, sodium vapour,

helium; the latter is used in the "glow" type starter used in fluorescent starting

circuits.

4.1.2 Liquid Conductors

Used as electrolytes, like sulphuric acid ( lead-acid cells ), copper sulphate

acid ( in simple cells ). When salts are introduced to water,the liquid is used as a

resistor.

4.1.3 Solid Conductors

Copper and aluminium are the most common materials used as conductors

in electrical work.

a) Copper

Is available as :

Wire.

Bar.

Rod.

Tube.

Strip.

Plate.

It used for cables in domestic and industrial installations. Also in the basic

of

Many alloys found in electrical work.

3. Cables in Electrical installation WEEK5

24

b) Aluminium

Is available in many form, generally used in electrical applications.

The table (4-1) shows different types of conductors.

No. Conductor Applications Properties

1 Copper - Cable and wires.

- Busbars and contactors.

- Industrial applications.

- Very good conductor.

- Easily-worked metal.

- Tough.

2 Aluminium - Power Cables .

- Industrial applications.

- Cheaper than copper.

- Low cost and weight.

- Ease for fabrication.

3 Nickel - Heating elements.

- Manufacture resistance.

- Hard element.

- Resists corrosion.

4 Carbon - Motor bruches.

- Resistors.

- Some types of contants.

- Hard.

- Low friction with other

metals.

5 Silver - Fine instrument wires.

- Plating contact surface.

- Best conductor.

- Expensive.

6 Gold - Plating contact surface. - Expensive.

- Does not corrode.

7 Brass

-Terminals.

- Parts of electric fittings.

- Plug pins.

- Easily cast.

- Easily tinned for

soldering.

8 Tungsten - Lamp filaments. - Easily drawn.

9 Zinc - Switch gear compnents.

- Conduit and fittings.

- Resistance grids

- cheap.

10 Mercury - Special contacts.

- Discharge lamps.

- Liquid at normal temperature.

- Vaporises readily.

Table (4-1) : Shows adifferent types of electrical conductors.

3. Cables in Electrical Installation WEEK6

25

4. 2 Conductor characteristics

Conductors have three characteristics are:

1) Electrical.

2) Physical.

3) Chemical.

4.2.1 Electrical Characteristics

a) Resistivity

The resistivity is related by:

Where R: the value of the conductor resistance in ohm (Ω).

L: the length of the conductor in meters (m).

A: the cross-section area of the conductor, in square meters (m²)

ρ : resistivity (Ω.m ).

b) Conductivity

"Conductivity" is the degree of ease by which an electric current

passes through the material.

ρ L

A

R =

Example 4-1

Calculate the resistance of 1000 m of copper conductor, cross-sectional

area is 4 mm2 and the resistivity is 1.78 × 10

-8 Ω.m ?

Solution:

R =

R =

R = 4.45 Ω

L = 1000 m

ρ = 1.78 × 10-8

Ω.m

A = 4 mm2

= 4 × 10-6

m2

ρ L

A

1.78 × 10-8

× 1000

4 × 10-6

"Resistivity" is the resistance of a piece of the conductor with unit

length and unit cross- sectional area .


26

The Conductivity is related by:

Where τ : Conductivity (1/ Ω.m)

ρ : resistivity (Ω.m ).

c) Temperature coefficient

If the temperature increase, the dimensions of the conductor increase, thus

increase their resistance.

The following formula gives the value of the resistance as a function of a

temperature

where R1 : the resistance of the conductor at first temperature.

R2: the resistance of the conductor at second temperature.

α : temperature coefficient.

t1 : the first temperature.

t2 : the second temperature.

ρ L

A

R =

1

ρ

τ =

Change of temperature can affect the resistance of a conductor.

Example 4-2

The resitance of conductor is 20 Ω at temerature 30oC ,calculate the

resistance at 60 oC? assume α = 0.00396

Solution:

R2 = R1[ 1+ α (t2-t1) ]

R2 = 20 [ 1+ 0.00396 (60-30)]

R2 = 22.376 Ω

R2 = R1[ 1+ α (t2-t1)]


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4.2.2 Physical Characteristics

A conductor is physically characterized by different factors such as:

- Mass - Volume. - Density

- Tensil strength - Flammability - Elasticity

- Hardness. - Fusion point. - Toughness

4.2.3 Chemical Characteristics

The choice of a metal for being used as aconductor depends also on the

knowledge of its reaction with acids, bases and salts. Most of the metals are

attacked by acids, so we should be aware not mix or put acids on conductors.


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4.3 Insulators

"Insulator" is a material which does not allow the free passage of an

electric current.

Insulators are used to surround the conductor with a material that prevents

the direct touch of live conductor and to provide a protection from outer

damages.

Types of insulators

Table (4-2) shows different types of insulators.

Plastic materials Organic materials Mineral materials Liquid materials

Bekalite

Formica

Polyester

Synthetic rubber

PVC.(poly-vinyl-

chloride)

Cotton

Rubber

Paper

Wood

Mica

Amiate

Glass

Porcelain

Mineral oil

SF6

Table (4-2): Different types of insulators.

4.4 Insulator characteristics

Insulator have two characteristics are:

1) Electrical.

2) Physical.


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4.4.1 Electrical characteristics

The electrical state of an insulator is characterized mainly by:

- Dielectric strength.

- Breakdown voltage or current.

4.4.2 Physical characteristics

- Variation in temperature.

- Humidity.

- Dust.

- Flammability


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4.5 Wires and cables

4.5.1 Introduction

Wire and cables are used to conduct electric power from the generated

point to the point where it is used. Copper is the material used as conductor in

practically all casesCables consists of conductors, insulators and sometimes

mechanical protectors.The conductor is generally in the form of either a single-

core or two-core or three-core or multicore.

4.5.2 Types of wires and cables

The range of types of cables used in electrical work is very wide : from

heavy lead-sheathed and armoured paper-insulated cables to the domestic

flexible cable. Some examples of different cables are shown in figure (4-1).

The practical electrician will meet two common types of cables used in his

work. This types shown in the following table (4-3).

Cables Applications

a) Flexible cables ( flexible cord )

1- P.V.C insulated single core wire.

2- Tow core or (twin ) cable.

( two single isulated-stranded wire ).

3- Three core ( twisted ).

Domestic and industrial work.

b)Sheathed cables

1- P.V.C sheathed cables.

2- Tough rubber sheathed cables ( TRS ).

3- Lead alloy P.V.C sheathed ( LAS ).

4- P.C.P ( polychloroprene sheathed cable ).

Domestic and industrial wiring.

Table (4-3) : Wires and cables used in domestic installations.


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The following groups of cables are to be found in electrical field:

1- Power cables.

2- Mining cables.

3- Overhead cables.

4- Communications cables.

5- Appliances-wiring cables.

6- Heating cables.

7- Electric-sign cables.

8- Equipment wires.

Figure ( 4-1): Examples of different cable.

c)

a) P.V.C insulated single core wire

b) Circular flexible cable


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4-6 Cable Size

The cable size is classified according to current rating , where The rating

is defined as:

"cable rating" is the amount of current it can be allowed to carry continuously

without eteriorations.

The basic factor to be considerd when selecting the size of a cable is the

current of the circuit.

Many factors govern the rating of cable :

Conductor cross-sectional area.

Type of insulations.

Ambient temperature.

Type of protection.

Grouping.

Disposition.

Type of sheath.

Also, the current rating of a final subcuirect depends upon the actual

connected load. The cable selected to supply this load must be able to withstand

at least the rating current absorbed by the load without undue heating. This rating

current is obtained by calculation depending on the nature of the circuit, the

power absorbed by the load and the supply voltage. The current is sometimes

called the design current, and used to select the size of cable.

For ambient temperature up to 30oC, the permissible current carrying capacity

and the corrdination of line protection fuses are given in table (4-4 ).


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Table (4-4) : Conductors size and current carrying capacity

Nominal

Cross-

sectional

area of

copper

conductor

(mm2)

Group 1

One or more

Single-core

cable

in conduits

Group 2

Multicor

e

cables

Group 3

Single-

core

cable in

air

Carrying

capacity (A)

Rated

fuse

current

(A)

Carrying

capacity

(A)

Rated

fuse

current

(A)

Carrying

capacity

(A)

Rated

fuse

current

(A)

0.75

1

1.5

2.5

4

6

10

16

25

35

50

70

95

120

150

185

240

300

400

500

-

11

15

20

25

33

45

61

83

103

132

165

197

235

-

-

-

-

-

-

-

6

10

16

20

25

35

50

63

80

100

125

160

200

-

-

-

-

-

-

12

15

18

26

34

44

61

82

108

135

168

207

250

292

335

382

453

504

-

-

6

10

10

20

25

35

50

63

80

100

125

160

200

250

250

315

400

400

-

-

15

19

24

32

42

54

73

98

129

158

198

245

292

344

391

448

528

608

726

830

10

10

20

35

35

50

63

80

100

125

160

200

250

315

315

400

400

500

603

630

4. Simple Lighting Circuits WEEK8

34

4.1 Introduction

A lighting circuit is a combination of cables, conduits,protection devices,

control devices and equipment allowing the user to benefit from electric power.

There are many methods in which these elements can be connected.

The main devices encounted in domestic installation, other than protection

devices ( circuit breakers, relays, contactors, etc……. ) are :

Switches.

Ceiling roses.

Conduits and boxes.

Wires and cables.

4.2 Switches

Switch is a mechanical device for making and breaking electric current, non

automayically, a circuit carrying a current not greatly in excess of the rated

normal current of the switch. A switch is used for controlling a circuit or part of

A circuit.

4.2.1 Types of Switches

Single-pole switch

Usually called one way switch, controls the live pole of a supply, also these

switches provids ON and OFF control of a circuit from one position only. The

usual application to control the lighting circuits.


35

Double-pole switch

Control two poles, use of double-pole switch means that a two-wire circuit

can be completely isolated from the supply.

Figure (4-5) shows single & double pole switches. The usual application is for

the main control of sub-circuit and for the local control of cookers, water-heater

and other fixed current-using apparatus.

Figure (4- 5 ) : single pole switch

The following types of switches are to be found in electrical field :

Two-way switch.

Intermediate switch.

Two-gang switch.

Push Button switch.

Dimmer switch.

Night-light switch.

Pilot light switch.

Card operated ceiling switch.

Tumbler switch.

Rocker switch.


36

4.2.2 Rating

Switch rating is the maximum current and voltage at which it should be

operate. In domestic installations, the rating of switches as follows :

Lighting circuits 5A or 6A

Water heater 15A or 20 A

AC circuit 25A or 45A

4.2.3 Regulations

Some of Bahrain regulations are :

All switches must be fixed in P.V.C or a metal boxes.

The minimum height of fixed a light switch is 1.37m above floor level.

No switches can be situated in bathrooms.

The minimum cross-sectional area of conductors used in lighting circuit is

1.5mm².

An earthing terminal, connected to the protective conductor of the final

circuit, must be provided at each metal switch box.

COST ESTIMATION IN PLANNING WEEK

10

5.6 Cost Estimation

5.6.1 Important of cost estimation planning.

Having considered the technical aspects of contracting, that is, how to technically

carry out a particular installation, we now have to consider the business side. It is

quite clear that without being able to estimate the cost of a particular job, or being in

a position to give prospective clients a price for carrying out work, a contractor may

never have the opportunity to use this knowledge.

We cannot afford to quote too low a price, as this would involve the business in a

loss, yet i f the price is too high against that of the competitors, the work will go

elsewhere, and this happens two or three times, the client may refrain from inviting

further tenders.

5.6.2 Measurements

Estimating involves taking into account how the fob is to be carried out. This will be

generally stated in the specification or brief, taking into consideration site

conditions, and the construction of the building, measuring the quantity of materials

required, if no bill of quantity is given and on the basis of this, costing the materials

and labour required to carry out the work involved, making due allowance in

measurements for the fact that runs are not always straight, for switchdrops, wastage,

etc. Estimating the cost of materials is relatively simple, as long as careful

measurements are made; the quantity is multiplied by the net trade cost price of the

material, and listed.

Estimating the labour involved and costing it, is far more difficult, and even

nowadays experienced estimators do not always agree on the number of labour-

hours required for identical'work. Yet every installation is in fact made up of a

large number of small jobs. the fixing of a fuse-board, lying of conduit, wiring of

conduit fittings, etc. No matter how large the installation, it can always be divided up

into smaller divisions, and finally split up into individual small jobs.

The time taken for each individual job in repetion work, in. let us say, a factory

production unit, can be fairly closely established by time-and-motion study as

working conditions are fairly constant. In the case of contracting however where site

and working conditions vary so very much from contract to contract, and where the

wiremen may be fixing conduit one day and fuse-boards the next, this is far more

difficult.


10

Nevertheless it is possible to establish an average time factor for certain operations,

and these are listed in tables. It is not claimed that these tables are exhaustive or

precise, but the labour-hours stated are an average time taken per pair of men for

laying, let us say, 100ft of conduit and fixing conduit accessories under various

conditions, and sufficient information is given in the tables to cover most of the

work encountered

in normal wiring of buildings and cabling.

When estimating the time allowed for each operation this must be consistent in the

same way as the price for materials, and must not change with the mood of estimator

from one estimate to another.

5.6.3. Estimating the materials for a house

For most installations in buildings, the best way to sub-divide the installation is to

adopt a system such as the following:

1. Main switchgear

2. Sub-feeders

3. Sub-distribution boards

4. Lighting installation

5. Lighting fittings

6. Socket-out let installation

7. Other power circuits (machines)

8. Special rooms

9. Boiler house installation

10.Telephone installation

11.Internal telephone and call systems

12.Fire-alann system

13.Emergency lighting

(a). Emergency lighting unit

(b). Lighting installation.


10

14. Earthing and testing

and so on, and to deal with each item separately. This makes estimating easier,

gives a better overall picture, and ensure that nothing is forgotten. In many cases it

is advantageous to start the estimate with the lighting installation, as this enables

the estimator to familiarize himself with the extent of the building and its

constructions before tackling the more

difficult parts.

Estimates should be made in an estimate book or special pricing sheets semi-bound

so that they can be removed when the estimate is completed and filed on a separate

estimate file. Price sheets should be laid out as

shown in Table. (5-1 of men. rather than priced immediately, as labour rates

change, whereas the time taken for given operations is fairly stable.

Week 11

Cost Estimation Continued

Step 1:

Draw the execution plan of the circuit.

Step 2:

Layout the route of the conduits and the location of the boxes on the board.

Step 3:

Cut the conduit according to the sizes given on the layout diagram.

Step 4:

Make the required 90° bends as shown on the layout diagram. See Fig. (1.3 a, b), for bending springs and methods of bending.

Step 5:

Secure the conduit ends to the boxes, use adopters where necessary.

Step 6:

Secure the conduits to the board by saddles.

19 Questions:

1. How are switches, lamps and socket-outlets located in an

installation?

2. Define in general terms a branch circuit and state the rules of the determination of the branch circuit limit.

3. Show by drawings the difference between a main panel board and an auxiliary board. ..

4. Show by means of drawings a single-phase distribution sequence in an apartment.

5. Why cost estimation planning is important?

6. What are the factors involving estimating measurements?

7. Describe the procedure mostly used when estimating the materials

for a house.

8. How final cost for an installation is made up? Fig.(5.9) Shows a 13A socket outlet ring-circuit layout in a typical house.

Fig.(5.9) A 13A socket outlet fing-circnit layout in a typical house,

Fig. (5.10) shows the distribution of socket outlets on a first floor plan of

four-bedroom house.

ELETRICAL BILL OF QUATITIES WEEK

12

………………………………. ELECTRICAL CO LTD

PRICE SHEET

Estimator……………… client…………. Est no/ sheet…………

subject………. Date……

Table (5J) Price sheet

Materials Manuf cv Quaty Unit price Mat cost Labour

unit

Labour

hrs

remarks

Total


12

5.6.4 Final Costing

From the price sheets the cost of materials and labour has been established, but

this price must now be modified to take into account all the other expenses, and

work that is involved in carrying out a satisfactory installation.

At the beginning of every year management must decide what turnover they are

looking for. This may be based on the previous year's turnover or indeed if a newly

established company, a minimum turnover must be aimed for, in order to cover

costs.

The number of engineers, estimators, and other employed at Head Office must bear

some relation to turnover, and these salaried staff, together with office rents and

other expenses, storage, ...etc. form a fixed expenditure on overheads, irrespective

of turnover which must be covered by the contract price.

Let us assume that the total turnover target is BD. 80000 and the fixed overheads

are BD. 5000 per annum. Then, as a percentage the overheads are 6.25 percent and

the overall contract price must be increased by this percentage to cover Ac

overheads.

Moreover, each contract requires:

- Site working tools.

- Transport, even when the materials are purchased locally, also, transport or


12

allowances for transport for labours.

- Insurance for workers and other insurance.

- Some other allowances when the working conditions are abnormal.

ALLOCATION PLAN WEEK 13

INTRODUCTION

A technician should learn to read without errors in plans or schemes given to him by

an architect or a contractor for the realization of an electrical installation , He might

also need to establish by himself a plan or a scheme of an installation before

executing it or to modify an already done plan or scheme

Different type of plans and schemes exist, According to the importance and the

complexity of an electrical installation, plan may play different role. This chapter

will discuss the knowledge of many elements, which joined together, contribute in

making it easier for a technician to read and execute an electrical installation. And

after considering the technical aspects, we are going to discuss how to estimate the

cost of a particular job, or in other words how the job is to be carried out.

Examination and full understanding of allocation plan.

Allocation plan determines and shows the detail of an observed object according to

the direction from which we are looking at it. Accordingly ,six different location

plan exist, see fig. 5.1

ALLOCATION PLAN WEEK 13

Fig 5.1 Location Plan

Top view: Looking at the object from above.

Front view: Looking at the right in front of us.

Side view: Right and left side view, looking at the object from the sides

Rear view: Looking at the object from behind.

Bottom view: Looking at the object from under

Multi-view drawings are also called orthographic drawings A floor plan is a single,

view orthographic drawing of the outline and partitions of a building as you see

them if the building were cut horizontally about 12m above the floor line as shown

in fig 5.2

Fig 5.2 Sectioned Building

There are many types of floor plans, ranging from very simple sketches to

completely dimensional and detailed floor plan working drawings.

Designers substitute symbols for materials and fixtures.It is obviously more

convenient and time saving to

ALLOCATION OF LIGHTING AND

POWER POINTS

WEEK 14

Fig 5.3 shows the location plan of an apartment where the positions of the

door,windows and different sides of the apartment are indicated

Figure 5.3 Floor plan

Allocation of power points

After the basic floor plan is drawn,the designer should determine the exact position

of all appliances and lighting fixtures on the plan, as shown in fig 5.4

ALLOCATION OF LIGHTING AND

POWER POINTS

WEEK 14

Fig 5.4 Allocation of power point

The exact position of the switches and outlets to accommodate these appliances and

fixtures should be determined Next, the electrical symbols representing the

switches, outlets, and electrical devices should be drawn on the floor plan. A dotted

line is then drawn from each switch to the connecting fixture.

Lighting

The main sources of light in a room should be controlled by a wall switch ,type of

switch plate cover should be selected.

Fig 5.5 location of wall switch

ALLOCATION OF LIGHTING AND POWER

POINT

WEEK 15

Bedroom lights and lights for stairways and halls should be controlled with a two-

way switch as shown in fig 5.6 andfig 5.7 The outside lights must also be controlled

with two way switch from the garage and from the exit of the house as shown in fig

5.8.While basement lights should be controlled by a two way switch and a pilot light

in the house at the head of the basement stairs.

Fig 5.6 lighting of Bedroom


POINT

WEEK 15

Fig 5.7 lighting of a stairway


POINT

WEEK 15

Fig 5.8 Outside lighting


POINT

WEEK 15

SOCKET OUTLETS

Thereare several types of electrical outlets. The convenient outlet is the plug in .It is

available in single, double, triple, or strip outlets .The socket outlet is a connection

point of a cicuit for one special piece of equipment.

The basic rules to follow when planning the outlets location on a floor plan are,

1 . No socket outlets shall be mounted in any bathroom except for shower outlet that

is of low voltage

2.No socket outlet shall be mounted within two meters of any tap sink, bisin in any

kitchen or any place.

3.All socket outlets shall be mounted 30 cm above the floor.

4.Each room shall have at least one easy to reach outlet for the vacuum cleaner or

other appliances, which are often used.

Documents

EEC 129 Theory