EE009-Basic Electricity 4-Th-Inst.pdf

7/25/2019 EE009-Basic Electricity 4-Th-Inst.pdf

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SRI LANKA INSTITUTE of ADVANCED TECHNOLOGICAL EDUCATION

Training Unit

Basic Electricity 4Theory

No: EE 009

INDUSTRIETECHNIKINDUSTRIETECHNIK

ELECTRICAL and ELECTRONIC

ENGINEERING

Instructor Manual


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Training Unit

Basic Electricity 4

Theoretical Part

No.: EE 009

Edition: 2008Al l Rights Reserved

Editor: MCE Industrietechnik Linz GmbH & CoEducation and Training Systems, DM-1Lunzerst rasse 64 P.O.Box 36, A 4031 Linz / Aus triaTel. (+ 43 / 732) 6987 3475Fax (+ 43 / 732) 6980 4271Website: www.mcelinz.com


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BASIC ELECTRICITY 4

CONTENTS Page

LEARNINC OBJECTIVES ...................................................................................................4

1 SOLDERING ................................................................................................................6

1.1 Soft Soldering ...................................................................................................... 6

1.2

Maintenance of Soldering Irons ...........................................................................6

1.2.1

Preparation.......................................................................................................6

1.2.2 Shapes of Soldering Irons Most Frequently Used............................................7

1.3 Types and Purposes of Flux ................................................................................8

1.4

Soldering Procedure ............................................................................................9

1.4.1

Conditions to be Fulfilled When Soldering .......................................................9

1.4.2 Correct and Defective Joints..........................................................................10

1.4.3

Soldering of a Wire Into a Terminal Tag ........................................................11

1.5 Defects...............................................................................................................13

1.6

Manual Soldering of Printed Circuits..................................................................15

1.6.1 Faults .............................................................................................................15

1.7

Flame Soldering (Used for Soft Soldering) ........................................................ 16

1.7.1 Procedure for Flame Soldering ......................................................................17

1.7.2 Precautions When Flame Soldering...............................................................18

2 CLASSIFICATION OF ELECTRICAL TEST INSTRUMENTS....................................19

2.1

Continuity ...........................................................................................................19

2.1.1 Ohmmeter ...................................................................................................... 19

2.2

Voltage Testing ..................................................................................................21

2.2.1 Voltage Testers..............................................................................................21

2.2.2 Test Lamps ....................................................................................................22

2.3 Insulation Testing...............................................................................................24

2.3.1

Insulation Testers...........................................................................................24

2.3.2

Measuring Resistance Between Conductors ................................................. 25

2.3.3 Measuring Resistance Between Conductors and Earth.................................26


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3 MEASURING TECHNIQUES - GENERAL.................................................................28

3.1

Measured Qantities............................................................................................28

3.2 Instruments for Measuring Voltage ....................................................................28

3.3 Instruments for Measuring Current ....................................................................29

3.4 Instruments for Measuring Resistance ..............................................................30

3.5 Measuring Circuits .............................................................................................30

3.5.1 Measurement of Voltage................................................................................30

3.5.2

Measurement of Current ................................................................................ 30

3.5.3

Measurement of Resistance .......................................................................... 31

3.5.4 Measurement of Current and Voltage............................................................32

3.6 Identifying Symbols on Measuring Instruments .................................................32

3.6.1

Position Symbols............................................................................................32

3.6.2

Symbols for Different Types of Current..........................................................33

3.6.3 Measuring Instruments...................................................................................33

3.7

Procedure for Taking Precision Measurements.................................................33

4

SAFETY REGULATIONS FOR ELECTRICAL INSTALLATIONS..............................35

4.1 Safety Regulations for Construction and Operation...........................................35

4.2

Safety Regulations for Shutting Down an Electrical Installation.........................35

4.3 Safety Regulations for Electrical Hand Tools.....................................................37

4.4 Safety Regulations for Ladders..........................................................................39

4.5

Safety Regulations for Working with Poisonous Substances.............................42

4.6 Rules to Ensure Safety at Work.........................................................................43

5 ACCIDENT PREVENTION.........................................................................................45

5.1

General ..............................................................................................................45

5.2 Effects of Electric Current on the Human Body..................................................46

5.3 First Aid in the Event of Electrical Accidents......................................................46

5.3.1 First Aid.......................................................................................................... 47

5.4

First Aid for General Accidents .......................................................................... 47


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BASIC ELECTRICITY 4

LEARNINC OBJECTIVES

The trainee should

state the meaning of the term "soldering''.

state the working temperature of soft soldering and hard soldering.

name the four parts of an electrically heated soldering iron.

sketch the most frequently used types of soldering iron.

state the types and uses of solder and flux.

list the steps in the correct procedure for making a soldered joint.

name the causes of a defective soldered joint and state the associated symptoms.

state the precautions which should be taken when using flame soldering.

state the reason for using flame soldering and detail the procedures.

sketch various continuity testers and their operation.

state the main features of the construction and method of Operation of a standard test

lamp.

state why faults in test instruments can cause electrical accidents. state reasonable

values of the insulation resistance for various mains voltages.

state three factors which must be taken into account when taking measurements with

a magneto-type insulation tester.

list exactly the procedures for taking a measurement with an insulation meter.

distinguish between the terms "measure" and "test".

distinguish between measured quantity and measured value.

name the correct measuring instruments for the quantities to be measured.

read measurements accurately.

sketch the basic circuits for measurement of current, voltage and resistance.

assign the appropriate terms to the abbreviations for measuring instruments.

observe all rules for ensuring the operational safety of an electrical installation.

comply with safety rules when working on electrical installations. check for faults on

hand tools.

name two of the most frequent causes of accidents at work. state the regulations for

the use of ladders.


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list the protective measures to be taken when working with liquid gases or acids.

state the level of currents and voltages which are dangerous for human life.

recognise the consequences and effects of injuries due to electric current.

take measures to eliminate the cause of accidents.

give assistance with "First Aid", if qualified.


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BASIC ELECTRICITY 4

1 SOLDERING

Soldering is the joining of metals by means of a molten filler metal (solder) which has a

melting point below that of the bare materials. Depending on the minimum working

temperature, to which the parts being soldered must be heated in order to begin the

soldering process, soldering is divided into:

- soft soldering - with a working temperature below 450C

- hard soldering - with a working temperature above 450C.

1.1 Soft Soldering

The form of soldering most frequently used in the electrical and electronic industries is soft

soldering. Soldering irons, with a power between 10 and 100 Watts, are used to heat the

point to be soldered.

1.2 Maintenance of Soldering Irons

Electrolytic copper tip (bit).

File as rarely as possible. If filling is necessary use longitudinal strokes followed by fine

polishing (transverse scratches impede the flow of solder). Shape by hammering; the tips

of soldering irons should only be cooled in air. If the tip is filed, it should be tinned.

1.2.1 Preparation

The surface must be metallically clean. Heat up the soldering iron until the solder spreads

over its surface. Tin the point with the aid of the soldering flux; wipe off excess solder with

a cloth.


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a) Copper tip (bit)

b) Heating element

c) Handle

d) Lead and plug

1.2.2 Shapes of Soldering Irons Most Frequently Used

Soldering iron with hammer-head tip

Pointed tip soldering iron

The soft solders for heavy metals are usually tin-lead alloys. Cored solder is generally

used for soldering electrical equipment.

There is a standard code for solder:

LSn 50 Pb = 50 % Sn + 50 % Pb; melting point = 210C.

LSn 60 Pb = 60 % Sn + 40 % Pb; melting point = 190C.

Sn = tin; Pb = lead.


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Cored solder consists of a tube of solder surrounding a resin core (distilled pine resin),

which acts as the flux.

1.3 Types and Purposes of Flux

There are two types of flux:

- Active flux

Active flux has a chemical action and removes the oxide film and grease from the

metal surface. The residual active flux must be removed from work after soldering.

NOTE:

Never use active flux on electrical work!

The typical active fluxed suitable for other than electrical work includes: Zinc chloride

solution (killed spirit); Ammonium chloride solution.

- Non-active flux

Heat and moisture will not convert the residual non-active flux into a harmful agent.

Typical non-active fluxes are resin (powder or paste) and tallow, which is commonly

used by plumbers for wiped joints.


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Purposes:

- They reduce the surface tension of the motten solder to approximately 1/3 as a result

of which it flows better.

- They dissolve light oxide layers on the metal.

- They protect the soldered joint against oxidation.

In order to be sure that after soldering the work metal does not suffer damage from the

flux, cored solder is used (because it has resin flux). It may be necessary to employ

another type of flux for tinning (mixture of tallow and sal-ammoniac, soldering fluid), i.e.,

for iron, resistance material and large soldered areas. These operations must always be

carried out away from the equipment so that the vapours given off when the flux vaporizes

do not damage parts of the equipment.

After use, remains of the flux must be carefully removed (wash off with trichlorethylene).

1.4 Soldering Procedure

1.4.1 Conditions to be Fulfilled When Soldering

- Mechanical sound joint.

- Electrically conducting joint.

The mechanical connection must first be made because both hands are used for

soldering. The pint of the soldering iron is held with one hand against the workpiece to

heat it. Some solder must always be supplied to the point of the tip to provide a large

contact area, thus ensuring optimum heat transfer.

When the workpiece has reached the soldering temperature the other hand is used to

transfer solder to the workpiece from the other side (not to the tip of the soldering iron).

The soldering iron and the solder are then removed and the soldered joint is allowed to

cool without vibration.


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NOTE:

Any remains of solder must be cleaned occasionally from the tip, (preferably with a damp

cloth) or if it has become covered with scale due to overheating, it must then be retained.

1.4.2 Correct and Defective Joints

Depending on the type of joint and it's position, the soldering iron is used from below or

from the side. The contours of the Part being soldered should just be visible.

Only very thin wires should be twisted together, otherwise it is difficult to separate the

soldered joint in the event of errors. Protruding ends of solder and wire should be cut off

after soldering. If possible not more than two wires should be connected to one soldered

joint.

Correct joint: the solder has a brightly polished surface and a smooth solder fillet.

Cold joint (dry joint): the surface is generally bright

but the fillets are not formed.

Cause: the solder was fed into the joint before the

metal parts to be joined had been adequately

heated.


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Burnt joint: the fillet solder is formed, but the surface of the

solder is matt (rough).

Cause: the temperature of the soldered joint was too high.

The flux had vaporized before it could remove the oxide

from the soldered joint.

Cracked surface; cause: the soldered joint was subject to

vibration when cooling.

Solder on one side:

Cause: the solder was not fed to the surface of the

workpiece but

incorrectly to the tip of the solder.

1.4.3 Soldering of a Wire Into a Terminal Tag

- Make a mechanically firm connection. Do not hold the wire in the hand!

If held in the hand:

- the flux vaporizes;

- heat cannot be properly conducted to the

soldering point;

- the supply of solder cannot be controlled;

- the soldered joint is impaired by movement and

a dry joint (cold joint) will exist even though the

application of heat is for an excessive period of

time.


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- Apply pressure to the connecting wire so that it is gripped in the soldering tag. This

saves time when soldering. If necessary, attach provisional bridging wires on one side,

then re-solder correctly on both sides.

- Clean the soldering iron. Dab fresh solder on the point of the

- Soldering iron and flick it off (make sure that the tip of the soldering iron is not loose);

the clean iron is now bright, but dry.

- When possible support the hand holding the soldering iron.

- Ensure that there is a good transfer of heat.

Position the soldering iron correctly. With small

parts, dry contact with the soldering iron is

sufficient and the two parts are held together.

With large components a small amount of solder

is applied to produce a better transfer of heat; the

soldering iron heats the part via this bridge of fluid

solder. (Apply the most heat to the large part).

- Soldering Process:

Make thermal contact.

Apply the solder, with the solder and the

soldering iron on opposite sides.

Melt off excess solder under pressure.


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Withdraw the solder and the soldering iron and Shake the remaining solder of the

soldering iron.

1.5 Defects

Heated for too long. Work more quickly. The

solder becomes stiff, forming points (flux is

vaporized).

Incorrect application of heat (or poor wire

material). Only wire heated. A cold joint exists

though started correctly.


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Incorrect application of heat (or soldering

iron too small). The transfer of heat to the

large part is too far forward. The soldered

joint is cold in places; the solder does not

flow, forming bulges.

A joint of insufficient size is formed for the

reason shown, or due to applying the solder

incorrectly. This may occur when the solder

flows away from the joint (when this

happens, always apply fresh solder).

Excessively large joints are thus formed.

Soldering joints at an angle: first apply heat

and solder on the right, then solder on the

left and withdraw the soldering iron.


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1.6 Manual Soldering of Printed Circuits

Press the soldering iron onto the connecting wire

and copper foil, feeding in fresh solder at the side;

then, still maintaining pressure on the wire and foil,

quickly withdraw the soldering iron and the solder.

1.6.1 Faults

The component and the connecting wire moved

(stressed).

The connecting wire is too short. the joint is weak

due to a poor transfer of heat when soldering; the

result is a cold joint.

Too much solder is used.

The bead of the solder is heated for too long,

impairing the adhesion of the foil (also caused by

soldering for too long).


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No thermal contact with the foil

(is the surface clean?).

No thermal contact with the connection.

(dry joint on wire).

The hole is too large.

The hole has a burr.

(clean surface with a few strokes of an

oilstone).

1.7 Flame Soldering (Used for Soft Soldering)

Flame soldering is soldering with a blowlamp or blowtorch.

A blowlamp is used when the heat of a soldering iron is insufficient, that is, for large parts

and if the joint cannot be reached satisfactorily with a soldering iron.


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Gas blowlamp (blowtorch)

The preparation for flame soldering is the same as that for using a soldering iron (clean

the surfaces thoroughly, press parts together and apply flux).

1.7.1 Procedure for Flame Soldering

- Heat up the parts, slowly and evenly, with the flame, to the soldering temperature.

- Use poor conductors of heat as a support for the part when soldering (asbestos,

fireclay etc.).

- Direct the flame on the part (not on the solder).

- The solder must be caused to melt by the heat of the parts (not by

- the flame).

- If the thickness of the parts is not the same, direct the flames on the thicker part.

- When the solder has flowed satisfactorily, remove the flame immediately (do not

overheat).

- Do not move the parts before the solder has solidified.

- After cooling clean any remnants of flux from the joint.

For soldering large surfaces "soldering paste" can also be used; this consists of a mixture

of powdered solder and flux.


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The soldering paste is spread on the work. The part is then heated to the soldering

temperature with the blowlamp.

The supply of heat takes place through the work piece with the larger mass (correct

method).

The work piece with the smaller mass is heated more than the larger. The solder melts in

the flame (wrong method).

1.7.2 Precautions When Flame Soldering

The use of an open flame always involves the risk of accidents and fire.

Therefore, the following precautions should be taken:

- Prior to use, check that the equipment is serviceable.

- Do not leave any inflammable objects or liquids near the flame (if possible cover with a

protective asbestos sheet).

- Have means available for extinguishing fires (fire extinguisher, water and sand).

- Protect your hands, hair and clothing from the open flame.

- Close the valve of the blowlamp or burner immediately after soldering has been

completed.


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2 CLASSIFICATION OF ELECTRICAL TEST INSTRUMENTS

- Instruments for continuity testing.

- Instruments for voltage testing.

- Instruments for insulation testing.

2.1 Continuity

2.1.1 Ohmmeter

For testing whether current is flowing through a conductor, simple resistance meters

(ohmmeters) or special continuity testers can be used. An ohmmeter consists of an

ammeter with a scale calibrated in ohms (), a balancing resistance for zeroing and a

voltage source (dry battery).


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Continuity testers usually consist of a voltage source and an optical or acoustic indicator

(light or buzzer).

Circuit of a continuity tester with indicator lamp. Range from 0 to approximately 100.

Function: if the circuit is closed and if the resistance Rx is sufficiently low or it is a

conductor, then the light comes on.

The circuit of a continuity tester with buzzer. Range from 0 to approximately 200.

Function: if the circuit is closed and the resistance Rx being measured is sufficiently low or

a conductor, then a buzzer sounds.

Some continuity testers have both a signal lamp and a buzzer. The test range can be

extended up to 5000 by incorporating a transistor for circuit amplification.


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X1, X2, X3 = terminal sockets

V1 = transistor for current amplification

H1 = filament lamp

H2 = buzzer

S1 = lamp switch

G1 = flat battery

Continuity testers with optical and acoustic indication (transistor buzzer) can also be used

as pocket lamps.

2.2 Voltage Testing

Voltage testers and test lamps are used to determine whether a voltage is present in

appliances or equipment. These Instruments do not enable the value of the voltage to be

measured.

2.2.1 Voltage Testers

These usually take the form of a screwdriver with an indicator lamp (neon lamp) in the

handle.


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How is it indicated whether the voltage is direct or alternating? With direct voltage only

one electrode (the negative pole) lights up; with alternating voltage, both electrodes light

up.

The circuit is connected to earth via the human body; a series resistance must, therefore,

be incorporated to reduce the current through the neon lamp to a harmless level.

The disadvantage of voltage testers is that they light up at very low currents (i.e. normal

insulation leakage currents) and, therefore, may give a false indication of voltage.

Voltage testers have a working range between 100 and 750 V.

2.2.2 Test Lamps

These Instruments incorporate incandescent lamps and are used to determine the voltage

level. In contrast to voltage testers, the lamps are connected across the voltage source. If

the test lamp signals the existence of a voltage, this indicates that there are no breaks or

high resistances in the circuit. The working range of a low voltage test lamp ranges from

about 100 to 500 V.


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With many types, some illumination of the lamps is visible at 42 V. Since there are no

commercial 500 V incandescent lamps two identical shockproof lamps, each with a rated

voltage of 250 V, are connected in series.

Test probe, handles knurled and shielded to prevent the hands from slipping.

Procedure: when testing the absence of voltage between conductors, test conductor

against conductor but always test each conductor with respect to earth.

Many electrical accidents occur only because defective test instruments were used, and

these fall to register the voltage.

NOTE:

For voltage testing all test Instruments must be checked for safety and satisfactory

operation prior to use.


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2.3 Insulation Testing

After completion of an electrical Installation the condition of the insulation must be

checked.

NOTE:

The resistance of the insulation (Rins) should be measured between conductor and

conductor, and between conductor and earth. It should not be less than 1000 0 per Volt of

the working voltage in dry and damp rooms (gives a leakage current of 1 mA; British

regulations require insulation resistance of not less than 1 M).

Calculate the appropriate resistance of the insulation in a distribution sub-station for a

leakage current of 1 mA:

220 V a Rinsof 220 k380 V a Rinsof 380 k

500 V a Rinsof 500 k

2.3.1 Insulation Testers

These are resistance-meters (ohmmeters) with very high measuring voltages (between

500 and 1000 V) and measuring ranges up to 1000 M.The measuring voltage (direct voltage) is generated by a hand driven d.c. generator or a

battery inverter.


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Hand-operated insulation tester

NOTE:

The positive pole is, therefore, connected to earth so that the leakage current does not

have electrolytic action (salts increase the contact resistance). Testing is performed with

direct voltage. This should not be less than 500 V.

A battery inverter changes direct voltage into alternating voltage, and by the use of a

transformer this AC voltage is stepped up to a value between 500 and 1500 V. A rectifier

then converts it back into direct voltage.

2.3.2 Measuring Resistance Between Conductors

- Disconnect the equipment from the voltage source.

- Switch on all switches, so that the switch circuit will also be measured. Disconnect the

consumer loads (remove lamps, disconnect motors etc.).

- Take measurement.


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Lighting mains (220 V)

Between phase conductor and neutral conductor.

Three-phase mains (380 V)

Between two of the phase conductors.

2.3.3 Measuring Resistance Between Conductors and Earth

- Disconnect the equipment from the voltage source (switch off).

- Switch on all the switches and consuming loads.

- Test the entire equipment - between conductor and earth.


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In sound installations Rins. is usually higher than 10 M; values of about 0.5 M may

indicate faulty insulation.


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3 MEASURING TECHNIQUES - GENERAL

Measuring techniques can be divided into true measurement, and testing. True

measurement is the determination of a completely unknown quantity, i.e., a voltage or

current.

The sole purpose of testing is to establish whether a prescribed value, termed the "desired

value" exists and the limits within which it lies i.e., the cell voltage of an accumulator or the

water temperature of a radiator.

The measured quantity is the physical quantity to be measured (i.e., voltage, current,

electrical resistance etc).

The measured value is the value obtained from the reading of a measuring instrument; it

is composed of the numerical value and the unit of the measured quantity (i.e., 3 V, 4 A, 5

).The reading is given by the position of the pointer on a scale.

3.1 Measured Quantities

A distinction is made between:

- Instruments for measuring voltage (U).

- Instruments for measuring current (I).

- Instruments for measuring resistance (R).

3.2 Instruments for Measuring Voltage

The magnitude of a voltage is measured with a voltmeter. The two terminals of the

voltmeter are connected to the poles of the voltage source.


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NOTE:

Voltmeters have a high internal resistance and a low current consumption. The coil can

have a large number of turns of thin wire.

3.3 Instruments for Measuring Current

The magnitude of a current is measured with an ammeter. The two terminals of the

ammeter are connected directly into a closed circuit (in series).

NOTE:

Ammeter coils have a low resistance and a low voltage drop. The coil can have a few

turns of thick wire. When connected directly to the voltage source the Instrument can be

damaged by high currents.


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3.4 Instruments for Measuring Resistance

The resistance of a resistor is measured with an ohmmeter. Before measuring the

resistance of a component, external voltage sources must be disconnected.

See paragraph 2.1.1 "Ohmmeter" (page 19).

3.5 Measuring Circuits

3.5.1 Measurement of Voltage

NOTE:

When testing direct voltage, check that the positive terminal of the measuring instrument

is connected to the positive side of the voltage source. The measuring range of the

voltmeter must be suited to the value of the voltage being measured.

3.5.2 Measurement of Current


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NOTE:

To obtain a reading on an ammeter a current must flow through the measuring instrument.

The load being measured is in series with the ammeter. The measuring range of the

ammeter must suit the value of the current being measured.

3.5.3 Measurement of Resistance

NOTE:

The measurement of resistance is a measurement of current; a voltage source is

connected in series with the measuring instrument. If a resistance is connected to the

ohmmeter, a closed circuit is formed, and charge-carriers flow through the measuring

instrument; these indicate the measured quantity on the scale which is calibrated in ohms.


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3.5.4 Measurement of Current and Voltage

Ammeters are connected in the circuit in which the current is to be measured; voltmeters

are connected across points between which the voltage difference is to be measured. An

ammeter must, therefore, only produce a low voltage drop, that is, its terminal resistance

must be low.A voltmeter, by contrast, must only take a low current, that is, its terminal resistance must

be as high as possible. When it is required to measure current, voltage and resistance

with one measuring instrument universal meters are employed. The instrument can be

adapted to suit the particular types of current and measured quantities by means of

selector switches or plugs. Before taking any measurement it is important to see the

selector switch to the largest measuring range and then to adjust it, in steps, to the

measured value. The measuring instruments are generally moving-coil instruments, with

an integral measuring rectifier for measurement of alternating quantities.

3.6 Identifying Symbols on Measuring Instruments

3.6.1 Position Symbols

Vertical position

Horizontal position


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Inclined position with angle of inclination; i.e.:

3.6.2 Symbols for Different Types of Current

Direct current

Alternating current ~

Direct and alternating current

3.6.3 Measuring Instruments

3.7 Procedure for Taking Precision Measurements

- Measuring instrument stationary in the specific working position.

- Sufficient distance from iron masses (about 10 cm) and from heavy-current power

lines.

- The pointer must coincide with the "zero" line when the measuring instrument is de-

energised. lf not, this must be corrected by adjusting the zero knob.

- Avoid polishing the glass disc during measurement because the static charge may

affect the reading. Such charges can be removed by breathing on the glass.

- When using instruments with a range-selection facility (Multi-meters) it is advisable,

before commencing to protect the Instrument by selecting a large measuring range,

and to adjust the quantity to be measured, in steps.

- Reading errors due to parallax.


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When distance between pointer and scale is small:

When the distance between pointer and scale is large:


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4 SAFETY REGULATIONS FOR ELECTRICAL INSTALLATIONS

Every year many people suffer injuries as a result of using electrical appliances;

sometimes this involves serious burn and, in an alarming number of cases, death ensues.

It is the duty of the electrician to protect both himself and his colleagues against this

danger.

For the safety of our colleagues the highest importance must be accorded to the

prevention of accident at work. In any work concerned with the generation, transmission

and use of electric power, specific standards and rules apply (service and operating

instructions).

4.1 Safety Regulations for Construction and Operation

An electrical installation must always be constructed and operated so as to comply with

the following rules:

- there must be no danger to life or to the human body

- the electrical installation must not cause damage to material or property (fire)

- if possible operational safety should be high to achieve fault-free operation.

4.2 Safety Regulations for Shutting Down an Electrical Installation

(Working on machines and transformers etc.)

- Switch off all poles of the supply.

- Take precautions to prevent any switches from being re-closed.

- Earth the circuit and short-circuit, the conductors.

- Check that all parts are voltage-free.

- Cover adjacent live parts and isolate the dangerous points.

Switch on; do this in the reverse sequence.

The technical specialist must protect the layman!!


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Various aids are necessary to comply correctly with these rules.

Example:

WARNING NOTICES


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Special caution is required when working on high-voltage equipment (1000 V and above).

Only trained personnel may, therefore, be employed on this equipment.

4.3 Safety Regulations for Electrical Hand Tools

Special attention must be paid to the various electrical hand tools (hand drills, grinding

wheels etc.), especially flexible leads to lights and plugs. Take defective equipment out of

service immediately and repair it (renew defective leads immediately). Observe the rules

for relieving tension in drives and for preventing rotation. Check that the earth conductor is

not broken at any point. Also check that electrical appliances, switches, Installation

equipment etc., are marked with safety symbols.

Electrical installation (connections to dwellings, rising conductors etc.) must always becarried out in accordance with the regulations of the respective electricity suppliers.

When the design of the equipment does not comply with the regulations, the manufacturer

can be held liable for any damage which may occur. The electrician faces injury not only

from electrical current, lack of care, thoughtlessness and haste but also due to handling

defective tools.


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Some of the most common causes of accidents at work are:

- The use of faulty tools which can cause injury to the hands.

- The use of conductors which do not comply with regulations.

NOTE:

- The tools are the electrician's visiting card.

- The screwdriver should fit the slot in the screw.

- Check that the test lamp is working before use.

- Always wear goggles when operating a grinder.

- Chisels should not have any burrs.

- Keep hair short or wear a hairnet when operating machines.

- Check the handles of hammers.


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4.4 Safety Regulations for Ladders

Take special care when choosing ladders.

Ladders should have curb chains and rounded ends to the sides (pointed ends are

dangerous).

Cracked rungs and sides should always be repaired by an expert.


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The following rules should be observed when working on ladders:

- Set up ladders correctly and do not overload (chain must have proper tension).

- Do not use ladders which are too short; the top two rungs should be used as a hand

grip.

- When working near doors, lock them.

- Ladders should always be additionally held by a second man.

- Never place tools on the rungs of a ladder.

- Scaffolding is generally used on construction sites and requires special precautions

against accidents.

- Always use a safety belt (risk of falling).

- Keep tools in a tool bag.

- There should be railing around the scaffolding (risk of tools falling off).

- Always wear a safety helmet.


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4.5 Safety Regulations for Working with Poisonous Substances

The electrician also has to work with various poisonous substances and materials, such

as lead, high-lead content alloys, chemical compounds containing lead (red lead oxide) or

with acids and alkalis. Measures should, therefore, be employed to prevent any damage

to health.

To avoid lead poisoning:

- No smoking.

- No eating.

- Only work with a breathing

mask or extraction equipment.

- Wash hands frequently.


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When working with acids and alkalis:

- Wear goggles to protect the eyes.

- Wear special clothing to protect the body and hands against burns due to acid or

caustic substances.

- Pour slowly to prevent spillage.

NOTE:

Never pour water into concentrated acids, but the reverse.

Special precautions are also necessary when working with bottled gases (propane and

butane etc).

Protect bottles from exposure to sunlight or other heating effects.

Do not store in pits or cellars because leakage of gas can cause death from asphyxiation

(bottled gases are heavier than air).

4.6 Rules to Ensure Safety at Work

- Caution is the best protection against accidents.

- Work with tools and use the adequate protective means, according to regulations.

- Comply with accident notices and warning signs and read service and operating

instructions.

- When carrying out any work, observe the relevant regulations.


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5 ACCIDENT PREVENTION

Every employee must endeavour to cooperate in accident prevention. Should an accident

occur, appropriate "First Aid" can assist the healing process. Everyone should, therefore,

take a course in First Aid (Red Cross, Civil Defence etc.).

5.1 General

Currents exceeding 50 mA are highly dangerous to human beings. Such currents can be

attained with voltages of 65 V (when the contact area is large).

The strength of the current flowing through a man, who finds himself in the circuit,depends on the voltage and on the contact resistance. The contact resistance depends in

turn on the contact area, the contact pressure, the humidity and the voltage.

NOTE:

Higher contact pressure - lower resistance.

Severe moisture or damp - lower resistance.

The higher the voltage, the higher the current.

Conclusions

When there is a high contact pressure, large contact area, damp surface and voltages

greater than 100 V, the total resistance can be 1000 . For a mains voltage of 220 V,

according to Ohm's Law a current of approximately 0.22 A flows through the body (if the

person is sitting or standing in a bath the current could be as high as 1 A. Severe pains

are felt, and depending on the path taken by the current, there is uncontrolled contraction

of the muscles, similar to a cramp. The muscles then no longer respond to the signals

from the brain. The current produces pulsations in the heart, shock, and paralysis of the

respiratory system. Lack of oxygen causes destruction of parts of the brain which are

essential for life and the person dies.


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NOTE:

A four minute interruption of the oxygen supply to the brain can cause death or severe

damage if resuscitation of the person, who has stopped breathing, is not commenced at

once.

5.2 Effects of Electric Current on the Human Body

1 mA - perception threshold.

15 mA - cramp (the muscles no longer respond to the brain).

50 mA - danger level (prolonged action - highly dangerous).

100 mA - longer than 1 second - death.

High voltages are especially dangerous (more than 1000 V with respect to earth). Theyproduce very serious burns and usually cause death. Direct current is also dangerous,

although cases of death due to the passage of current through the body rarely occur.

Heavy arcing may however cause burns. Moreover, the chemical action of direct current

leads to decomposition of the blood and the internal organs.

First Aid must, therefore, be carried out rapidly and resolutely, but without haste. Above

all, one should not endanger oneself or others.

5.3 First Aid in the Event of Electrical Accidents

The circuit must be switched off immediately (i.e., switch off the main switch, withdraw the

plug etc.), taking care to insulate oneself. Wrap the hands in a dry cloth or piece of

clothing and insulate the feet from the ground with insulating materials such as rubber. In

the case of high voltages switch off first because it is dangerous to approach the injured

person.


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5.3.1 First Aid

Immediately move the unconscious person on to his side (do not administer anything) so

that his mouth - the lowest point - faces downwards, allowing mucus and blood (in the

case of fall) to flow out. If breathing has ceased, begin artificial respiration immediately.

One hand under the chin, the other on the forehead of the unconscious person frees the

respiratory passages (incline the head well back). Remove any objects from the mouth

(i.e., false teeth).

Take a deep breath and blow your breath into the nose of the unconscious person

(mouth-to-nose resuscitation). If this is delayed, blow into the slightly open mouth (mouth-

to-mouth resuscitation). Repeat this respiration until the arrival of the rescue service or the

doctor. If circulation ceases (heart failure) begin massaging (heart) at once. This provides

a last chance, otherwise death to the injured person can result.After stimulating breathing with the mouth, press the lower breastbone against the spine

with rapid strokes five times in succession; this will compress the heart, and the blood,

enriched with oxygen, is conducted to the brain cells; they cannot become paralysed.

NOTE:

One mouth resuscitation to five breast compressions. Inform the doctor and rescue

service. Place a guide to lead the doctor to the accident place. Inform the police of the

accident (obligatory!).

5.4 First Aid for General Accidents

Lay the injured person down in a comfortable position, protecting him against cold, heat

and damp etc.

In the event of fractures, dislocations, position limbs comfortably. As the use of

anaesthetics may be necessary later, do not give the patient any food or drink.


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Do not wash lacerations or contused wounds with the exception of acid burns; cover with

sterilized bandages and dress the wound; leave further treatment to the doctor.

Stop any heavy bleeding by finger pressure or by a pressure bandage (tourniquet). In the

event of gas poisoning, provide access to fresh air (prohibit open flames due to risk of

explosion).

If the skin has suffered burns, wash with a copious supply of water. Clothing soaked in a

caustic substance should be removed immediately. When the eyes have been burnt by

caustic substances, wash them with water (10 - 15 minutes); protect the other eye

(syringes may have a harmful action). Apply or dry, sterilized dressing or bandage to the

burns. The use of oil, ointment and powder is forbidden.

Extinguish burning clothing with water or smother the flames with a blanket. If the injured

person feels a prickly or numb sensation in the spine, there is the risk of paralysis

(fractured vertebra). Take great care when laying the Patient down. The injured person

must remain in the body position as found until a doctor arrives to take over the

responsibility.


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EE 009

Basic Training Electricity 4

Theoretical Test


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BASIC TRAINING ELECTRICITY 4

TEST 1

1. State the meaning of the term "soldering".

2. Name the type of soldering most commonly used in electrical engineering.

3. Electric hand-tools can be damaged. Name the forms of damage which can cause an

accident.

4. Give the procedures for "First Aid" in the event of electrical accidents.

5. For voltage measurement the current through the measuring instrument must be kept

low; how is this achieved?

6. A measuring instrument is intended for use at an inclination of 60, and is designed for

AC measurement. Draw the symbols which indicate these characteristics an the

measuring instrument.

7. Special rules must be followed when testing for zero-voltage state these.

8. Describe the correct procedure for soldering a wire into a terminal lug.

9. When testing insulation, the positive pole is connected to the earth. Give the reason

for this.

10. Give the precautions which must be taken when working with an open flame.


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TEST 2

1. State the value of the electric current which is dangerous to human life.

2. An electrical Installation is to be put back into operation after stoppage for

maintenance work. Describe, in the correct sequence, the safety devices which must

be removed in order to connect a voltage to the Installation.

3. Draw a diagram of a simple continuity tester and explain its operation.

4. Name two instruments used for voltage testing.

5. State how to determine whether, when voltage testing, the voltage is direct or

alternating.

6. State two conditions which must be fulfilled by a soldered joint.

7. Explain the causes of a cold soldered joint.

8. State the rules which must be followed when working with acids.

9. State the procedure to be followed, when testing insulation resistance.

10. Sketch the symbol for a moving iron Instrument: for what kind of current is it used?


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TEST 3

1. Name the main parts of an ohmmeter and draw a circuit diagram of it.

2. During current measurement the voltage drop across the meter is very low. State the

reason why this voltage drop is low?

3. State the rules which must be complied with to make an electrical installation safe to

operated.

4. Name two factors which increase the current through the human body.

5. Name four parts of a soldering iron.

6. Sketch the circuit for measuring a voltage.

7. Sketch the circuit for measuring current.

8. State the regulations for the use of ladders.

9. State the purpose of fluxes.

10. What is the disadvantage of some voltage testers?


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TEST 4

1. Sketch the circuit of a continuity tester with an optical indicator and state how it

operates.

2. State the meaning of the designation for solder "LSn 60 Pb".

3. State the resistance of the insulation in the case of a fault current of 1 mA and the

following mains voltage = 200 V; 380 V; 500 V.

4. State the factors which are important for the measurement of direct voltage.

5. Name a second method of soft soldering, other than that of using a soldering iron, and

state what equipment can be used for this purpose.

6. Working with lead or lead compounds involves the risk of lead poisoning. Describe

ways of preventing lead poisoning.

7. State the current sufficient to produce the effects listed below an the human body:

Perception threshold above A

Cramp above A

Danger level above A

Death above A

8. Sketch the circuit for current and voltage measurement with an AC supply.

9. State the causes of a burnt soldered joint.

10. When testing insulation, at what speed should the handle of the magneto be turned?


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TEST 1

(Solution)

1. Soldering is the joining of metals with a molten filler metal (solder) which has a melting

point below of the metals being joined.

2. Soft soldering.

3. Faulty leads and plugs; no device for relieving tension and preventing twisting; broken

earth wire.

4. Break the circuit immediately, taking due to insulate yourself; i.e., wrap a dry cloth or

garment around your hands; insulate your feet from the ground with insulating

material, such as rubber etc. With high voltage equipment first switch off, because it is

very dangerous to approach injured persons.

5. The internal resistance of the meter must be very high. A large number of windings -

thin wire.

6. Symbol for position =

Symbol for alternating current = ~

7. Immediately before using checks that the test lamp or voltmeter is functioning correctly

and safety.

Check firstly between the conductors, and then always test between the conductor

and earth.

8. Clean soldering iron.

Make mechanical joint and apply flux.

Make thermal contact; position the bit of the soldering iron correctly.

Feed in solder; solder and soldering iron bit from opposite sides. Melt solder under

pressure.

Withdraw solder and soldering iron bit and flick residual solder off the bit.


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9. The fault current should not produce any electrolytic action.

10. Check that all operational equipment is safe.

Do not leave inflammable objects or fluids near an open flame. Have a fire

extinguisher ready.

Protect your hands, hair and clothing from the open flame.

Close the valve of the soldering lamp or burner immediately after completing

soldering.


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TEST 2

(Solution)

1. Currents over 50 mA cause death.

2. Remove protective covers.

Remove earth and short-circuit cables.

Remove closing devices (locks, warning panels).

Switch on installation.

Check voltage.

3. The current produced by the battery flows through the resistance to be tested. If there

is no break in the circuit the light (or buzzer) comes on.

4. Screwdriver with signal lamp and test lamp.

5. With direct current only one electrode of the neon lamp lights up - negative pole; with

alternating current both electrodes light up.


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6. Mechanically sound.

Electrically conducting joint.

7. The solder was fed in before the metal parts being joined had been correctly heated

up.

8. Wear special clothing to protect hands and eyes. Never pour water into concentrated

acids, but the reverse.

9. Disconnect the equipment from the voltage source (switch off).

Switch on all switches so that the switch line is also measured.

Disconnect consumer loads (unscrew filament lamps etc.).

Measure between outer conductor and outer conductor or outer conductor with

respect to the neutral conductor.

Switch on the consuming loads.

Measure between all conductors connected together, and earth.

10. Moving iron meters are used for direct current and alternating current.

Symbol:


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TEST 3

(Solution)

1. Ammeter with the scale calibrated in ohms; an adjusting resistance for zeroing; a

voltage source.

2. The low internal resistance of the measuring instrument, caused by a few windings

made of thick wire.

3. There should be no danger to life or physical safety. The electrical equipment shall not

cause damage to material (burning).

Functional reliability should be sufficiently high to ensure fault-free Operation.

4. High voltage level, low contact resistance.

5. Electrolytic copper tip (bit).

Heating element.

Handle.

Lead and plug.


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6.

The voltmeter is connected across to the voltage to be measured.

7.

The consuming load is in series with the ammeter.

8. Set up ladders correctly and do not overload.

Do not use ladders which are too short; the top two rungs should be used as a hand

grip.

When working near doors, lock them.

Ladders should always be additionally held by a second person. Never place tools an

the rungs of a ladder.

9. They reduce the surface tension of the fluid solder to about 1/3; it, therefore, flows

better.

They remove light oxide layers from metals.

The soldered joint is protected against oxidation.

10. The disadvantage of voltage testers is that they light up even at small currents

(insulation currents) and, therefore, often give a false indication of a voltage.


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TEST 4

(Solution)

1.

If the circuit is closed through the resistance Rx being tested, or through a conductor,

the signal lamp will light up.

2. LSn 60 Pb = 60 % tin (Sn) and 40 % Iead (Pb).

3. 220 V = Rins, 220 k; 380 V = Rins 380 k;

500 V = Rins 500 k.

4. With direct current ensure that the positive terminal of the measuring instrument is

connected to the positive pole of the voltage source. The measuring range should be

equal to or greater than the values of the voltage difference being measured.

5. Flame soldering = blow lamp or soldering burner.

6. No smoking or eating. Work only with a respirator or extraction apparatus. Clean

hands frequently.


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7. Perception level over 1 mA.

Cramp level over 15 mA.

Danger level over 50 mA.

Death level over 100 mA for longer than 1 second.

8.

Ammeters are connected in the circuit in which the current is to be measured;

voltmeters are connected across the point at which the voltage difference is to be

measured.

9. The temperature of the soldered joint was too high, the flux had vaporized before it

could remove the oxide from the soldered joint.

10. The crank should be turned at 2 - 3 rev/s.


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KEY TO EVALUATION

PER CENT MARK

88 100 1

75 87 2

62 74 3

50 61 4

0 49 5

EE009-Basic Electricity 4-Th-Inst.pdf

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