EEC 129 Theory

September 19, 2017 | Author: VietHungCao | Category: Cable, Insulator (Electricity), Electrical Conductor, Electric Shock, Electrical Wiring
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YEAR I- SEMESTER II THEORY Version 1: December 2008


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 1.1



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


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


1. Electrical Safety


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


1. Electrical Safety





1 mA or less

Causes no sensation - not felt.

Safe Current Values

Sensation of shock, not painful; 1 mA to 8 mA

Individual can let go at will since muscular control is not lost. Painful shock; individual can let go at

8 mA to 15 mA

will since muscular control is not lost. Painful shock; control of adjacent

15 mA to 20 mA

muscles lost; victim can not let go. Ventricular fibrillation - a heart

Unsafe Current Values

Condition that can result in death - is 50 mA to 100 mA

possible. Ventricular fibrillation occurs.

100 mA to 200 mA

Severe burns, severe muscular Contractions - so severe that chest

200 mA and over

muscles clamp the heart and stop it for the duration of the shock. (This prevents ventricular fibrillation).

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


1. Electrical Safety


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








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.


1. Electrical Safety


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)


1. Electrical Safety


Figure 1-2 Use the safety model to recognize, evaluate and control workplace

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.

Figure 1-3

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


1. Electrical Safety


 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

Figure 1-4

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


1. Electrical Safety


 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 Figure1-5 : Keeping the ladder still is a must


1. Electrical Safety


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


1. Electrical Safety 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). 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.


1. Electrical Safety


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

Figure 2

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


1. Electrical Safety


(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

Figure 1

casualty's forehead. Allow to 10 seconds to determine if there is a pulse (See Figure).


1. Electrical Safety


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.


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.


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.


1. Electrical Safety


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

Figure 1

performing any electrical work.


1. Electrical Safety


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.

Figure 1

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.

Figure 1

Use insulated pliers when doing electrical work.

Keep pliers grips free of grease or oil, which could cause them to slip. 15

1. Electrical Safety


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

Figure 1

them to slip.


2. Electrical and Electronics Symbols 3.0



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.


2. Electrical and Electronics Symbols


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


2. Electrical and Electronics Symbols


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


2. Electrical and Electronics Symbols


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.


2. Electrical and Electronics Symbols


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 21

2. Electrical and Electronics Symbols


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


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


b) Aluminium Is available in many form, generally used in electrical applications. The table (4-1) shows different types of conductors.



















9 10



- Cable and wires. - Busbars and contactors. - Industrial applications. - Power Cables . - Industrial applications.

- Very good conductor. - Easily-worked metal. - Tough. - Cheaper than copper. - Low cost and weight. - Ease for fabrication.

- Heating elements. - Manufacture resistance. - Motor bruches. - Resistors. - Some types of contants. - Fine instrument wires. - Plating contact surface. - Plating contact surface. -Terminals. - Parts of electric fittings. - Plug pins.

- Hard element. - Resists corrosion. - Hard. - Low friction with other metals. - Best conductor. - Expensive. - Expensive. - Does not corrode. - Easily cast. - Easily tinned for soldering.

- Lamp filaments.

- Easily drawn.

- Switch gear compnents. - cheap. - Conduit and fittings. - Resistance grids - Special contacts. - Liquid at normal temperature. Mercury - Discharge lamps. - Vaporises readily. Table (4-1) : Shows adifferent types of electrical conductors. Zinc


3. Cables in Electrical Installation


4. 2 Conductor characteristics Conductors have three characteristics are: 1) Electrical. 2) Physical. 3) Chemical.

4.2.1 Electrical Characteristics a) Resistivity "Resistivity" is the resistance of a piece of the conductor with unit length and unit cross- sectional area . The resistivity is related by: R =


ρL A

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 ).

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:

ρ L R =

R =

A 1.78 × 10-8 × 1000 4 × 10

R = 4.45 Ω


L = 1000 m ρ = 1.78 × 10-8 Ω.m A = 4 mm2 = 4 × 10-6 m2

b) Conductivity "Conductivity" is the degree of ease by which an electric current passes through the material. 25

3. Cables in Electrical Installation


The Conductivity is related by: ρL 1A ρ : Conductivity (1/ Ω.m)

τR ==



ρ : resistivity (Ω.m ).

c) Temperature coefficient Change of temperature can affect the resistance of a conductor. 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 R2 = R1[ 1+ α (t2-t1)] 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.

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 26

3. Cables in Electrical Installation


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.


3. Cables in Electrical Installation


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






Mineral oil

Synthetic rubber







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

4.4 Insulator characteristics Insulator have two characteristics are: 1) Electrical. 2) Physical.


3. Cables in Electrical Installation


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


3. Cables in Electrical Installation


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 singlecore 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


a) Flexible cables ( flexible cord ) 1- P.V.C insulated single core wire. 2- Tow core or (twin ) cable.

Domestic and industrial work.

( two single isulated-stranded wire ). 3- Three core ( twisted ). b)Sheathed cables 1- P.V.C sheathed cables. 2- Tough rubber sheathed cables ( TRS ).

Domestic and industrial wiring.

3- Lead alloy P.V.C sheathed ( LAS ). 4- P.C.P ( polychloroprene sheathed cable ). Table (4-3) : Wires and cables used in domestic installations.


3. Cables in Electrical Installation


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.

a) P.V.C insulated single core wire

7- Electric-sign cables. 8- Equipment wires.

c) b) Circular flexible cable

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


3. Cables in Electrical Installation


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 ).


3. Cables in Electrical Installation

Nominal Crosssectional area of copper conductor (mm2) 0.75 1 1.5 2.5 4 6 10 16 25 35 50 70 95 120 150 185 240 300 400 500

Group 1 One or more Single-core cable in conduits Carrying capacity (A) 11 15 20 25 33 45 61 83 103 132 165 197 235 -

Group 2 Multicor e cables Rated fuse current (A) 6 10 16 20 25 35 50 63 80 100 125 160 200 -


Group 3 Singlecore cable in air Carrying capacity (A) 12 15 18 26 34 44 61 82 108 135 168 207 250 292 335 382 453 504 -

Rated fuse current (A) 6 10 10 20 25 35 50 63 80 100 125 160 200 250 250 315 400 400 -

Carrying capacity (A) 15 19 24 32 42 54 73 98 129 158 198 245 292 344 391 448 528 608 726 830

Rated fuse current (A) 10 10 20 35 35 50 63 80 100 125 160 200 250 315 315 400 400 500 603 630

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


4. Simple Lighting Circuits


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.


4. Simple Lighting Circuits


 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.


4. Simple Lighting Circuits 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


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.




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 labourhours 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.



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.



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.



………………………………. ELECTRICAL CO LTD

Materials Manuf cv


Unit price Mat cost

Labour unit

Labour hrs



Estimator……………… subject………. Date…… Table (5J) Price sheet


Est no/




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



allowances for transport for labours. - Insurance for workers and other insurance. - Some other allowances when the working conditions are abnormal.



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


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




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




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


Bedroom lights and lights for stairways and halls should be controlled with a twoway 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


Fig 5.7 lighting of a stairway


Fig 5.8 Outside lighting


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.

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