fet first

electrical systems and construction Revised edition NQF Level 2

Student’s Book

Jowaheer Consulting and Technologies

FET FIRST Electrical Systems and Construction NQF Level 2 Student’s Book © Jowaheer Consulting and Technologies, 2012 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, photocopying, recording, or otherwise, without the prior written permission of the copyright holder or in accordance with the provisions of the Copyright Act, 1978 [as amended]. Any person who does any unauthorised act in relation to this publication may be liable for criminal prosecution and civil claims for damages. First published 2012 by Troupant Publishers [Pty] Ltd P.O. Box 4532 Northcliff 2115 Distributed by Macmillan South Africa [Pty] Ltd Typesetting by The Purple Turtle Publishing Services Cover Design by Brandtalk ISBN: 978-1-430800-38-5 It is illegal to photocopy any page of this book without written permission from the publishers. While every effort has been made to ensure the information published in this work is accurate, the authors, editors, publishers and printers take no responsibility for any loss or damage suffered by any person as a result of reliance upon the information contained therein. The publishers respectfully advise readers to obtain professional advice concerning the content. To order any of these books contact Macmillan Customer Services at: Tel: (011) 731 3300 Fax: (011) 731 3535 email: [email protected]

Contents Topic 1: Basic electrical circuits and systems................................................... 1 Module 1: Basic electrical installations and testing............................................................................ 2 Unit 1.1: Electrical circuit diagrams and related symbols.................................................... 3 Unit 1.2: Planning according to accepted standards.......................................................... 13 Unit 1.3: Work practices in an electrical environment........................................................ 14 Unit 1.4: Electrical installations according to relevant SABS regulations............................... 24 Unit 1.5: Testing a domestic electrical installation............................................................. 39 Summary......................................................................................................................... 55 Summative assessment..................................................................................................... 57

Topic 2: Low-voltage cables and wireways....................................................... 59 Module 2: Joining low-voltage cables............................................................................................... 60 Unit 2.1: Safety considerations when joining conductors.................................................... 61 Unit 2.2: Regulations relating to joining........................................................................... 64 Unit 2.3: Types of joints and joining methods................................................................... 66 Unit 2.4: Armoured cables and glands............................................................................. 74 Unit 2.5: Using a joining kit to join an unarmoured cable.................................................. 79 Summary......................................................................................................................... 81 Summative assessment..................................................................................................... 82 Module 3: The purpose and design of wireways................................................................................. 83 Unit 3.1: Wireways....................................................................................................... 83 Unit 3.2: Installing electrical wireways: conduits............................................................... 86 Unit 3.3: Installing wireways: trunking and trays............................................................... 95 Unit 3.4: Teamwork...................................................................................................... 101 Summary......................................................................................................................... 104 Summative assessment..................................................................................................... 104

Topic 3: Electrical machines........................................................................... 106 Module 4: Inspecting and cleaning an electrical machine.................................................................... 107 Unit 4.1: Statutory requirements when working on electrical machinery.............................. 108 Unit 4.2: Types of electrical machine and connection diagram............................................ 111 Unit 4.3: Permit to Work systems and lockout procedures.................................................. 131 Unit 4.4: Inspecting, cleaning and labelling electrical machines.......................................... 137 Summary......................................................................................................................... 152 Summative assessment..................................................................................................... 154

Topic 4: Fault-finding and testing.................................................................... 156 Module 5: Fault-finding and testing of electrical components............................................................... 157 Unit 5.1: Fault-finding and testing of electrical components................................................... 158 Summary......................................................................................................................... 170 Summative assessment..................................................................................................... 171

Contents Topic 5: Protection and measuring instruments................................................. 172 Module 6: Installing and replacing metering units or measuring instruments......................................... 173 Unit 6.1: Introduction to electrical metering units or measuring instruments......................... 174 Unit 6.2: Planning the installation................................................................................... 185 Unit 6.3: Installing a metering unit or measuring instrument.............................................. 194 Summary......................................................................................................................... 206 Summative assessment..................................................................................................... 207 Module 7: Completing the installation and/or replacement of a metering unit or measuring instrument on a panel...................................................................................................................... 209 Unit 7.1: Completing the installation and/or replacement of a metering unit or measuring instrument on a panel...................................................................................... 210 Summary......................................................................................................................... 214 Summative assessment..................................................................................................... 216

Topic 6: Renewable energy............................................................................. 218 Module 8: Photovoltaic systems....................................................................................................... 219 Unit 8.1: Photovoltaic systems....................................................................................... 219 Summary......................................................................................................................... 229 Summative assessment..................................................................................................... 230 Module 9: Basic renewable energy circuit diagram............................................................................. 232 Unit 9.1: Worksite procedures........................................................................................ 232 Unit 9.2: Symbols and circuit diagrams........................................................................... 236 Summary......................................................................................................................... 241 Summative assessment..................................................................................................... 242

POE Guideline................................................................................................ 244 Glossary........................................................................................................ 249

Topic 1

Basic electrical circuits and systems

Module 1 Basic electrical installations and testing Overview Whether it is a construction site, minor household repairs or even a simulated environment in a training workshop, working with electricity is dangerous. Your own safety and that of your co-workers is therefore of the utmost importance. Although electricity is a modern convenience that many of us take for granted, there are dangers associated with it. In this module you are going to learn how to test, install or replace basic electrical circuits and systems, including making domestic wiring installations safe for use. Wiring and commissioning a single-phase installation may seem like a simple task, but you will need to know and apply all the statutory regulations and other legal requirements relating to electrical installations. Ensuring that electrical installations function and meet requirements, that work is done to an acceptable standard, and that the worksite is left neat and tidy on completion is also part of your task. Finally, you will need to practise what you learn, as practice makes perfect. When you have completed this module, you will be able to: • Read and interpret electrical circuit diagrams and related symbols correctly. • Plan and prepare for an electrical installation job in accordance with job requirements and workplace standards, and policies and procedures. • Perform an electrical installation according to relevant SABS standards on domestic installations. • Test the installation according to relevant SABS standards on domestic installations. • (Faults are simulated and the student does fault-finding and reports on the outcome.) • Make sure that electrical installations function properly and meet job requirements. • Replace and maintain electrical equipment in a domestic dwelling. • Clean the worksite.

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Topic 1 Basic electrical circuits and systems

Think about it Electricity can kill. How can we make sure that electrical installations are safe for use? The only way to do this is to make sure that an installation follows certain rules and regulations. In South Africa, all electrical installations must, by law, comply with the South African National Standards code for electrical installations, also called SANS 10142-1: 2012 or the Code of Practice for the Wiring of Premises. This code provides certain set standards for all electrical procedures. These rules are not at all difficult to understand and apply. However, it is important that you do not just memorise them, but that you think about what they are prescribing and why. You will learn more about these standards in Unit 1.4.

Units in this module Unit 1.1: Electrical circuit diagrams and related symbols Unit 1.2: Planning according to accepted standards Unit 1.3: Work practices in an electrical environment Unit 1.4: Electrical installations according to relevant SABS regulations Unit 1.5: Testing a domestic electrical installation.

Unit 1.1 Electrical circuit diagrams and related symbols Introduction Before starting any task, an electrician must study and understand various electrical plans, drawings and circuit diagrams for an installation to form a clear picture of what the actual completed electrical installation will look like. Diagrams are valuable tools for field staff. Electricians use diagrams to identify the connections of components and to work out accurately the quantities of materials needed. In this unit you are going to learn the important skill of being able to read and interpret circuit diagrams and related symbols correctly.

Electrical wiring symbols A drawing of components in a circuit makes it easier to understand how the circuit components are connected. Wiring and circuit diagrams use special symbols recognised by everyone who uses the drawings. The electrical symbols on the drawings show how components such as lights, switches, circuit-breakers and other electrical components are connected. Electrical symbols not only show us where something is to be installed, but they also help electricians to find out why a circuit does not work correctly.

Words & terms alternating current (AC): an electric current that reverses direction at regular intervals circuit breaker: a type of switch with a pre-set current limit that is used to protect a circuit from electrical overload direct current (DC): an electric current flowing in one direction only fuse: a protection device that destroys itself, or ‘blows’, and breaks the circuit if the current exceeds the rating of the fuse

Module 1 Basic electrical installations and testing

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Table 1.1 shows the most common electrical wiring symbols. These symbols are used to represent wiring, components and apparatus in circuit diagrams. It is therefore important that you learn the various symbols and what they mean.

?

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Did you know?

If the circuit-breaker trips, it can be reset by pushing a button or flipping a switch. However, the reason for the overload must be investigated because it may indicate a fault in the circuit.

OR X

Table 1.1 Electrical wiring symbols

Electrical diagrams Electrical diagrams may represent anything from a simple single-line drawing to a complex power control circuit. They are usually drawn using different symbols for electrical devices. The three most common types of diagram encountered in the field are: • circuit diagrams • wiring diagrams • block diagrams.

Circuit diagrams A circuit diagram uses symbols to represent all the circuit components and shows how the components are connected in a circuit. It is drawn in a 4

Topic 1 Basic electrical circuits and systems

Words & terms circuit diagram: uses electrical symbols to represent all circuit components and shows how they are connected

simple, clear way as shown in Fig. 1.1. The shape of the diagram does not represent the physical layout of the circuit.

Wiring diagrams A wiring diagram shows how the components are to be wired and where the connections must be made. Unlike a circuit diagram, the physical layout in a wiring diagram is taken into consideration. The components and connections are shown as pictures of what is found in the actual wiring and are often drawn to look like what they represent. They are shown on the drawing in the positions they will occupy as illustrated in Fig. 1.2. The main purpose is to give information.

Fig. 1.1 A simple circuit diagram

Words & terms wiring diagram: shows how the components are to be wired, where the connections must be made and takes the physical layout into consideration block diagram: sometimes referred to as a ‘line diagram’; uses either square or rectangular blocks to represent plant or equipment

Fig. 1.2 A wiring diagram

Block diagrams A block diagram is sometimes referred to as a ‘line diagram’. It uses either square or rectangular blocks to represent plant or equipment. Lines are drawn to show interconnections between blocks but do not represent actual wiring. A block diagram is shown in Fig. 1.3.

Guidelines for drawing circuit diagrams

Fig. 1.3 A block diagram

A circuit diagram should be drawn in such a way that it allows the reader to identify its purpose. When you draw circuit diagrams you should: • use the correct symbols. • use a suitable symbol orientation. • pay attention to the arrangement of symbols on the diagram. • pay attention to the routing of interconnections. • make sure your drawing is neat and tidy. Input to output is always drawn from left to right or from top to bottom. For example, if a Fig. 1.4 The correct way of drawing input to output transformer is used to step down voltage to a circuit, the input is drawn on the left-hand side as shown in Fig. 1.4. Module 1 Basic electrical installations and testing

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Relays and switches in circuit diagrams are normally shown in their nonoperating mode, in other words when no current is flowing. A line representing a conductor should not change direction at a point where it crosses other lines. Lines from a symbol should continue for a short distance before they change direction, cross another line or connect to another symbol.

assessment activity 1.1 Work in groups of five 1. List the three most common types of diagram that you will come across in the field and briefly describe each one with an example. 2. Your lecturer will supply you with an electrical drawing. Identify the symbols and abbreviations on the drawing and exchange your answers with another group. 3. Sketch the symbols of the following: a) A fuse b) A single-pole switch c) A lamp d) A resistor

circuit diagrams of electrical subcircuits subcircuits of luminaires The accessories used to wire up lighting circuits include cables, screw connectors, lamp-holders and switches. All circuits must include a protection device such as a circuit-breaker and the switch must be placed on the live side of the circuit. Never install a single-pole switch in the neutral conductor of the circuit. The following circuit diagrams show the correct way to wire subcircuits: • One luminaire controlled from one switch (see Fig. 1.5) • Two luminaires controlled from one switch (see Fig. 1.6) • Two luminaires controlled from own switches (see Fig. 1.7) • One luminaire controlled from two switches (see Fig. 1.8) • Intermediate switching (see Fig. 1.9).

one luminaire controlled from one switch Circuit breaker

Bulb

L Switch

N

Fig. 1.5 One luminaire controlled from one switch

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Topic 1 Basic electrical circuits and systems

note Earthing in the luminaire circuits has been removed for clarity.

Words & terms luminaire: a complete lighting fixture consisting of a lamp and ballast together with the parts designed to distribute the light, position and protect the lamp, and connect them to the power supply ballast: a device for star ting and regulating fluorescent and highintensity discharge lamps

Two luminaires controlled from one switch circuit breaker L switch

Bulbs

N

Fig. 1.6 Two luminaires controlled from one switch

Two luminaires controlled from own switches circuit breaker L switch

Bulbs

N

Fig. 1.7 Two luminaires controlled from own switches

One luminaire controlled from two switches It is sometimes necessary to control a light independently from two switches. This may be necessary for staircases and long passages. Fig. 1.8 shows the circuit diagram. Two-way switches are necessary for this type of configuration. The live wire is connected to terminal A of the first two-way switch. The movement of the switch makes contact from the common terminal A to either terminal B or C. Another twoway switch is positioned further away from the first one. Two strapping wires are run from B to B1 and C to C1. The diagram shows the circuit in an open position. If either switch is moved the circuit is made and the lamp therefore lights. When the lamp is on, moving either of the switches breaks the circuit. C1

C L

A

B

Bulb A1

B1

two-way switches N

Fig. 1.8 One luminaire controlled from two switches

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intermediate switching If more than two switch locations are necessary, such as in long passages and multiple staircases, then intermediate switches must be used between the two-way switches. The function of the intermediate switches is to crossconnect the wires between the two-way switches as shown in Fig. 1.9. Bulb circuit breaker

Fig. 1.9 One luminaire control from three different positions (intermediate switching)

in the workplace It is common practice to use different colours when wiring light switches so that you can differentiate between the incoming wire and the outgoing wire.

a low-voltage transformer circuit Low-voltage lamps are becoming increasingly popular as display lighting. These lamps are available as 6 V, 12 V or 24 V but 12 V is the most popular. Fig. 1.10 shows a 12 V low-voltage lamp. However, a step-down transformer must be used to operate low-voltage lamps. For example, a 230/12 V, 50 VA transformer will give 12 V from a 230 V input and can supply current for a 50 W lamp load. Fig. 1.11 shows the connection diagram for a low-voltage halogen lamp with a step-down transformer. Fig. 1.10 A 12 V low-voltage halogen lamp 230 V / input

230 V / 12 V 50 VA transformer

12 V output

note Low-voltage transformers are also used in bell circuits. Fig. 1.11 The connection diagram for a low-voltage halogen lamp with a step-down transformer

a socket outlet circuit A socket outlet must be controlled by means of a switch in each live conductor. The socket outlet is connected in such a way that each socket outlet is supplied from the previous one (see Fig. 1.12 for an example). Different circuit-breakers control various sections based on the size of the installation. 8

Topic 1 Basic electrical circuits and systems

Circuit breaker

Words & terms Socket outlet

Switch

Fig. 1.12 Two sockets supplied from one circuit-breaker

A geyser circuit Fig. 1.13 shows a geyser circuit, including the isolator and ripple relay. A double-pole switch must be installed within arm’s reach of the geyser. Ripple relay

Double-pole isolator

Thermostat

socket: a device with female contacts that is installed with the fixed wiring and that is intended to receive a plug isolator: a switch that isolates a circuit by disconnecting both the live and neutral lines isolate: to make sure that a circuit cannot become live while it is out of service for maintenance ripple relay: an electrical switch that is remotely controlled by the power supplier which introduces a coded signal into the electrical network

Element

L

N

Geyser

E

Fig. 1.13 A geyser circuit including isolator and ripple relay

A stove circuit Fig. 1.14 shows a single-phase stove circuit with an isolator. Note that L1, L2 and L3 are joined or bridged together.

L1 L2

Bridged together

L3 N E

Back of stove

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??

Did you know?

Ripple relays are used to switch the load off and on from a distance (remotely). For example, in many towns ripple relays are installed in households to allow the supplier to switch the geyser on and off at set times to cut electricity usage, especially during peak hours.

Fig. 1.14 A single-phase stove circuit including isolator Module 1 Basic electrical installations and testing

9

in the workplace The internal wiring of a stove is often subject to high temperatures so when rewiring stoves, use heat-resistant wiring.

Wiring of a distribution board Fig. 1.15 shows the wiring of a distribution board where all the subcircuits are on the earth leakage unit. As can be seen in the diagram, different sizes of circuit-breakers are used for protection.

Words & terms Fig. 1.15 The wiring of a distribution board

recommended conductor sizes for domestic installations Table 1.2 shows some of the recommended conductor sizes for domestic installations. electrical subcircuit

size of wire

Bell circuit

1 mm2

Light circuit

1,5 mm2

Socket outlet

2,5 mm2

Geyser

4 mm2

Stove

6/8 mm2

Distribution board wiring

10 mm2

Supply from meter to distribution board

16 mm2

Table 1.2 Recommended conductor sizes for domestic installations

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Topic 1 Basic electrical circuits and systems

distribution board: an enclosure that contains electrical equipment for the distribution or control of electrical power from one or more incoming circuits to one or more outgoing circuits

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did you know?

The advantage of miniature circuit-breakers (MCBs) is that if they trip, they can be reset. They also offer a more precise tripping value. A circuit-breaker has a line side and a load side. The incoming power line is always connected to the line side and the outgoing wires to the load side.

Preparing the parts list It is important for the electrician to prepare a parts list of materials that will be required for a specific installation. These materials fall into two main categories, namely numbered parts and measured parts.

Numbered parts These are materials that can be counted, for example circuit-breakers, socket outlets and lever switches. The most logical way to count these items is to draw up a checklist with rows and columns as shown in Table 1.3. Customer name:

Customer address:

Name of chief electrician doing installation:

Contact numbers:

Item No

Description

Quantity

1

Single lever switches

8

3

2

Two way switches

2

3

3

...

...

4

....

...

5

...

...

Yes

No

Table 1.3 A checklist for numbered parts

Measured parts These are materials that need to be charged per length required, for example cable and PVC (polyvinyl chloride) trunking or tubing. These materials must be measured accurately. It is common practice to add an extra amount for termination of the cable at either end. The electrician writes the list of materials (both the numbered and measured parts) on a requisition, order or quotation form and hands it to the customer or the store, depending on company policy. An example of a materials requisition form is shown in Table 1.4.

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materials requisition form date:

installation to be completed on:

customer name:

customer address:

name of chief electrician doing installation:

contact numbers:

account no:

erf no:

reference

description

Quantity

Distribution board

20-way flush mount

1

Earth leakage 63 A, 30 mA (CBI) with overload

1

…

…

…

...

...

Table 1.4 A materials requisition form

assessment activity 1.2 Work on your own 1. Neatly draw the following subcircuit diagrams which must be labelled and include protection devices: a) Two luminaire circuits supplied from one circuit-breaker b) A geyser circuit including the isolator and ripple relay c) A single-phase stove including the isolator. 2. Are the following statements true or false? If a statement is false, correct it. a) A switch is connected on the neutral side of the circuit. b) A double-pole isolator disconnects both the live and neutral wires. c) An isolator switch is installed near the geyser, usually within arm’s reach, for safety during maintenance. d) It is usual to use a 2,5 mm2 conductor for a stove connection. e) Low-voltage transformers are also used in stove circuits. 3. Refer to Fig. 1.16 and identify the symbols labelled A, B, C and D. 4. What will happen if component C in Fig. 1.16 is removed and replaced with a piece of 2,5 mm2 wire? 5. What will happen if component D in Fig. 1.16 is removed and replaced with a piece of 4 mm2 wire.

Fig. 1.16 A circuit diagram

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Topic 1 Basic electrical circuits and systems

Unit 1.2 Planning according to accepted standards Introduction Proper and effective planning is vital in any electrical work. Planning is the organisational process of creating and maintaining a plan. It is concerned with: • what is to be done • where is it to be done • how it is to be done.

Note A plan should be a realistic view of the expectations.

The term is also used to describe the formal procedures used in such a job, for example creating documents or diagrams, or holding meetings to discuss important issues that need to be addressed, the objectives or goals to be met, and the strategy to be followed. Before you start a project, it is important to plan properly the procedure you will follow, prepare the work area, and select and obtain the right tools for the job. In this unit you are going to learn how to plan a job according to accepted standards.

Why do we need to plan? It is important to prepare a plan, keeping in mind the fundamental requirements of the project (Fig. 1.17). The five main reasons for planning are to: • provide direction • minimise waste • set the standards to facilitate control • identify and commit resources to achieve goals • decide which tasks must be done to achieve these goals. A plan plays an important role to help you avoid mistakes. Preparing a satisfactory plan of the project is therefore essential. The planning process lets us understand more clearly what we want to achieve, and how and when we can do it.

Factors relating to the completion of a task in accordance with acceptable standards

Fig. 1.17 Planning involves the setting of goals

Think about it Preparing a comprehensive plan will not guarantee success, but not having a proper plan will almost certainly mean total failure. What are your views?

When planning, it is necessary to consider certain factors to make sure that the task is completed in accordance with acceptable standards. When you are assigned a task, take the following factors into consideration: • by what date must the task be completed? • obtain as much information as possible about the task to be done. • obtain the necessary plans, documents and diagrams. • when must the task start? • how many workers will be available? • what tools and equipment will be needed? Module 1 Basic electrical installations and testing

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• • • •

what materials must be ordered? what documentation is needed according to the job instructions? inform all the relevant parties affected. submit appropriate requests to the supply authority, for example an application for an electricity connection? • what will happen in the case of unforeseen circumstances, such as a taxi strike or if materials are not available?

think about it A well-prepared and designed plan shows that the person knows what he or she is doing and that they have thought through the process before starting the job. This is in contrast to someone who does not ‘waste’ any time planning and preparing, but instead jumps right in and strips everything in the hope of finding the fault by a stroke of good luck. Which type of person do you think will inspire the most confidence in the client?

assessment activity 1.3 Work in pairs 1. List five main reasons for planning. 2. List at least ten factors for making sure that a task is completed within acceptable standards. 3. Create a checklist for the completion of a task in accordance with acceptable standards.

unit 1.3 Work practices in an electrical environment introduction It is important to have a good understanding of sound work practices and adhering to them. Working safely in an electrical environment is important for your own well-being and for the well-being of others around you. Electricity can kill and injure people. To overcome these threats, planned and proactive work practices are vital. This unit introduces you to essential work practices and will also help you to appreciate some of the potential electrical hazards that exist in the workplace.

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Topic 1 Basic electrical circuits and systems

Words & terms electrical hazard: a dangerous condition in which an accidental or unintentional contact or equipment failure can result in shock, arc flash burn or thermal burn

in the workplace If you find any hazards during your inspection of the work area, make a note of them in writing and tell your supervisor. If it is something small, such as some tools lying around, then you can correct the situation yourself. However, the supervisor must still be informed so that action can be taken to prevent it from happening again. If it is a faulty tool or wire connection, then the proper procedure must be followed. Work must not start before the supervisor has taken the correct action and the danger has been removed. In the workshop, if you regularly inspect your workbench, keep it clean and inspect your tools every time before you use them, then you will be compliant with the rules and regulations.

Hazards Electrocution remains the leading cause of electrical injury. Understanding and recognising the hazards of electricity is the key to preventing injury. Electricians must be trained to identify and avoid the hazards involved in working with electricity.

What is a hazard? The Occupational Health and Safety Act No. 85 of 1993 defines a hazard as a source of danger such as the risk of being electrocuted, or exposure to excessive heat and noise. No one wants to be injured or become sick as a result of risky or hazardous working conditions. Although some hazards are fairly obvious and easy to identify, others are not, and you should therefore take all necessary safety precautions to identify hazards in the workplace and be aware of hazardous areas (Fig. 1.18).

Fig. 1.18 A sign indicating a hazardous area

Hazard management For any system to work properly people must be trained so that they know what to do, when to do it, how to do it and why. Obviously no one wants to be injured or become sick as a result of their working conditions. If everybody is aware of possible hazards and knows how these can affect them, as well as what equipment is available to protect them from injury, hazards can be effectively avoided. Workplace inspections should focus on identifying hazardous conditions, unsafe work practices and violations of standards. These inspections are also used to follow up on accident reports. As a good work practice, time should be set aside for general health and safety procedures which could include the following: • report all hazards, and know how and to whom they should be reported. • where possible, make all potential hazards safe. • report all incidents immediately. • follow all health and safety instructions regarding making equipment safe, and also use all required personal protective equipment. • maintain all personal protective equipment and replace if defective.

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Hazards can arise from: • the work environment • the use of machinery and substances • poor work design • inappropriate systems and procedures.

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Example of a hazard assessment You need to conduct a review of your employer’s operations from a safety and health perspective. During the walk-through, assess various health and safety issues, including but not only, the following: • the building, floors and stairs for physical hazards • the functionality and placement of fire exits (see Fig. 1.19), fire protection equipment and first aid signs (see Fig. 1.20) • the space layout in aisles and between machines • electrical and mechanical hazards • the control of worker exposure to occupational hazards, including toxic and corrosive substances, and especially air contaminants • the availability and functioning of all necessary personal protective equipment and whether employees know how to use and care for the equipment • workers’ exposure to noise, vibration, lighting or other environmental factors • the use of adequate safety signage (see Fig. 1.21) • work practices, including general housekeeping • the use and maintenance of hand and portable power tools.

Fig. 1.19 Fire exit

Fig. 1.20 First aid sign

Did you know?

Hazards are classified into five broad areas, namely physical, mechanical and/ or electrical, chemical, biological and psychological.

Think about it You can help prevent workplace injuries and illnesses by looking at your workplace operations, establishing proper job procedures, and ensuring that all employees are trained properly. Management must demonstrate its commitment to safety and health, and correct any uncontrolled hazards that have been identified. If management fails to do this, it will lose credibility and employees may hesitate to report dangerous conditions. What is your viewpoint?

Fig. 1.21 Safety signs

The dangers of electricity Electricity has become such a basic part of our society that it is often taken for granted. Yet electricity remains a dangerous hazard for people (Fig. 1.22). Because the human body can conduct electricity, people can be shocked, burned or killed as a result of electrocution.

Types of injury associated with electricity There are four main types of electrical injury: • electrocution • electric shock • burns • falls. 16

Topic 1 Basic electrical circuits and systems

Fig. 1.22 Danger sign

Causes of electrical accidents

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Some common causes of electrical accidents are the following: • inattention and carelessness • inadequate power-line clearance • poor housekeeping • taking chances • overloading of electrical circuits • careless use of mobile scaffolding • failure to adhere to sound work practices (see Fig. 1.23) • bypassing or ignoring safety procedures • lack of knowledge • fatigue • faulty or unguarded machinery (see Fig. 1.24)

?

??

Effect on body

1

First sensation noticeable

2,5

Palms start to tingle

7,5

A fatal electric shock is referred to as electrocution.

Did you know?

Current (mA)

5

↑ Safe zone

Cramping starts Hands stiffen; still possible to let go

10–15

Cramps increase; difficult to let go

25–30

Severe cramping in chest area; limit of safe current

30–50

Did you know?

50–60

Danger zone

60–75

↓

Blood pressure increases; irregular heartbeat Difficulty breathing; loss of consciousness (fainting) Heart failure and death

Fig. 1.23 Not adhering to sound work practices

Fig. 1.24 Unguarded machinery

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Electrical safeguards There are several safeguards typically used to reduce the possibility of electrical accidents, for example the use of: • circuit-breakers • direct earthing • isolating transformers • double-insulated appliances • earth leakage circuit-breakers.

?

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Did you know?

The international symbol for double insulation is a square within a square. See Fig. 1.25 for an example.

Safety precautions when working with or near electricity • Do not use power tools with defective cords (see Fig. 1.26). • Use only cords or equipment rated for the level of amperage or wattage that you are using. • Always use wooden ladders or other non-conductive materials when working with or near electricity or power lines. • Remember that the risk of electric shock is greater in areas which are wet or damp. • Know where the distribution board is in case of an emergency. • Label all circuit-breakers so that it is easy to identify which circuits they protect. • Make sure that the lockout isolator is in the OFF position with a tag on it to inform others (see Fig. 1.27). • Do not use outlets or cords that have exposed wiring. • Do not block access to circuit-breakers. • Do not touch a person or electrical apparatus if there is an electrical accident. Always disconnect the current first and then attend to the accident.

Fig. 1.25 The symbol for double insulation An appliance labelled with this symbol has additional insulation between any exposed metal parts. The usual insulation of the current-carrying parts is therefore also insulated, hence the term ‘double insulation’.

Words & terms insulation: a material that does not conduct electricity and which is used to isolate current-carr ying wires or components from other metal parts lockout: the placement of a lockout device, for example a padlock, to isolate certain circuits or devices from the power source

Fig. 1.26 Defective power cords Fig. 1.27 A lockout and tagout devices

Think about it Locking out equipment is the only sure way to prevent serious or fatal injuries that could result from the unexpected start-up of machines. A tagout device, on the other hand, is a prominent warning sign, such as an easily visible tag, securely attached to an energy-isolating device. When you find a tagged power box, make no attempt to restore the power until the repairs have been made and the tag has been removed by the person who placed it there. What would you do if you could not find the person who put the lock and tag on the device?

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Topic 1 Basic electrical circuits and systems

Manual handling Many accidents occur due to manual handling of loads. Sprains and strains, particularly of the back, are quite common. In many cases, these injuries result in a temporary absence from work, but they can sometimes be serious enough to lead to permanent disablement. When you lift loads, use the correct lifting procedures to prevent back injuries. Fig. 1.28 shows how you can do this.

7

3

Words & terms Manual handling: the transpor ting or supporting of loads by hand or by bodily force, including lifting, putting down, pushing, pulling and carr ying a load

Fig. 1.28 Lifting techniques

Safe work practices must be used for manual operations. Staff should be well trained and supervisors must make sure that correct procedures are followed and the necessary personal protective equipment is worn at all times. Some safe practices to follow when lifting loads are the following: • do not lift a load manually if at all possible. Rather use mechanical (see Fig. 1.29) or electrical means. • use trolleys. • plan properly so that any obstacles can be eliminated. • lift and lower gently. • use gloves to avoid injury to hands. • use a safety sign to remind workers to lift correctly (see Fig. 1.30).

Fig. 1.29 Using a mechanical aid to move a load

Fig. 1.30 ‘Lift correctly’ signs Module 1 Basic electrical installations and testing

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assessment activity 1.4 Work on your own 1. What do you understand by the word ‘hazard’? 2. What causes hazards? 3. List at least five common causes of electrical accidents. 4. List at least ten safety precautions to follow when working with or near electricity. 5. List some safe practices to follow when lifting loads.

Housekeeping An uncluttered workplace is fundamental to any company’s safety programme. In addition to cleanliness, housekeeping must include other factors such as orderliness and proper arrangement of materials. When we think of housekeeping it is useful to think of the common phrase, ‘A place for everything and everything in its place’. This means that tools and equipment are not left lying around and that they are properly stored in the correct place. A clean, well-ordered working area and good housekeeping improve a company’s image and reflect a wellrun business. An orderly workplace will impress anyone who enters it. Remember, first impressions last! It is important to know the benefits of good housekeeping. Let's review why we need good housekeeping and some common signs of poor housekeeping.

Why good housekeeping? Sloppy working conditions lead to a lack of pride in your work and also create hazards that can lead eventually to injury or accidents. Poor housekeeping thus creates hazards for all employees.

common signs of poor housekeeping There are many signs of poor housekeeping. The following are some examples: • excessive materials or waste in the work area • overcrowded passageways and aisles • tools and materials left on machines or walkways • dusty, dirty floors and wet work surfaces • overflowing waste containers • untidy or dangerous storage of materials, for example materials packed in corners or on overcrowded shelves • cluttered and poorly arranged work areas • items stored overhead in such a way that they could easily fall • objects stored on ladders or stairs • storage of items that are obsolete (no longer needed).

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For a housekeeping programme to be effective, everyone must play their part. Do not expect maintenance personnel, a labourer or a co-worker to clean up your area. However, management should provide brooms, mops and cleaning materials.

Think about it Housekeeping is more than just sweeping the floor and wiping dust off machines and equipment. Cleanliness is only one part of housekeeping. The most critical and most overlooked part of housekeeping is order. A work area is in order when there are no unnecessary objects in the area and when all necessary items are in their proper places. A daily conscious effort by everyone working in the area is necessary to maintain order. What do you think?

Testing tools and equipment In general, tools and equipment that are poorly maintained, inappropriately used or not fit for purpose can cause injuries. With electrical work, there is also the added risk of electric shock. The tools and equipment used by electricians often have special design characteristics. For example, many are insulated as a safety measure. However, it is important that you inspect and maintain the tools and equipment regularly. Dangers arise from faulty tools and equipment, for example the insulating material may hide a mechanical defect that could cause an open circuit in the lead of a testing device. Users should be competent in the use of tools and equipment. This means: • being able to use the device safely and in the manner for which it was intended • being able to determine, by inspection, that the device is safe for use, in other words, the device is not damaged and is fit for purpose • understanding the limitations of the equipment, for example when testing to prove an AC circuit is de-energised whether the testing device indicates the presence of hazardous levels of direct current (DC) • being aware of the electrical safety implications for other people near you when the device is being used • knowing what, the interest of electrical safety, when you get an incorrect result. When selecting tools and equipment, keep the following guidelines in mind: • the device must be fit for purpose. • you must test your equipment and test instruments at least every six months and recalibrate once a year to check they are in proper working order. • repairs and maintenance should meet appropriate standards and the manufacturer’s specifications. Module 1 Basic electrical installations and testing

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• inspect the device and perform functional checks immediately before and after use to confirm that the device is operating correctly (see Fig. 1.31). • the work practices employed during use should be in line with documented procedures. These documented procedures should include the manufacturer’s instructions and recommendations. • the function, range and class of accuracy of the device should be appropriate to both the job at hand and the general working conditions. • the combination of leads and instruments used should be capable of withstanding the impulse voltages and fault current levels that may be experienced at the particular location.

Fig. 1.31 Checking for voltage before working

in the workplace If you notice a problem during inspection that makes the tool unsafe for use or discover that some part of the tool does not work, then it is important that you do not use it, but remove it and mark it for repairs. The marking procedure differs from workshop to workshop. Some companies use labels attached with strings, while others use stickers that you can stick onto the tool. Find out from the supervisor which procedure is followed at your place of work. What is important is that you must identify the problem as far as possible and note it on the label you put on the tool. After you have identified the fault and written it on the tool, return the tool to the store. Make sure the attendant signs off on it so that it is not longer issued in your name!

Warning signs and notices Appropriate warning signs and notices should be openly displayed in the workplace (see Fig. 1.32). It is important to learn the different types of sign and what they mean. Some examples are: • these signs must be fixed securely where they can be seen clearly (and not obscured in any way) at all entrances to hazardous areas and in all workplaces. • if the warning or instruction applies during the hours of darkness, the signs must be placed or illuminated in such a way that they can be easily read. • warnings of hazards must be displayed near machinery that could cause injury to operators if improperly used, for example abrasive wheels. A reminder notice should also be displayed, for example ‘Goggles must be worn’. • signs and notices should conform to recognised national standards.

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Fig. 1.32 Different safety signs

tools Tools for the electrical environment must be insulated. For example, Fig. 1.33 shows insulated screwdrivers. The following criteria can be used when selecting tools: • use the correct tool for the job. • use the tool properly and within its limitations. • always store tools safely after use. • always buy good-quality tools and keep them in good condition. it's more than following work practices To be truly safe, keep to work practices during a project or task and make safe work habits second nature. Look out for everyone. Take responsibility for noticing, reporting and correcting hazards. stay alert Many electrical injuries could be prevented if people were alert to hazards. Stay aware by keeping focused on your job and do not let emotions such as anger and frustration get in the way.

Fig. 1.33 An insulated screwdriver set

avoid unsafe shortcuts It may take longer to keep your area clean and dry, or inspect cords for wear, but it is worth a few minutes to prevent shock or fire. Shields, barriers, insulation and earth leakage devices protect you so do not modify them just to get a job done faster. use personal protection equipment Personal protective equipment is your line of defence against shock and electrical burns. Keep boots, gloves and other gear in good condition at all times. learn to say ‘no’ If the task assigned to you will be a threat to safety, say ‘no’. Warning notices and barriers Check that warning notices and barriers are fitted and installed correctly. clean up Make sure that when you have completed the project or task, you remove equipment and material from the workplace and store it safely as laid down in company policy. Clean up the work area, throw away rubbish and return any unused material to the main stores.

assessment activity 1.5 Work in groups of five 1. There are many signs of poor housekeeping in the workplace. Do a check in your workshop and suggest ways to overcome the problems. 2. What guidelines should you follow when selecting tools and equipment? 3. What method will you use to test for isolation?

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unit 1.4 electrical installations according to relevant saBs regulations introduction Electrical installations in South Africa must conform to the South African National Standards Code SANS 10142-1 : 2012, also called the Code of Practice for the Wiring of Premises or simply the Wiring Code. This code is published by Standards South Africa, a division of the South African Bureau of Standards (SABS). The code sets out specific requirements for the wiring of premises. Most of these rules and regulations involve common-sense ideas, such as using only high-quality materials that will not fail under normal use and conditions. In this unit you will explore some of the relevant SABS regulations for domestic installations.

in the workplace We strongly recommend that you have your own personal copy of the SANS 10142-1 : 2012 Wiring Code as you will often need to refer to the rules and regulations in this document.

understanding sans 10142 The aim of SANS 10142-1 is to make sure that people, animals and property are protected from hazards that can be caused by the operation of an electrical installation under both normal and fault conditions. The various types of protection required by an electrical installation are listed in Table 1.5.

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did you know?

SANS 10142-1 is listed in the Electrical Installation Regulations of the Occupational Health and Safety Act No. 85 of 1993 (OHS Act) as a mandatory (compulsory) safety standard. This means that the rules and regulations in the code have the force of law through the OHS Act.

Words & terms mandatory: containing a command; not having an option to do otherwise frequency: the number of complete waves that pass a point in one second measured in hertz (Hz); in electrical terms, it refers to the number of complete alternations per second of an alternating current (AC); this is 50 cycles per second or 50 Hz in South Africa harmonics: frequencies of a complex wave that are multiples of say 50 Hz such as 100, 150 or 200 Hz

type of protection

explanation

Shock current

Current that passes through the body of a person or an animal that has a value likely to cause injury depending on the frequency, harmonics and duration.

Overcurrent

Current that is greater than the rated current; depending on its magnitude (size) and duration, an overcurrent may or may not be harmful.

Fault current

Current that results from an insulation failure or from the bridging of insulation.

Overvoltage

Voltage that is greater than the supply voltage.

Undervoltage

Voltage that is less than the supply voltage.

Excessive temperature

A temperature greater than: 70 °C in the case of metallic parts 90 °C in the case of non-metallic parts.

Electric arc

The heat and light energy that is released by the electrical breakdown of an electrical insulator such as air and the subsequent electrical discharge through the insulator.

Table 1.5 Potential faults in an electrical installation

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If any of the problems listed in Table 1.5 arise, the protection devices should automatically disconnect the power supply or limit currents and voltage to a safe value. In the case of undervoltage, the protection device should ensure that dangerous situations due to the loss and restoration of power supply or voltage drops do not occur. The designer of an electrical installation should be aware of: • the nature of the power supply • the nature of the demand • the operating environment of each part of the installation.

Think about it Electrical installations must be done in a consistent and uniform way. This is why there are electrical codes such as SANS 10142 to make sure that everyone recognises the correct and incorrect way of doing an electrical repair or installation. If every building was wired according to a random standard, it would be difficult to find and correct faults in a circuit.

Reading and interpreting regulations When you read and interpret regulations, pay special attention to the language that has been used. The same word may have different meanings for different people and each one of us may interpret a regulation in a different way. Pay particular attention to words such as shall and may: • Shall: When this word is used, it means that you must do something in a certain way. If you do not, then you are in violation of the code. • May: When this word is used, it means that you have an option. You can do something the way it is stated or you can do it another way. In other words, the choice is yours. SANS 10142-1 also includes certain provisions that are for information and guidance only. These provisions do not use the word shall and they can be found in the main text, in the notes and in informative annexures. Except in tables, notes are always for information only. There are therefore three types of rule: • Mandatory rules: These use the words shall or shall not. These rules must always be obeyed – if you do not do so, you will be in violation of the code and will therefore be breaking the law. • Permissive rules: These use words such as may, shall be permitted or shall not be required. These rules give you permission to do or not to do something, but you can decide whether to implement the rule or not. • Informational rules: These rules do not prescribe any action; they are for information and guidance only.

Words & terms rated current: the current that an electrical device can carr y, under specified conditions, without resulting in overheating or damage to the device; in the case of conductors, the currentcarr ying capacity is considered to be the rated current

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Did you know?

Any distortions in the voltage or current wave cause harmonics. Harmonics are harmful to electrical distribution systems and to sensitive electronics. They cause transformers to overheat, they overload neutral conductors, have a negative effect on relay settings, metering, capacitors and telephone lines, and cause circuit-breakers to trip for no obvious reason.

Think about it To make sure you interpret the rules and regulations correctly, you must consider each word individually. This requires extra time and more effort, but there is no other way to arrive at the correct interpretation.

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