Electrical Skills Lab Manual

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Shinas ollege of Technology

Engineering Department

E E l l e e c c t t r r i i c c a a l l s s k k i i l l

l l s s

L A B O R A T O R Y M A N U A L

Course Code: EEPW2241 AY 2015-2016 Semester: 2 ID No.: Name of the Student:

Section No. Level: Specialization:


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EEPW 2241: Electrical Skills Lab Manual Shinas College of Technology

Updated by Mr. Murali Krishna Boddu & Mr. Mahesh Aphale


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CONTENTS

Experiment

No.Name of the Experiment

Page

No.

Table of contents

Course objectives, outcomes

Course assessment scheme

Laboratory rules

General safety precautions and guidelines

in the ELECTRICAL SKILLS lab

Introduction

1 Electrical Supply

2 Measurement of the Earth Resistance

3 Preparation of Galvanized Steel Conduit

4 Wiring Lighting Circuit

5 Testing Wiring Circuits

6 Connection of Fluorescent Tube Light

7 Sodium Vapor Lamps

8Connection and Trouble Shooting of Fan

Circuit

9 Metal Halide Lamps


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COURSE OUTCOMES:

EEPW2241: ELECTRICAL SKILLS

Prerequisites: Engineering Workshop (EEPW 1240)

Goal: To provide the students with the concepts, techniques and applications of

electrical workshop

Objectives Outcomes

This course should enable the

student to:

1. Know the safety practices in

the workshop and production

areas.2. Understand the aspects of

electrical installation

techniques.

3. Understand how to assemble

steel conduit.

4. Understand how to wire

lighting and circuits.

5. Understand the concepts ofconstruction of DC and single-

phase AC motors.

6. Know different methods of

protections.

7. Understand how to control

circuits of single phase AC

motors.

Upon completion of the course, the student will be

able to:

1. Familiarize and apply the electricity safety

rules in Oman and in IEE regulation.

2. Describe the power distribution systems,Earthing arrangement, electrical bonding,

PME supplies and current protective

conductors.

3. Prepare for assembling steel conduit.

4. Wire lighting and power circuits.

5. Assemble and connect fluorescent and sodium

vapour lamps.

6. Test the wiring circuits like visual inspectiontest, continuity test and insulation resistance

test.

7. Define the fault diagnosis techniques in

electrical insulations.

8. Describe the construction of DC and single

phase AC motor.

9. Construct bell indictor circuits.

10. Apply different methods of circuit’sprotection.

11. Control the circuits of single-phase AC motors.


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Sources:

I. Text Books

1. “Electrical Installation work, Brain McAdam, Elsevier 4Th Edition.

2. Electrical skills, Ministry Manual.

II. Reference Books

3. “Electrical Engineering, “Allen R Pearson Prentice Hall.

4. “Basic Electrical Installation Work’’, Trevor Linsley, Newness(ACT)

5. “Electrical Installation”, Thompson FG, Longman (NCT), 4Th Edition. 6. “Electrical Technology”, BL Theraja & AK Theraja S Chand Publications.

7. “Residential Construction Academy”, Stephen Herman, Thompson Publisher.

8. “Electrical Instant Answer” Garg Tuck, MC Graw Hill Publications.

III. Web sites

http://www.ehcoman.com

http://www.majanco.co.om


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COURSE ASSESSMENT METHODS

Assessment Scheme (Total Practical Courses)

Course Grading Scheme

Course Passing Grade : 67-69 (C grade)*

* Depends on the course

Marks Grade GPA

90-100 A 4.0

85-89 A- 3.7

80-84 B+ 3.3

76-79 B 3.073-75 B- 2.7

70-72 C+ 2.3

67-69 C 2.0

60-66 C- 1.7

55-59 D 1.0

Below 55 F 0.0

Graduation Grading Scheme

Below grade is displayed in the graduation certificate and it is based on the Overall CGPA ofall levels.

Descriptive GradeGradeOverall CGPA

Excellent A 4

A- 3.7-3.99

Very Good B+ 3.3-3.3.69

B 2.-23

Good B- .-.2

C+ .2-.2

Satisfactory C .2.-.23

Fail

C-

92-92

D 92-923

F 0.0-.99


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Assessment Methods

(Total Practical Courses)

Theory (T) Practical (P)

Not Applicable

Lab report 45 marks

Viva-Voce 15 marks

Written Questionnaire 40

marks

100 % Practical part marks= Total marks out of 100

Assessment scheme for the Lab work

Part I: Lab report with data collection and analysis–

45 Marks

Part II: One Viva-voce – 15 marks

Part III- Written questionnaire – 40 Marks

In this part the student is subject to frequent written questionnaire about the performed

experiments. It may include experimental data collection. A minimum of three written

assessments are to be conducted (i.e. n > 3, where n= no. of practical assessments

conducted). Best of (n-1) performances to be considered for final marks. All written

assessments are announced.


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Attendance:

Issuing of Warning Letter Percentage Number of Hours

First 10%

Second 20%

Third 30%

If the absence reaches 30%, the student will be debarred from the final exam and will

get ZERO in the final exam.

A student will be considered as LATE when s/he arrives after 10minutes of the class

start time. Being LATE for THREE times in a class will be considered as ONE class

absence.

The full course delivery plan must be covered. If students are absent without a valid

reason, it will be considered as if the topic/s is already covered and will be included

in exams.

If a student is absent for two continuous weeks within the semester in all courses,

s/he will be DISMISSED from the College.

Absence Excuse:

If a student failed to attend any class, s/he has to submit the original excuse

document within one week from the date of absence to registration department

only.

If a student failed to attend midterm or final exam, s/he has to fill in aSupplementary Exam Form attached with the original excuse stamped from

concern authorities and submit it to the registration department within one week

from the exam date. Hospital/Clinic Attendance Certificate is not accepted as a

valid excuse.

The coverage of topics in the midterm supplementary exam will include topics

covered up to the midterm exam + topics covered one week after the midterm

exam.

The final complementary exam will be conducted within four weeks from thestart of next semester.


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Course Withdrawal

A student is allowed to withdraw one course during the semester. The withdrawal

period will end a week after the midterm exam resultannouncement.

Submission of Assignment

20% of assignment scored mark will be reduced for each day of late submission.

Cheating

In case of an accusation of cheating during an examination is proven, the following will

be imposed:

Disciplinary Action for Cheating Case/s:

First Offense (Zero Mark)

Second Offense (Study Suspension for one semester)

Third Offense (Dismissal from the College)


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Theory (T) Practical (P)

Not Applicable

Lab report 45 Marks

Viva-Voce 15 Marks

Written Questionnaire 40 Marks100 % Practical part marks= Total marks out of 100

Part I- Lab report with data collection and analysis – 45 marks

No. Factors Marks

1 Ability to follow procedure, data collection 10

2Data analysis, interpretation of results & conclusions related to

the objectives and course outcomes10

3

Completeness, accuracy and

correctness of data and results (Figures, graphs, tables, units,

software)

20

4 Submission on time 05

Total 45 marks

Part II: One Viva-voce – 15 marks

Part II- Written questionnaire – 40 marks

In this part the student is subject to frequent written questionnaire about the performed

experiments. It may include experimental data collection. A minimum of three written

assessments are to be conducted (i.e. n > 3, where n= no. of practical assessments

conducted). Best of (n-1) performances to be considered for final marks. All writtenassessments are announced.

Total weightage for all the above procedures (Part I + Part II+ Part III) is 100%


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WRITING LAB REPORT

1. Each Student has to write a Lab report on each Experiment / Exercise performed &

submit the report within one week.

2. But if the student fails to submit the report within one week, he/she will loose 1

mark each day till the report is submitted.

3.

After the completion of each experiment student must take the signature of course

Lecturer on the cover page.

4.

Attach the cover page to each Lab report before submission.

5.

The report must be written on plane A4 sheets & preferably on both sides of the

paper

6.

Neat report with all the required data, graph, units and conclusion will get better

marks.


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Dos and Don’ts:

Dos:

1. Before starting Laboratory work follow all written and verbal instructions

carefully. If you do not understand a direction or part of a procedure, ASK YOURCONCERN TEACHER BEFORE PROCEEDING WITH THE ACTIVITY

2. Do your wiring, setup, and a careful circuit checkout before applying power.

3. Conduct yourself in a responsible manner at all times in the laboratory. Don’t talk

aloud or crack jokes in lab.

4. Appropriate Personal Protective Equipment should be worn during laboratory

experiments.

5. Do not eat food, drink beverages or chew gum in the laboratory and do not use

laboratory glassware as containers for food or beverages. Smoking is strictlyprohibited in lab area

Don’ts

1. Avoid contact with energized electrical circuits.

2. Do not make circuit changes or perform any wiring when power is on.

3. Do not wear loose-fitting clothing or jewelry in the lab. Rings and necklaces areusual excellent conductors in contact with your skin.

4. Do not touch anything if your hands are wet. The "one-hand" approach is safest.

5. Do not wander around the room, distract other students, startle other students or

interfere with the laboratory experiments of others


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Electrical Accidents/ Hazards are attributed to:

Shock/ Electrocution

Arcing

Fire

Explosion

Which result in:

Loss of Life

Loss of Property

Safety First SAFETY CLOTHING MUST BE WORN SAFETY SHOES MUST BE

WORN

Boys Girls


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Introduction

Electricity and related water sector in Sultanate of Oman

The Law for The Regulation and Privatization of the Electricity andRelated Water Sector (the Sector Law) was promulgated by Royal Decree

# 78/2004 and came into effect on 1 August 2004.

Reference : http://www.ehcoman.com

http://www.ehcoman.com/http://www.ehcoman.com/http://www.ehcoman.com/http://www.ehcoman.com/


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Electricity Distribution in Oman: Geographical Coverage

Reference : http://www.ehcoman.com

Majan Electricity Company: Profile

Majan through its systems, processes and people offers sustainable

management of electricity with the purpose of serving the people of Omanby delivering safe, reliable and economical electricity. *

Reference : http://www.majanco.co.om

http://www.ehcoman.com/http://www.ehcoman.com/http://www.ehcoman.com/http://www.majanco.co.om/http://www.majanco.co.om/http://www.majanco.co.om/http://www.majanco.co.om/http://www.ehcoman.com/


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Regulation Describe about

OES 1 33KV & 11KV Overhead Lines

OES 2 Underground Cables

OES 3 LT Overhead Lines

OES 4 Electrical Installations in Buildings

General Derogation OES 4 clause 6.5 Use of PVC Conduits

OES 5, 5A & 6 Transformers

OES 7, 21, 22, 23, 28 & 31 LT Equipment

OES 8,9,10,16,17,18,20,25, 26, 29 &

33Overhead Line Material & Equipment

OES 11General Specifications Electrical Equipment &

Materials

OES 21A, 12B, 13, 14, 15, 19, 34 & 35 Switchgear & Associated Equipment

OES 24 3311KV Indoor Substations

OES 27 Volume 1 132 33KV Substations

OES 27 Volume 2 132 33KV Substations

OES 30 33 11KV Outdoor Substation

OES 32 132KV OHL

http://www.aer-oman.org/pdf/o2.pdfhttp://www.aer-oman.org/pdf/o3.pdfhttp://www.aer-oman.org/pdf/o4.pdfhttp://www.aer-oman.org/pdf/o4.pdfhttp://www.aer-oman.org/pdf/o5.pdfhttp://www.aer-oman.org/pdf/o5.pdfhttp://www.aer-oman.org/pdf/o4.pdfhttp://www.aer-oman.org/pdf/o3.pdfhttp://www.aer-oman.org/pdf/o2.pdf


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STANDARD OES 4

Ministry of Electricity and Water (now MHEW), Sultanate of Oman has

issued REGULATIONS FOR ELECTRICAL INSTALLATIONS known as

STANDARD OES 4 which is available at

http://www.aer-oman.org

BS 7671:2008

• This British Standard specifies the “Requirements for Electrical

Installations”

• It is also known as IEE Wiring Regulations

• The regulations apply to the design, erection, and verification of

electrical installations.

• These regulations are updated and applicable in the region.


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STANDARD OES 4

Scope and Coverage

(Where to use the standard?)

The regulations apply to electrical installations such as those of,

– Residential Premises

– Commercial Premises

– Public Premises

– Industrial Premises

– Agricultural and Horticultural Premises

– Prefabricated Buildings

– Construction Sites, Exhibitions, Fairs and other temporary installations.

The regulations cover,

– Circuits supplied at normal voltages up to and including 415/240 V AC 50

Hz.

– Any wiring not specifically covered by the specifications of appliances.

– Fixed wiring for telecommunications, signaling, control (excluding external

wiring of apparatus).

Reference: STANDARD OES 4, SECOND EDITION, MAY 1989


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ELECTRICAL STANDARD

Compliance with Regulations

(Why to use/meet the standard?)

Compliance with electrical regulations is essential to ensure safety of life,

plant, equipment and buildings especially from the hazards of fire, electrical

shocks and mishaps in the utilization of electricity in and around buildings.

PROTECTION AGAINST ELECTRIC SHOCK

In electrical installations, one of the major risks is electric shock. Persons and

livestock (animals) shall be protected against dangers that may arise,

a. from contact with live parts of the installation by:

– appropriate measures to prevent contact; ISOLATION

– Limiting the value and duration of current which can pass through a body to

a value lower than shock current. INSULATION

b. From contact with exposed metal parts by one of the following methods.

– Preventing a fault current from passing through the body of any person or

any livestock. EARTHING

– Limiting the value and duration of current which can pass through a body to

a value lower than shock current. INSULATION

– Automatic disconnection of the supply on the occurrence of a fault likely tocause a current to flow through a body in contact with the exposed metal

parts, where the value of the current is equal to or greater than the shock

current . ISOLATION

PROTECTION AGAINST THERMAL EFFECTS

Another major risk with the electrical installations is excessive temperature

likely to cause burns, fires and other injurious effects.

Protection shall be provided against

– The harmful effects of heat or thermal radiation developed by electricalequipment.

– Ignition, combustion or degradation or material.

Reference: BS7671-2008

– flame and smoke where a fire hazard could be propagated from an electrical

installation to other nearby fire compartments and


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– Safety services being cutoff by the failure of electrical equipment.

PROTECTION AGAINST OVERCURRENT

Persons or livestock shall be protected against injury and property shall be

protected against damage due to excessive temperatures or electro-mechanical

stresses caused by over currents likely to arise in live conductors by,

– Automatic disconnection on the occurrence of over-current before the over-

current attains a dangerous value taking into account its duration.

– Limiting the maximum over-current to a safe value and duration.

Conductors other than live conductors and any other parts intended to carry a

fault-current shall be capable of carrying that current without assuming excessive

temperature.

PROTECTION AGAINST VOLTAGE DISTURBANCES AND ELECTROMAGNETIC

DISTURBANCES

Shall cover,

– Protection of low voltage installations against temporary over-voltages due

to earth fault in high voltage systems and due to faults in the low voltage

systems.

– Protection against over-voltages of atmospheric origin or due to switching.

– Measures against electromagnetic influences.

– Protection against under voltages

Reference: BS7671-2008


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Compliance with OES4 is achieved through following steps:

(How to meet the Standard?)

1. Submission of Drawings: Schematic and wiring diagrams, layout drawings and

schedule of points with site layout should be submitted to the Ministry beforecommencement of any electrical work whatsoever large or small, new or

additions, and work shall start only after due approval of the Ministry. All work

should be carried out in accordance with the approved drawings.

2. Inspection: All installation work will be subject to inspection and testing by the

ministry and will be connected to the power supply only after the work is

checked and approved by the ministry.

3. Electrical Supervision: All electrical installation works shall be carried out by or

under the direct supervision of a qualified electrical engineer or a supervisor

holding a competency license issued by the Ministry. Such competency licensewill be issued after necessary tests and interview by the Ministry.

4. Standards, Materials and Workmanship: The works shall be carried out in a

neat and workmanlike manner to meet the requirements of these regulations. All

materials used shall be the best of their respective kinds and shall comply with

the latest relevant recommendations of the International Electro-technical

Commission (IEC) if available and if no IEC recommendation is available with the

latest relevant British Standard Specification (BSS)

Reference: STANDARD OES 4, SECOND EDITION, MAY 1989


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Exercise 1: Electrical Supply

Aim: To understand different types of supply systems and trace the electrical supply

system in Shinas College of Technology

(After discussion of the topic in class the students will be taken around the campus

of the institute to trace the electrical supply system)Electrical Power System in Oman:


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Electrical supply at the consumers (domestic/ commercial/ industrial) is drawn from

distribution substations. Depending on the applications and KVA the supply voltage is

11kV or 400 V. The distribution substations are equipped with necessary means for

isolation and protection.

Bulk consumers of electricity such as Shinas College of Technology receive electrical

supply at 11kV from distribution substation.

In the consumer premises, the consumer has another substation to step down this

voltage to 400V to meet lighting and low voltage applications.


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S c h e m a t i c d i a g r a m o

f s u c h a

s y s t e m i

s d i s p l a y e d i n t

h e f o l l o w i n g d i a g r a m :


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Exercise 1: Electrical Supply Systems:

Reference:

Chapter 7, Advanced Electrical Installation Work, Fifth Edition,

Publication: Newens

Author: Trevour Linsley

As per the Electricity Regulations applicable in the region to ensure safety, electrical

installations must be equipped with

1. Basic protection and2. Fault protection

This protection is provided using principle of “Protective equi-potential bonding

coupled with automatic disconnection of supply”. In this method all exposed metal

work is electrically connected together to an effective earth connection.

This expose metalwork includes,

Electrical conduits

Trunking

Metal switches

Metalwork of electrical appliances

Water service pipes

Gas and other service pipes and ducting

Central heating and air conditioning systems

Exposed metallic structural parts of the building

Lightening protective systems


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There are three commonly used arrangements of the earthing connection as described

in IEE Electricity Regulations which are discussed here.

TN-S System

TN-C-S System TT System

These have been designated in the IEE Regulations using the letters: T, N, C

and S. These letters stand for:

T - terre (French for earth) and meaning a direct connection to earth.

N - neutral

C - combined

S - separate.

When these letters are grouped, they form the classification of a type of system.The first letter denotes how the supply source is earthed.

The second denotes how the metalwork of an installation is earthed.

The third and fourth indicate the functions of neutral and protective conductors.


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TN-S System (Cable Sheath Earth Supply)

Used where the electricity company’s supply is provided by undergroundcables.

Neutral and protective conductors CP (also called as protective earth PE) are

separate throughout the system.

The protective earth conductor (PE) is the metal sheath and armour of theunderground cable and this is connected to the consumer’s main earthing

terminal.

All exposed metalwork is connected to the protective conductor via the main

earthing terminal of the installation.


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This system has the neutral of power supply with connection of earth only atone point to the source. The consumer’s earthing terminal is usually connected

to the metallic Armour of the distributor’s cable into the HV / LV transformer.

It is commonly used for underground power supply to the premise or factory

from the distributor substation to customer substation. This earth terminal is

connected by the supply protective conductor (PE) back to the star point

(neutral) of the secondary winding of the supply transformer, which is also

connected at that point to an earth electrode.

http://www.electricneutron.com/tag/cable/http://www.electricneutron.com/tag/cable/http://www.electricneutron.com/tag/cable/


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TN-C-S System (Protective Multiple Earthing Supply)


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The supply cable uses a combined protective earth & neutral (PEN) conductor.

At the supply intake point a consumer’s main earthing terminal is formed byconnecting the earthing terminal to the neutral conductor.

All exposed conductive parts of the installation are then connected to the mainearthing terminals. Thus phase to earth faults are effectively converted into

phase to neutral faults


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TT System (No Earth Provided Supply)

installations protective conductor must be connected to earth via an earth electrode

provided by the consumer. The TT method is used mostly in country areas with

overhead transmission lines.

In contrast to the TN-S system there is no metallic path from the consumer's terminals

back to the sub-station transformer secondary windings. Because the earth path may beof high resistance, a residual current circuit-breaker (R.C.C.B.) is often fitted so that if a

fault current flows in the earth path then a trip disconnects the phase supply.

For protection against indirect contact in domestic premises, every socket outlet

requires an RCCB with a maximum rated current of 30mA.


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Residual Current Protection

RCDs are designed to disconnect the circuit if there is a leakage current. By detecting

small leakage currents (typically 5–30 mA) and disconnecting quickly enough (


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Advantages

1. They are less sensitive to fault conditions.2. While voltage and current on the earth line is usually fault current from a live wire,

this is not always the case, thus there are situations in which an ELCB can nuisance

trip.

3. When an installation has two connections to earth, a nearby high current lightningstrike will cause a voltage gradient in the soil, presenting the ELCB sense coil with

enough voltage to cause it to trip.

4. If the installation’s earth rod is placed close to the earth rod of a neighboringbuilding, a high earth leakage current in the other building can raise the local

ground potential and cause a voltage difference across the two earths, again

tripping the ELCB.

5. If there is an accumulated or burden of currents caused by items with loweredinsulation resistance due to older equipment, or with heating elements, or rain

conditions can cause the insulation resistance to lower due to moisture tracking. If

there is a some mA who is equal to ELCB rating than ELCB may give nuisance

Tripping.

6. If either of the earth wires become disconnected from the ELCB, it will no longer tripor the installation will often no longer be properly earthed.

7. Some ELCBs do not respond to rectified fault current. This issue is common forELCBs and RCDs, but ELCBs are on average much older than RCB so an old ELCB is

more likely to have some uncommon fault current waveform that it will not

respond to.8. Voltage-operated ELCB are the requirement for a second connection, and thepossibility that any additional connection to earth on the protected system can

disable the detector.

9. Nuisance tripping especially during thunderstorms.


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Disadvantages

1. They do not detect faults that don’t pass current through the CPC to the earth rod. 2. They do not allow a single building system to be easily split into multiple sections

with independent fault protection, because earthing systems are usually use

common earth Rod.3. They may be tripped by external voltages from something connected to the

earthing system such as metal pipes, a TN-S earth or a TN-C-S combined neutral

and earth.

4. As electrically leaky appliances such as some water heaters, washing machinesand cookers may cause the ELCB to trip.

5. ELCBs introduce additional resistance and an additional point of failure into theearthing system.

Answer following questions:

1) Why and where protection is required in the Electrical Installations?

2) Where we can use the earthing systems?

a) TN – S System

b) TN – C – S System

c) TT System

3) What is RCD? How does it work?

4) What is the supply voltage obtained from the electricity board to Shinas college of

Technology?

5) What is the kVA rating of the distribution substation in the college premises?

6) What is the type of transformer in the substation?

7) How much voltage is required at the consumer’s premises for Lighting and low

voltage applications?


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Exercise 2: Measurement of the Earth Resistance

STANDARD, OES4

Section 4.2.9

CONSUMER EARTING SYSTEM

An independent, separate earthing system shall be installed and maintained by

the consumer. This shall comprise the following,

Earth electrode of 15mm diameter copper earth rod set with driving pin

and head driven to a minimum depth of 3 meters. This shall be installed as

near to the consumer’s main board as possible inside earth pit with

inspection cover as per figure 2.1. The earth electrode shall include a

corrosion resistant terminal clamp. PVC insulated stranded copper earth conductor (35 mm 2 copper for single

consumer installation and 70 mm 2 copper multiple consumer

installation) with cramped terminal lugs, shall be connected between the

earth electrode and the consumer’s main earthing terminal or bar.

PVC insulated earth continuity conductor of every outgoing circuit from

the consumer’s main board shall be connected to the main earthing

terminal.

The resistance of the consumer’s earthing system to the general

mass of earth shall not exceed 50 Ω. To achieve this value in theareas of high soil resistivity, additional earth electrodes with a

minimum spacing of 3 meters shall be installed.

Consumer’s earth electrode resistance shall be measured in accordance

with the method described in Appendix VI of the OES4.

All metal work, exposed conductive parts and enclosures, in the

consumer’s installation (other than live conductors and current carrying

parts) shall be connected with PVC insulated earth continuity conductor

to the main earthing terminal.

The consumer’s earthing system shall be connected to the MEW(electricity Distribution Company) earthing system.

The neutral conductor shall remain insulated throughout the installation

and shall not at any point be connected to the earthing system.


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(Note: all dimensions are in mm)

Figure 2.1: Earth Pit


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Aim: To measure the value of earth resistance and earth voltage by using Earth

Resistance Tester (Kyoritsu 4102A).

Apparatus Required:

1) Earth resistance tester - 1 No.

2) Connecting leads - 3 Nos.

3) Earth Electrodes - 2 Nos.

4) Hammer - 1 No.

Theory:

The importance of earthing lies in the fact that it deals with safety. The word

‘earthing’ comes from the fact that the technique itself involves making a low-

resistance connection to the earth or to the ground. The earth is considered to be a

large conductor which is at zero potential.

Reason for Earthing:

The basic reason for earthing is to prevent or minimize the risk of shock to human

beings and livestock by providing a low resistance discharge path for earth leakage

currents which would otherwise provide injuries or even death to a person or animal

touching the metal part.

The following diagram describes the degree of danger of the leakage current; if, it

flows in the human body.


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The following example through the figures describes how the earthing system works:

In the following diagram the metallic part is not earthed and the human being is

touching it.

Let,

The supply voltage is 240V, AC circuit. The apparatus is having 40Ω and the defectiveinsulation is making the metallic body live and it is not earthed. Let the body

resistance is 1000Ω:

As shown above the leakage current may cause death to the person that is in contact

with the metallic part. The fuse in the path will not be able to identify the small rise in

current.

In the following diagram the metallic part is earthed and the human being is touching

it.

With the same supply system let, the sum of the resistance of cable and the metallic

part be 10Ω

Now the current is 4.8 times the fuse rating current. So, the fuse will operate andprotect the human by:

i. Blowing out and separating the supply from the body in touch with the

equipment

ii. By making the potential across the body ‘Zero’ (i.e. a shorted electric part

through the earth wires).


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Types of earth electrodes:

Rod and pipe electrodes:

The following drawing describes how such electrodes are used in a distribution

wiring system:

Plate electrodes:


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The following drawing describes how such electrodes are used in a distribution

wiring system:


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Preparation for Measurement:

A)

Mechanical Zero Adjustment

To obtain a measurement value with high accuracy, rotate the meter zero adjuster

with a screwdriver with the range selector switch OFF, and surely match the

indicator to “0” graduation value at the left of the scale board.

B)

Connecting Test ProbeInsert the plug of the probe securely into the terminals of the instrument. Loose

connection may result in inaccurate measurements.

C)

Battery Voltage Check

Set the range selector switch to BATT.CHECK position and press the test button.

Then the indicator swings, make sure that the indicator is at the right of BATT.GOOD

graduation borderline on the scale board. Otherwise, the batteries are exhausted.

Connection Diagram:


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Procedure:

1) Strike the auxiliary earth spikes P and C into the ground deeply. They should be

aligned at and interval of 5 -10 meters from the earthed equipment under test.

2) Connect the Green Wire to the earthed equipment under test, Yellow to the

auxiliary earth spike P and the Red to the auxiliary earth spike C from terminals E,

P and C of the instrument respectively.

3) Set the range switch to EARTH VOLTAGE position to check earth voltage. Record

the reading in table below.

4) Set the range switch to × 100 positions, and press the test button. The LED

remains illuminated during testing. Turn the range switch to × 10 and × 1

when the earth resistance is low. This indicated value is the EARTH RESISTANCE of

the earthed equipment under test.

5) Change the spike ‘P’ position to 2m, 4m, 6m, 8m, 10m from the earth pin ‘E’ and

note down the earth resistance and tabulate the readings.

Observations:

Distance From the Earth

Pin ‘E’ to the Spike P

Earth Resistance Observed

Value (Unit)

2 m

4 m

6 m

8 m

10 m


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Graph

The variation of earth resistance with distance

Conclusions:

Answer Following Questions,

Why is it necessary to provide earthing?

From the observations above, comment if the earth resistance measured is

acceptable as per the OES 4.

If the value of resistance is unacceptable, what are the measures required to bring itto the acceptable range?


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Exercise 3: Preparation of Galvanized Steel Conduit

STANDARD, OES 4

Section 3.13

Steel Conduits and fittings for use in building electrical installations shall

comply with BS 4568, Parts 1 and 2 of heavy gauge hot dip galvanized inside

and outside, screwed type.

Section 6.1

Installation of Conduits

The conduits for each circuit shall be completely installed before any cable is

drawn in.

Conduits shall be securely fixed and where they are liable to mechanical

damage they shall be adequately protected.

Provision for the safe and easy drawing in of cables shall be made by use of

inspection fittings, draw boxes. Provisions shall be such that cables can be

drawn in or replaced without the cables being damaged or conduit

dismantled.

All runs of the conduit shall be truly vertical or horizontal.

Section 6.2

Conduit Saddles

Where conduits are installed on the surface of building fabric they shall be

supported by purpose made conduit saddles or spacer bar saddles.

Supports shall be provided at a maximum spacing of 1500 mm for

galvanized steel conduits and 1200 mm for high impact PVC conduit.

Section 6.3

Smooth Finish of Conduits

The boxes of all the conduits shall be smooth and free from projection which

may injure cables or obstruct their drawing in. ends of conduits shall be so

reamed and when they terminate at boxes, trunking and accessories not fitted with spout entries, shall be so bushed as to obviate abrasion of cables.


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Section 6.4

Radius of Bend

The radius of every conduit bend shall not be less than 2.5 times the outside

diameter of the conduit.

Section 6.5

Galvanized Steel Conduits

Galvanized Steel conduit system shall be earthed and connected to the earth-

continuity conductor. All joints shall be made mechanically and electrically

continuous by screwing. The conduit shall not however be used as an earth

continuity conductor and a separate earth continuity cable shall be drawn

into the conduit for every final sub-circuit.

Only Galvanized Steel conduits shall be used in the space between a roof and

suspended false ceiling, in situations subject to fire risk and in surface

mounted industrial installation. PVC conduits shall not be used for such

applications. (Derogation issued in2009 to use PVC conduits)

Galvanized Steel conduits shall not be used under floor tiles of buildings or in

concealed wiring systems embedded in walls or floors. PVC conduits shall be

used for all such applications.

Section 6.6

PVC Conduits and Fittings

PVC conduits and fittings shall be of the unthreaded type. All joints shall be

made with vinyl cement and entries of all conduit fittings shall be designed

such that reliable water tight joints can be obtained.

Surface mounted PVC conduit systems shall be so supported as to allow for

longitudinal expansion and contraction. A cement that shall remain in

adhesive plasticized state shall be used for expansion couplers.

Section 6.7

Flexible Conduits

Flexible conduits shall only be used for the final connection of motors and

other equipment subject to vibration or adjustment of position.

PVC flexible conduits and fittings shall comply with BS 4607 part 3. Metallic

flexible conduits and fittings shall comply with BS 731 Part 1 and shall

preferable be provided with an outer sheath of PVC.

Flexible metal conduit shall not be used as the sole means of providing earth

continuity and a separate earth continuity cable shall be provided.


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Where necessary, flexible conduit shall be adequately supported and / or

protected.

In damp or wet situations flexible conduits shall be watertight and remain

impervious to ingress of water or moisture.

The ends of flexible conduit shall be securely anchored to fixed conduit and /or equipment entries by purpose made flexible conduit adaptors.

Section 6.8

Conduit Sizes

Conduits shall be limited to the following sizes

16 mm, 20 mm, 25 mm, 32 mm and 50 mm


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Aim: To make the Galvanized Steel conduit to do the wiring for the following

measurement.

1) Making 900 bend from a fixed point.

2) Making two 900 set.

3) Making thread for 1.5 cm at one end.

Tools Required:

1) Steel Pipe Bending Vice - 1 No.

2) Steel Pipe - 1 No.

3) Threading Die - 1 No.

4) Hand File - 1 No.

5) Wire Brush - 1 No.

6) Measuring Tape - 1 No.

7) Marker Pen - 1 No.

Cutting:

Conduit pipes can be cut by using a hacksaw or a pipe cutter as shown in the following

figures:

Procedure:

1. Fix the conduit in the vice so that the vice grips the conduit 50 or 75mm from the

point where the cut has to be made

2. The blade is to be installed so that the cut is made on the forward stroke.

Precautions:a. After cutting by any method the inside edge

of the conduit must be smoothed with half

round file as shown in the figure.

b. Be sure that the ridge is cleared beforeinstalling the pipe for wiring.

c.


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Threading:

When short lengths of conduits are to be used for switch or lamp drops, the end of

the pipe needs to be threaded to enable fixing of the conduit to the accessories. The

threads on the conduit in all cases shall be between 11mm to 27mm long.

This threading of conduit is done by using dies and a die-stock.

Note:

1. Apply cutting oil to the end before starting to cut threads.

2. Cutting threads longer than necessary will leave exposed threads that are not

protected from corrosion.

Precaution:

a. Use only a brush to remove the metal burrs from the die. Do not use your hand.

Metal conduit boxes and the symbols used in metal conduit wiring:

The following figure shows different popular outlet boxes used in metal conduitwiring:


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Following figure shows the various symbols used for different boxes in a single line

diagram for such a wiring:

The following figure shows the wall and ceiling boxes for conduit wiring, a switching

box is also displayed:


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Preparing the boxes for the conduit wiring:

The boxes can be used after removing the knock-outs in the boxes. The knock-outs

can be removed from the boxes by using any of the method shown in the following

figures:

After removing the knockouts the boxes are prepared as shown in the following

figure:


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Conduit pipe bending:

It is often necessary to set or bend the conduit to enable it to pass over an

obstruction as shown in the following figure:

The bending can be made by using:

a. Simple bending block:

b. Simple bending hickey:


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c. Using a bending machine:

60 mm80 mm

mm63

8

160

8

d

d = outer diameter of

the bending pulley

Actual radius of bend =

inner radius of the pulley

Pulley


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Procedure:

1. Measure diameter of the Galvanized Steel Pipe given for the exercise.

2. Select suitable pulley for bending the pipe.

3. Making 900 bend from a fixed point.

1) Take a steel pipe of length 900 mm and mark 300 mm from the edge or a fixed

point consider that mark as an initial mark.

2) Add th8

1 of the outer circumference of the bending pulley from the initial mark

Example: 300mm + ( 8

160

) =363 mm and consider this as a new mark.

3) Place the tube in the former with the fixed point at the rear and place the pipe

exactly at the new mark which should be aligned with the perpendicular scale.

4) This will give a 900 bend at the required distance from the fixed point to the back

of the bend.

4. Making two 900 set:

1) From initial mark of 300 mm, measure another 300 mm and mark.

900

300

300 63 mm

300

mm


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2) Take this new mark as reference, subtract th8

1 of the outer circumference of the

bending pulley. Consider this as reference mark for the second bend.

3) Now measure the gap between two bends. If you get 300mm from center to

center of the bends means your work is carried out successfully.

5. Making thread at one end:1) Mark the threading length in the steel pipe from the fixed end. Take the die and

fix it with the tool used for making the thread.

2) Place the threading tool at the edge of the pipe and rotate it in forward direction

for one full circle and rotate in opposite direction for one full circle.

300

mm

300 mm

63 mm

300mm

300 mm

300

mm


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3) Repeat the same thing until the full thread is made at one end as per the

measurement.

Results:

1. Mention the various types of conduits.

2. What are the available sizes of conduits used in industry?

3. Mention the applications of various types of conduits.

4. Mention the precautions taken while performing the exercise?

S.No Quantity Measurement

1 Length of pipe used

2 Size of Pipe used

3 The angle made at one end

4 The angle made at other end

5 Radius of the bend

6 Distance between the bends

7 Distance from one end to center of the bend


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Exercise 4: Wiring Lighting Circuit

STANDARD OES 4

Section 4.2.10

Connection of Switch and Control Gear

Switches, circuit breakers, fuses, thermostats and similar control devices shall

be connected in live (phase) conductor only, a bolted or screwed link being

connected in the neutral conductor. If the switch or circuit breaker includes an

isolating neutral link, it shall be arranged to make before and open after the

live (phase) poles.

Section 4.2.17

Load on lighting circuits

Load on lighting circuits in domestic installations shall not exceed 1500 W per

final sub circuit.

Section 4.2.20

Lighting Switches

Local switches for lighting points and for appliances not connected to socket

outlets shall have a minimum current rating of 5A. For outdoor and industrial

use, switches shall be metal clad and water tight.

Switches for control of discharge lighting shall have a current rating of not less

than twice the steady state continuous current of the circuit.

All local switches shall be mounted in readily accessible positions with the

dollies at the minimum height of 1250 mm from finished floor level.

In kitchens and in situations other than bathrooms, where water is regularly

used no switch shall be mounted within 2 meters of any tap, basin, sink, if this is

not possible, ceiling mounted insulating cord operated switches shall be used.

In bathroom and toilets, switches shall be of the ceiling mounted insulating

cord operated type. If wall mounted switches are used for control of lighting

and exhaust fans, same shall be located in an accessible position outside the

bathroom or toilet and immediately adjacent to the door. Special wall mounted

switch for control of supply to water heater shall be similarly mounted.

Switches for lighting and fans inside a room shall be mounted inside the room

on the side of the door nearest to the door catch, handle knob or lock

approximately 150mm from the door frame.


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Section 5.2

Current Ratings

Current Ratings for single core and multicore cables to be adopted for use in

consumer’s installation are set out in tables 2, 3, 4 and 5 (Appendix IV) of OES4.

The current carried by the cables at any time shall not exceed the specified

ratings.

Section 5.4

Protection against damage

All conductors and cables shall be adequately protected against any risk of

mechanical damage to which they may be liable in normal condition of service.

Where cables pass through hole in metal works, rubbers or plastic grummets or

bushes shall be provided of the edge lined with soft material to prevent

abrasion of the cables.

Section 5.18

Flexible cord and cables

Current ratings for flexible cords and cables are set out in Table 1 (Appendix IV)

of OES4.

Where the apparatus requires to be earthed, flexible with earth core shall be

used.

Where the flexible cables and cords are exposed to the risk of mechanical

damage, they shall as a minimum be sheathed with PVC or rubber and where

necessary shall be armored, the armour not being used as sole means of

providing earth continuity.

Flexible cords and cables shall be connected to plugs, ceiling roses and movable

apparatus with the BROWN core to phase, BLUE core to neutral and

GREEN/YELLOW core to earth terminal of accessory or frame of the apparatus.

In situations where high temperatures are encountered, flexible cables and

cords shall be insulated with silicon rubber type E12 of BS6899/IEC540

Where a flexible cord supports or partially supports a luminaire, the maximum

mass supported by the cord shall not exceed the values given in Table 1

(Appendix IV)


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Section 5.19

Colour identification of cable cores

a.

Colour identification of insulated cable cores for fixed installation and of

sleeve, band or disc for bare conductors shall be as follows:

- earthing conductor green and yellow

- phase of a.c. single phase circuit red

- neutral of a.c.single phase or three phase circuit black

- phase R of three phase a.c. circuit red

- phase Y of three phase a.c. circuit yellow

- phase B of three phase a.c. circuit blue

- positive of d.c. 2 wire red

- negative of d.c. 2 wire black

b. Colour identification of flexible cables and flexible cords shall be as follows:

- live brown

- neutral blue

- earthing green and yellow

Mounting Heights of Accessories

Item Height from finished floor level

Lighting Switch 1250 mm

Ceiling Fan Regulator 1250 mm

20Amp, D.P switch for water heater or A/C units 1250 mm

Shaver socket outlets 1250 mm

13Amp switched socket outlet for general purpose 450 mm

13Amp switched socket outlet in kitchen 250 mm

Cooker control unit 1000 mm


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Symbols of Electrical Accessories – (Appendix 3 of OES 4)


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Aim : To connect two lamps in parallel

Objectives:

1) Knowing the OES 4 and its sections pertaining to wiring at different installations

2) Category of load as per OES 4

3) Standards pertaining to wiring of a building for a normal household consumer

4) Standard pertaining to voltage drop, current rating, parallel operation and

protection against damage.

5) Practice of wiring for a normal parallel connected load for domestic application.

Tools Required:

6) Electrical / Manual Driller

7) Screw Drivers

8) Hacksaw frame with Blade

9) Wire Stripper

10) Pliers

Accessories Required:

1) PVC Conduit

2) Conduit Saddles and Screws

3) Elbow or Bend

4) Junction box5) Lamp Holders with Lamps

6) Single pole switch

7) Miniature Circuit Breaker (MCB)

8) Earth Leakage Circuit Breaker (ELCB)

9) 15 Amps , 1 Way Terminal Box

Measuring Instruments:

Multi Meter for measurement of current and voltage


70/112



Circuit Diagram:

Line Diagram:

Single Phase240 V, 50 Hz

L

N

S

L1 L2

E

Distribution

Board ELCB MCB Switch

Lamp 1

Lamp 2


71/112



Layout Diagram:


72/112



List of Material:

Sr. No. Item SpecificationQuantity

Required

1 Conduit

2 Saddles

3

Cable Red

Cable Black

Cable Yellow and Green

4 Switch

5 Junction box

6 Elbows or Bends

7 Lamp holder

8 MCB

9 ELCB

10 Lamp1

11 Lamp2

12 Clamp meter


73/112



Procedure:

1) Connect the items collected per the layout diagram on the work board.

2) Check the tightness of the connections.

3) Never forget to verify the tracing of the wires as per the layout diagram.

4) CHARGE THE CIRCUIT UNDER THE SUPERVISION OF TECHNICIAN.

5) Verify the live terminal at input of the ELCB using line tester.

6) Switch ON the ELCB and using line tester observe that the circuit is live and the

wiring is perfect.

7) Switch on the MCB and observe that the wiring is working perfect.

8) Similarly check that the live terminal at the Lamp Holders turns Live, only on

making the switch ON.

9) Note the Operation of the circuit by visual inspection and record the data in

your report.

10) Note down the reading of Voltage and current in the observation table and

calculate the power.


74/112



Measurements and Calculations:

Sr. No. Condition Voltage (V) Current (I)

1

Only Lamp1

(______W,______V)

2Only Lamp2

(______W,______V)

3 Lamp 1 and 2

Calculations:

SlNo

Specification Voltage V

CurrentI

Power

Consumed (P)

1 Lamp 1 (alone): ______W

2 Lamp 2 (alone): ______W

Result: Write how the activity performed meets the requirements of various

sections of OES referred at the beginning of this experiment.

Answer the following questions.

1. What is the use of MCB in the circuit?

2. What is the use of ELCB in the circuit?

3. By observing the Currents drawn by the circuit and bulbs, How the bulbs

are connected?4. What is the use of earth terminal in the circuit?


75/112



5. Exercise 5: Testing Wiring Circuits

GUIDELINES FOR TESTING WIRING CIRCUITS AND CERTIFICATION OF TESTING

The Oman Electricity Standard, OES 4 in Section 11 guides on the testing and inspection of

the electrical installation.

STANDARD, OES4

Section 11.1 General

Every installation and major alteration to an existing installation shall on

completion and before being energized, be inspected and tested to verify

compliance with MEW regulations.

Section 11.2 Visual Inspection

A visual inspection shall be carried out to verify if the installation is in

accordance with approved drawings and the execution of the work andworkmanship and the installation methods adopted meet the requirements of

the MEW regulations.

Section 11.3 Colour Identification

It shall be verified that the correct colour identification has been adopted for all

wiring and the fuses and switches are connected in the live conductors only and

links or linked switches are connected in the neutral conductor.

Section 11.4 Earth Continuity Test

Earth continuity test shall be carried out between the consumer’s earthing

terminal and the remote end earth continuity conductors.

The resistance value obtained shall not exceed 0.5 ohm.

Section 11.5 Insulation Resistance Test

Insulation resistance test shall be carried out on the installation. For purpose of

these tests large installations must be divided into groups each containing 50

outlets. A 500V DC test voltage shall be applied.

The insulation resistance to the earth shall not be less than 1 mega ohm, when

measured with all poles and phases of wiring connected together and switchesand fuses all in place. The insulation resistance when measured between all the

conductors connected to any one pole or phase of supply and in turn all

conductors connected to each other pole or phase shall not be less than 1 mega

ohm.


76/112



Section 11.6 Continuity Test

Test shall be made to verify the continuity of all conductors including the earth

continuity conductor of every ring circuit.

Section 11.7 Earth Electrode Resistance Measurement

Earth Electrode Resistance Measurement shall be carried out in accordance

with method described in Appendix VI. The resistance shall not exceed 50 Ohms.

Additional electrodes shall be provided where necessary to obtain this value.

Section 11.8 Protection Test

Tests shall be carried out to verify effective and correct operation of all earth

leakage circuit breakers, close excess current protection of circuit breakers and

fuse links and other protective devices.

Section 11.9 Completion CertificateFollowing the inspection and testing, a completion certificate in the attached

format shall be submitted by the electrical contractor to MEW signed by

contractor’s competent engineer. The installation will then be further inspected

and tested by MEW inspector and if found satisfactory, the installation will be

permitted to be connected to supply.


77/112



COMPLETION CERTIFICATE

(Completion certificate to be given by the Electrical Contractor and signed by

Contractor’s Competent Engineer/ Supervisor):

I hereby certify that the electrical installations at:

has been completed, inspected and tested in accordance with the regulations

for electrical installations issued by the Ministry of Electricity and Water,

Sultanate of Oman and is now ready for connection to mains supply.

The results are given in the attached forms.

Signed: ___________________________________ Date:__________________

For and on behalf of : _____________________________________________

_______________________________________________

_______________________________________________

Address: ______________________________________________

________________________________________________

_______________________________________________

MEW Registration No. and Date: _____________________________________


78/112



FORM A

Particulars of the installation covered by this Certificate:

New Installation. Alteration / Extension to existing installation.

Installation Drawing:

It is anticipated that the installation would comprise the following:

S. No. Description No.kW

Unit Total

1 Light Points

2 Air conditioners

3 Fans

4 Single Phase Motors

5 Three Phase Motors

6 Water Heaters

7 Refrigerators

8 Freezers

9 Cookers

10 13 A Socket Outlets

11 Other Loads

12 …………………………………

13 …………………………………

Comment (if any) on existing installation (where the certificate relates to an

alteration or addition)

Signed:____________________________________ Date:_________________


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FORM B

INSPECTION AND TEST REPORT

1. Compliance with drawings:

2.

Standard of Installation:

Material:

Workmanship:

3.

Colour identification of wiring:

4.

Polarity Checks:

Switches:

Breakers:

Links:

Linked Switches:

5. Resistance of Earth Continuity

Conductor from remote end to

main earthing point:

6.

Insulation Resistance:

- With all poles and phases

connected together and

switches, fuses and breakers

all in place

- With all conductor on one

phase connected together

and in turn all conductors

connected to each other.

– Red:

– Yellow:

– Blue:

– Neutral:


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7. Continuity of all Conductors

- Red:

- Yellow:

- Blue:

- Neutral:

- Earth:

8.

Continuity of earth continuity conductor in ring circuit for socket outlet.

9. Earth Electrode Resistance:

10.

Earth Leakage Circuit Breakers(Residual Current Operated Type)

Continuous Rating Operating Current

(A)

(mA)

Main Subsidiary 1)

2)

11. Load Balance

Red Yellow Blue

- Lights

- Refrigerators

- Air conditioners

- Freezers

- Cooker

- Motors

- Water Heaters

- 13A Socket Outlet

- Other Loads

Signed:_____________________________________ Date:_________________


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Objectives: At the end of the exercise the student should be able to understand the

following:

1) Understanding the need for Testing and Inspection of wiring in electricalinstallations

2) Understanding the different types of Testing and Inspection procedures as perOES 4

3) Preparing ‘Completion Certificate’ pertaining to Testing and Inspection ofelectrical wiring as per OES 4

4) Inspection & Testing procedure required to follow as per OES 4, for a givenelectrical circuit.

Aim : To Connect a 3 Pin Plug connection and perform following tests

1) Visual inspection

2) Color Identification

3) Earth Continuity Test

4) Continuity Test and

5) Protection Test

Tools Required:

1) Electrical / Manual Driller

2) Screw Drivers

3) Hacksaw frame with Blade

4) Wire Stripper

5) Pliers

6) Line Tester


1) Conduits

2) Conduit Saddles and Screws

3) Elbow or Bend

4) Red, Black and Yellow/ Green Cable

5) Junction box6) 3 Pin Plugs with Switches

7) Miniature Circuit Breaker (MCB)

8) Earth Leakage Circuit Breaker (ELCB)

9) 15 Amps , 1 Way Terminal Block


82/112



Measuring Instruments:

Multi Meter (KYORITSU KEW SNAP 2017)


83/112



Circuit Diagram:

Line Diagram:

Single Phase

240 V, 50 Hz

AC Supply

DistributionBoard

ELCB

MCB 1

Switch Socket

Outlet 1

MCB 2

Switch Socket

Outlet 2


84/112



Layout Diagram:


85/112



List of Material:

Sr. No. Item SpecificationQuantity

Required

1 Conduit

2 Saddles

3 Elbows or Bends

4

Cable Red

Cable Black

Cable Yellow and Green

5 Switch Socket Unit

6 Junction box

7 Terminal Box

8 MCB

9 ELCB

10 Clamp meter


86/112



Procedure:

Visual Inspection Test:

Observe the following points in this test and write observations.

1. The installation is as per the layout diagram.

2. The installation comprises of the protection devices as shown in the line

diagram.

3. Accessories used are of standard quality and note down the standards printed

(if any)

4. Connections and joints of the cable are firm/ tight and appropriately insulated.

5. Cables are protected against mechanical damage.

6. Switches are mounted at a minimum height of 1250 mm from finished ground

surface.

Colour Identification:

Observe that appropriate colour code is used in the electrical installation. Write the

observations below,

1. Colour of the cable used for Live/ phase wire:__________________

2. Colour of the cable used for Neutral wire: _____________________

3. Colour of the cable used for Earth wire: _______________________

Earth Continuity Test:

Write observation in the table below.

Sr.

No.Connection of the multimeter

ObservationComment

Sound Resistance

1

Earth terminal of Socket Outlet

1 and Earth terminal of the

Distribution board

2

Earth terminal of Socket Outlet

2 and Earth terminal of the

Distribution board


87/112



Continuity Test:

Sr.

No.Connection of meter

ObservationComment

Sound Resistance

1 Line terminal of outlet 1 and Lineterminal of outlet 2

2Neutral terminal of outlet 1 and

Neutral terminal of outlet 2

3Line terminal of outlet 1 and Line

terminal of Distribution Box

4

Neutral terminal of outlet 1 and

Neutral terminal of Distribution

Box

5Line terminal of outlet 1 andEarth terminal of Distribution Box

6Neutral terminal of outlet 1 and

Earth terminal of Distribution Box

Protection Test:

Press the test button of the ELCB and note your observation:


88/112



Answer the following questions

1. What is Visual Electrical Inspection?

2. Explain color identification procedure for electrical installation

3. What is Earth continuity test?

4. What should be the Insulation resistance as per OES-4?

5. What is continuity test?

6. How much should be the earth resistance as per OES -4?


89/112



Exercise 6: Connection of Fluorescent Tube Light

Objectives: At the end of the session the student should be able to,

1) Draw the circuit diagram of a single tube fluorescent lamp

2) State the function of each component in the circuit3) State probable causes for different problems in the circuit malfunctioning

Aim: To study the working principle, assemble, connect and check the fluorescent tube

light.

Tools Required:

1) Line Tester


1) Fluorescent Tube Light 20 W

2) Tube light fitting

3) Ballast

4) Starter

5) Connecting wires

Types of lamps:


90/112



Construction:

The fluorescent tube light consists, a sealed glass tube. The tube contains very

small amount of Mercury mixed with an inert gas, typically Argon, kept under very

low pressure.

The tube also contains a Phosphor powder, coated along the inside of the glass.


91/112



The tube has two electrodes, one at each end, which are connected to the electrical

supply through bi-pin plugs at both ends of the tube.

Ballast/ Choke: Starter:

Circuit diagram:

Starter

CapacitorCathode

Ballast/

Choke

Switch

240V, AC

Supply

Bi-PinPlug

Cathode

Bi-PinPlug


92/112



Features of Fluorescent Tube Light:

require a ballast

have a range of color temperatures and color rendering capabilities have low surface brightness compared to point sources

have a cooler operation are more efficacious compared to incandescent ambient temperatures and convection currents can affect light output and life all fixtures installed indoors must use a Class P ballast that disconnects the ballast in

the event it begins to overheat; high ballast operating temperatures can shorten

ballast life

have options for starting methods and lamp current loadings require compatibility with ballast low temperatures can affect starting unless a "cold weather" ballast is specified

Working of the Fluorescent Tube Light Circuit:

The electrical circuit is connected to an alternating current (AC) supply of 240V, 50 Hz.

When the switch is turned ON, the path of least resistance is through the bypass

circuit, and across the starter switch. In this circuit, the current passes through the

electrodes on both ends of the tube. These electrodes are simple filaments, like you

would find in an incandescent light bulb. When the current runs through the bypass

circuit, electricity heats up the filaments. This boils off electrons from the metal

surface, sending them into the gas tube, ionizing the gas.


93/112



At the same time, the electrical current sets off an interesting sequence of events in

the starter switch. The conventional starter switch is a small discharge bulb,

containing neon or some other gas. The bulb has two electrodes positioned right

next to each other. When electricity is initially passed through the bypass circuit, an

electrical arc (essentially, a flow of charged particles) jumps between these

electrodes to make a connection. This arc lights the bulb in the same way a larger

arc lights a fluorescent bulb

One of the electrodes is a bimetallic strip that bends when it is heated. The small

amount of heat from the lit bulb bends the bimetallic strip so it makes contact with

the other electrode. With the two electrodes touching each other, the current

doesn't need to jump as an arc anymore. Consequently, there are no charged

particles flowing through the gas, and the light goes out. Without the heat from the

light, the bimetallic strip cools, bending away from the other electrode. This opens

the circuit.

By the time this happens, the filaments have already ionized the gas in the

fluorescent tube, creating an electrically conductive medium. The tube just needs avoltage kick across the electrodes to establish an electrical arc. This kick is provided

by the lamp's ballast , a special sort of transformer wired into the circuit.


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When the current flows through the bypass circuit, it establishes a mag

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Electrical Skills Lab Manual

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