Domestic Electrical Installation.pdf 5b2m7

Prepared and com piled by M ichael H am m erl

Training Module on Domestic Electrical Installation


Table of Contents 1. 2.

Safety at the workplace ................................................................................................................ 1 Introduction.................................................................................................................................. 2 2.1 Electrical effects...................................................................................................................2 2.2 Heating effect .......................................................................................................................2 2.3 Lighting effect......................................................................................................................3 2.4 Magnetic effect ....................................................................................................................4 3. Electricity..................................................................................................................................... 5 4. Circuits and circuit diagrams ....................................................................................................... 6 4.1 Electromagnetic Force (E.m.f.) and Potential Difference (p.d) ...........................................6 4.2 Conductors and cables .........................................................................................................7 4.3 Loads ....................................................................................................................................8 4.4 Control .................................................................................................................................8 4.5 Protection .............................................................................................................................9 4.6 Resistors .............................................................................................................................10 4.7 Basic .........................................................................................................................10 5. Ohm’s Law................................................................................................................................. 11 6. Kirchhoff’s Law......................................................................................................................... 12 7. Resistors in series and in parallel circuits .................................................................................. 15 8. Waveforms ................................................................................................................................. 18 8.1 Properties of waveforms ....................................................................................................19 8.2.1 Frequency..................................................................................................................19 8.2.2 Period ........................................................................................................................19 8.2.3 Amplitude...................................................................................................................19 8.2.4 Root-mean-square (r.m.s.) ........................................................................................20 9. Decimal Units ............................................................................................................................ 21 10. Measuring Technology .............................................................................................................. 22 10.1 Introduction........................................................................................................................22 10.2 Accuracy of the instrument ................................................................................................22 10.3 Accuracy of your measurement .........................................................................................22 11. Meters ........................................................................................................................................ 22 11.1 Analogue meters ................................................................................................................23 11.1.1 Moving-coil meters ...................................................................................................23 11.1.2 Moving-iron meters...................................................................................................24 11.2 Digital meters .....................................................................................................................25 11.3 Multimeters ........................................................................................................................25 11.4 Measuring current ..............................................................................................................28 11.5 Measuring voltage..............................................................................................................28 11.6 Measuring resistance..........................................................................................................29 11.7 Symbols used for measuring-equipment scales .................................................................30 12. Domestic installation ................................................................................................................. 31 14. Symbols used for domestic installation ..................................................................................... 32 14. Reading construction plans ........................................................................................................ 37 15. Reading architectural diagrams.................................................................................................. 41 16. Installation materials and components....................................................................................... 44 16.1 Solid cable and wires .........................................................................................................44 16.2 Current carrying capacity of wires.....................................................................................45 16.3 Colour codes for wires .......................................................................................................46 16.4 Terminating of wires ..........................................................................................................47 16.5 Connecting a cable to a plug ..............................................................................................51 16.6 Connecting cables to a branching box ...............................................................................52


16.7 Soldering of wires to a terminal.........................................................................................53 16.8 Forming eyelets to single strand wires...............................................................................54 16.9 Termination of coaxial cables ............................................................................................56 16.10 Installing cables and conduits ........................................................................................57 16.11 Portable electric drill utilisation.....................................................................................61 17. Domestic electrical installation.................................................................................................. 66 17.1 Types of circuit diagrams...................................................................................................67 17.1.1 Connection plan ........................................................................................................67 17.1.2 Schematic diagram ....................................................................................................67 17.1.3 Installation diagram...................................................................................................68 17.2 Mains connection ...............................................................................................................68 17.3 Protective conductor connection........................................................................................68 17.4 The plan for an installation ................................................................................................69 14.4.1 Perspective view .......................................................................................................69 17.4.2 The ground plan ........................................................................................................69 17.4.3 The installation plan..................................................................................................70 17.4.4 Fuses..........................................................................................................................70 18. Circuit diagrams......................................................................................................................... 71 18.1 One pole ON / Off circuit ..................................................................................................71 18.2 Two pole ON / Off circuit..................................................................................................72 18.3 Group switching.................................................................................................................73 18.4 Serial circuit .......................................................................................................................74 18.5 Change-over circuit............................................................................................................75 18.6 Intermediate circuit ............................................................................................................76 18.7 Impulse switching ..............................................................................................................77 18.8 Stairway illumination.........................................................................................................80 18.9 House siganl installation ....................................................................................................82 18.10 Fluorescent lamp ............................................................................................................85 18.11 Stroboscopic effect.........................................................................................................87


1.

Safety at the workplace − The workplace occupies a lot of your daily time, so that should be the reason to arrange it in a way, that the work can be done relaxed and efficient. − The whole workplace with its tools, materials and equipment also has to be arranged in such a way that accidents are impossible to happen − Damaged tools must not be used − Tools must only be used for the purpose they are made for − Do not give access to your workshop to persons who are not aware of electrical hazards − Keep your workplace always clean and in order − To avoid electrical hazards, the floor under your workplace has to be insulated − Chemicals, which can affect the health of human beings, or can cause any damage to tools, material and equipment and installations, have to be stored in a locked compartment. − Good light is always essential to perform good fine mechanical work

It is strictly forbidden to work with any electrical part while it is live! Therefore are some laid down regulations to guarantee this. These regulations are known as the five rules of safety 1. Switch off the voltage 2. Ensure that the voltage is not switched on while working 3. Ensure that there is no voltage *****Confirm by measurement**** 4. Earth and short circuit 5. Cover all neighbouring parts Begin to work

Courage does not consist of knowingly and heedlessly exposing oneself to danger by ignoring the rules of safety. Courage consists of sticking to ones principles in the face of derision form ones colleagues.

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2.

Introduction

We usually recognise electricity by the way it changes material and objects in the world around us. Electricity is, after all, invisible and silent. Before you can begin study electronics you need to know about electricity. And in studying electricity, we must begin by considering what it does to other things. 2.1

Electrical effects

You can see, hear or even measure electricity directly, but it can be detected by the way it affects matter. Electricity interacts in five important ways: Produce heat Produce light Affect chemical reactions Cause and be caused by magnetism Have a mechanical effect 2.2

Heating effect

One of the most important physical effects caused by electric current is heat. The heating effect of an electric current is used in many items of electrical equipment – cookers, electric heaters and lamps for example – and it is something that must be considered when deg and electrical apparatus. Without considering how it works at this stage, let us consider a source of electrical energy. It might be a battery, or a special laboratory power supply. If this is connected to an electric lamp, as shown in Figure 1, electrical current will flow through the lamp.

Figure 1: A simple circuit with circuit diagram

After a minute or so, carefully feel the envelope of the lamp. It will be warm, perhaps even hot. If is not to bright, look closely at the filament inside the lamp. What makes it light up? The answer is that the filament is glowing white-hot. The envelope of the lamp is filled with an inert gas, usually argon, to prevent the filament from burning up in an instant. The lamp lights only when both wires are connected to the power supply. Electric current must be able to flow from the power supply, through the lamp, and back to the power supply. As the electric current flows round in a circle, we call this an electrical circuit.

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Figure 2 shows a battery converting electricity into heat. Heat is dissipated by a component called a resistor; see below for an explanation of this component. A power supply capable of providing at least 0.5 amps should be used. The resistor will get too hot to the touch after a short time.

Figure 2:A simple circuit like this will dissipate heat

2.3

Lighting effect

Electric current can be used to produce light. In the section above, we saw how a lamp filament can be heated to such high temperature that it glows white-hot and gives off light. But this is not direct conversion of electrical energy into light. Only recently has “light without heat” become reality. It can be demonstrated very easily using a light emitting diode or LED. Figure 3 shows a circuit with suitable values for the components. When the power supply is connected the LED will light up (observe polarity of the LED prior to connection). The light produced by the LED is a result of electrical energy being converted directly into light. Nothing has to heat up to produce the light.

Figure 3: A light emitting diode (LED) in a simple circuit

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2.4

Magnetic effect

Perhaps the most widely exploited effect is the magnetic effect of an electric current. This is used in all sorts of devices, electric motors to loud speakers. Whenever en electric current flows along a conductor, such as a wire, it is accompanied by a magnetic field. The simple apparatus shown in Figure 4 can demonstrate this. When the leads are connected to the battery a current flows through the circuit. The bulb is included in the circuit for two reasons: first, to indicate that the current is flowing; second, to limit the current to a safe level.

Figure 4: Magnetism: The magnetic effect of an electric current

Figure 5 shows a closer view of the com.

Figure 5: A close-up view of the wire and com alignment

Make sure that there are no large metal objects close to the com. With the current off, the com needle should align itself along the north-south axis of the globe. Carefully placed the wire so that it lies exactly along the line of the needle, electrical wires are made of non-magnetic metals, so the needle’s position will not be affected. Now connect the wires to the battery. The lamp will light, and the needle will be deflected. Without disturbing the com or the wire placed across it, reverses the battery connections (change polarity). How does the behaviour of the needle differ from the way it behaved in the first demonstration? It is clear from this simple demonstration that where there is a flow of current, there is also magnetism.

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3.

Electricity

What is electricity? This seems to be a good question with which to begin. To answer this question, we have to look at the composition of matter. All matter is, as we know made up of atoms, but it is far from simple to describe an individual atom. From a study of physics, any student will know that atoms are made up of nucleus, around which orbit electrons. But nobody really knows what an atom looks like, as the largest atom is far too small to see even with the most powerful microscope. So physicists design models of atoms to help them to explain atomic behaviour. Niels Bohr, a Danish physicist, proposed one of the simplest and most straightforward models of the atom in 1913. It is Bohr’s model that we most often think of, with its tiny electrons in orbit around the heavy nucleus. A Bohr atom model is illustrated in Figure 6

Figure 6: A model of an atom, according to Bohr's theory

The electrons are confined to orbits at fixed distances from the nucleus, each orbit corresponding to a specific amount of energy possessed by the electrons in it. If an electron gains or loses the right amount of energy, it can jump to the next orbit away from the nucleus, or towards it. Electrons in the outmost orbits are held to the nucleus rather more weakly than those nearer the middle, and can under certain circumstances be detached from the atom. Once detached, such electrons are called free electrons. It is important to realise that gain or loss of electrons does not in any way change the substance of the atom. The nucleus is unchanged, with the same number and kind of particles in it, and so an atom of say, copper can loss or gain electrons and still remain copper. Each electron carries one unit of negative electric charge. In a “normal” atom, the charges on the electrons are exactly balanced by the charge on the nucleus. An atom of copper normally has 29 electrons in orbit around the nucleus. Each electron has one unit of negative electric charge, and the nucleus has a total of 29 units of positive charge. If a copper atom loses an electron, the nucleus will be unchanged. But still it has a total of 29 units of positive charge, and there are only 28 electrons and thus 28 units of negative charge, the atom has overall, one unit of positive charge that is not balanced by a corresponding negative charge. Such an atom is called a positive ion or cation. Similarly, atoms can gain extra electrons. If a free electron meets a neutral atom, the electron may go into the outer orbit around the nucleus. In this case, there will be one more negative charge than needed for neutrality. Such an atom is called a negative ion or anion. What is an electrical charge? The real answer is that it is impossible to say in words just what electric charge is. It can be described mathematically, but this is not the same as describing it physically. At least we have a very clear and detailed idea of how electricity behaves, and this enables us to use it in all sorts of clever ways without actually needing an underlying understanding of the nature of electricity and electric charge. When looking at the physics of electricity, it is wise to that we are looking at models rather than real thing. Page 5 of 87


4.

Circuits and circuit diagrams

A good place to begin is to take a simple electrical circuit, and then look at its constituent parts. Figure 7 shows a simple battery and lamp circuit in two forms. In figure 7(a) it is shown as a picture, and in Figure 7(b) it is shown as a circuit diagram. Like most circuits, this circuit can be divided into basic parts: a source of energy, conductor of electricity, a load, a control device and a protection device.

Figure 7: A simple circuit shown (a) as a picture and (b) as a diagram

4.1

Electromagnetic Force (E.m.f.) and Potential Difference (p.d)

In this circuit the source of energy is a battery. Therefore the battery is the source of electric power. We could also use other sources of energy like a generator or a solar cell. The important feature is the fact that between the terminals of the battery there exists a potential difference (p.d.). Potential difference is measured in volts (V), named after the Italian physicist Alessandro Volta, who made the first practical battery. A p.d. is simply a difference in total electrical charge. Electrochemical reactions in the battery cause one terminal to contain many positive ions, and the other to contain many negative ions. The battery is a source of electromagnetic force (E.m.f.). Like p.d. it is measured in volts. There is a subtle distinction between the two. E.m.f. is the p.d. of a source of electrical energy, such as a battery. P.d., however, measures the difference in electrical potential between two points regardless of whether or not they are a source of energy; for example, it is possible to measure the p.d. across the terminals of an electric lamp, but nobody would suggest that the lamp is a source of electrical energy. The E.m.f. of the battery in Figure 2.10 is 12 volts.

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4.2

Conductors and cables

A conductor is a material that allows electric current to flow through very easily. All metals are good conductors, as are some other materials such as carbon. Almost all plastics are very poor conductors – insulators, in fact. An insulator is simply a material that is a bad conductor of electricity. One of the best insulators is glass. Most ceramics are insulators, along with rubber, oil or wax. A flow of electric current through a conductor consists of free electrons moving from atom to atom through the material. In order for there to be a useful amount of current, a very large number of electrons must flow. Accordingly, the basic unit of electric current flow is equivalent to around 6.28 x 1018 electrons per second moving past a given point in the conductor. This unit of electric current is called ampere (A), and is named after Andre Marie Ampere, a French physicist who did important work on electricity and electromagnetism.

Figure 8: A cross-section through two parts of cable

Figure 8 illustrates a cross-section through two different types of electrical wires. Look first a Figure 8(a). The wire consists of a central conductor that is surrounded by a flexible plastic insulation. The conductor is most likely to be made of tin-plated copper. Copper is one of the best conductors of electricity, only silver is better, and is also fairly flexible and relatively cheap. It is tin-plated to prevent the copper from oxidising; copper oxide is a poor conductor of electricity, which could give trouble if you used the cable with screw-type terminals. An oxidised surface is also difficult to solder. The insulation surrounding the conductor is usually made of polyvinyl chloride (PVC), a flexible plastic with excellent insulation properties and an extremely long life in normal use. Figure 8(b) shows a typical cable used in house wiring. This cable has three cores, or conductors. A second layer of insulation, the sheath, covers the three cores. The sheath not only provides insulation, but also gives mechanical protection to the insulated cores inside.

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4.3

Loads

The load in the circuit in Figure 7 is a lamp. In an electric circuit, a load is any device that uses electric power and dissipates energy. The lamp converts electrical energy into heat (and some light); this energy, which comes in the first place from the battery leaves the circuit entirely. A load in an electrical circuit can be one of a large range of devices: everything from an electric motor, lamp or bell to a house, which might be the load in a circuit of a large generator, or even a whole city. 4.4

Control

Almost every electrical device that uses power needs some form of control. Usually this takes the form of a switch or circuit breaker, to interrupt the flow of electric current in the circuit. Switches can be almost any size, according to the work they have to do. The circuit in Figure 7 requires only a small switch, as the amounts of current and voltage involved are quite small. Circuit breakers used at power generating stations have to interrupt very large currents and voltages and are sometimes the size of a small house.

Figure 9: (a) A low-voltage change over switch; (b) a modern slow-break micro gap mains switch

Figure 9 shows the mechanism of two typical switches. Figure 9(a) illustrates a low voltage change over switch, designed for use in low-voltage electrical equipment. Switches are rated according to their working voltage and current. This type of switch could interrupt currents up to 1A at voltages up to 100V; it is useful for battery operated appliances, but not for mains applications. Figure 9(b) shows a typical switch used in a house for controlling the lights in a room. It is intended for use at voltages up to 250V and currents up to 3A.

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4.5

Protection

A car battery is also a source of considerable energy. Although the voltage is low enough to avoid the risk of shock, the amount of current that the battery can deliver is substantial. If you were to connect the two terminals of a car battery together with a wire, the wire would immediately melt or burn. If you used a very heavy wire, the battery would explode. Either way, you would be in danger of serious injury. In the circuit of Figure 7 it should not be possible for this to happen. But accidents can always occur, so in any electrical system that has the potential for dangerous currents or voltages, protections devices are used. The simplest protection device is a fuse. A fuse simply consists of a thin wire, often sealed in a glass or ceramic tube. A typical cartridge fuse of this type is illustrated in Figure 10.

Figure 10: A typical cartridge fuse

The wire in the fuse is designed to carry a specific current before it begins to get hot and burn. For the fuse in Figure 7 the current rating is 1A. If current much higher than 1A is ed through the fuse, the thin wire inside gets so hot that it melts, breaking the circuit and interrupting the flow of electric current. So if something goes wrong with the lamp holder, causing the two terminals of the lamp to become connected together – “shorted together” is the usual technical expression - the fuse will prevent damage to the wiring or to the battery by interrupting the current. Without the fuse, the wiring might melt or the battery might overheat, causing fire. Fuses are available in a range of values, and the circuit designer uses one that has a current-carrying capacity that is just a little more than the highest current that is likely to flow in the circuit when it is working properly. The lamp itself can be a protection device of sorts. A lamp used in the circuit in Figure 1 to limit the current. Normally, the amount of current that can flow is not enough to light the lamp, but in the event of short-circuit (if the anode and cathode touch) the maximum current that can flow is limited by the lamp. The lamp also lights up, indicating that there is something wrong.

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A disadvantage of a fuse is that, once it has “blown”, it is useless and has to be replaced. If a circuit is often subject to fault conditions, this is inconvenient and expensive. In such circuits and over current circuit breaker could be used. This is a device that interrupts the flow of current by opening a switch when current increases above a certain level. Once the fault is corrected, the circuit breaker can be reset by simply pressing a button. An over current circuit breaker is illustrated in Figure 11.

Figure 11: Over current circuit breaker

4.6

Resistors

A resistor is a device, which is opposing electric current to flow, or in other words it is limiting the current flow in an electric circuit. Any load is acting as a resistor the circuit in Figure 7 has a lamp installed, this lamp is acting as a resistor and is limiting the actual current flow in the circuit. 4.7

Basic

Before starting with a scientific consideration of the electric circuit we have to agree on some basic terminologies, which are use by the technicians worldwide. Item

Current Electric charges Voltage Resistance Resistor

Description Current means the transport of electric charge inside a conducting material Electric charges are the free electrons in a conducting material The voltage is the potential difference (p.d.) between two points The resistance is that effect, which opposes the current A resistor is an electric component with a defined resistance

Symbol

Unit

I

A = Ampere

Q

C = Ampere x Second

U

V = Volt

R

Ω = Ohm

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5.

Ohm’s Law

Having described the main components of a typical electric circuit, we can now begin to look at the way in which the parts interact with each other. The E.m.f., current and electrical resistance of the load are related in a simple mathematical way, and in the next section we shall look at what is meant by “resistance”, and at the relationship of these three factors. The flow of electric current through a circuit depends on two factors: the E.m.f. and the resistance of the circuit. To get a visual picture of resistance it is convenient to think of the electric circuit as a plumbing system. Figure 12 shows such a comparison

Figure 10: Plumbing analogy of an electric circuit: voltage, current and resistance all have their equivalents in the water system

If the current flow is equivalent to a flow of water through a system, then the E.m.f. of the battery (in volts) is equivalent to the water pressure in the top tank (in kilograms per square meter). The flow of current (in amperes) in the circuit is equivalent to the flow of water in the pipe (in litres per minute). There is a restriction in the pipe that limits the flow. The amount of water that can flow out of the end of the pipe depends on the size of the restriction. If it is very thin, only a trickle of water will escape. In the electrical system, the equivalent of the restriction is a component called a resistor (because it resists the flow of electric current). The resistor has a greater resistance to the flow of current than the wires, just as the narrow part of the pipe “resists” the flow of water more than the rest of the pipe. Without the resistor, a much larger current would flow in the circuit, just as more water would flow out of an unrestricted pipe. But notice that the amount of water would still not be unlimited; the pipe itself puts a limitation on the flow. It is the same in the electrical circuit, for the wires and even the battery exhibit a certain amount of resistance that would, in the absence of anything else, limit the current to some extent. It is clear that, if the analogy holds good, there will be a relationship between pressure (E.m.f.), flow (current) and the size of the restriction (resistance). For example, if the water pressure where increased, you would expect a greater flow through the same restricted pipe. The German physicist George Simon Ohm first discovered the relationship between current, voltage and resistance in 1827. It is called Ohm’s Law.

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Ohm’s Law states that the current (I) flowing through an element in a circuit is directly proportional to the p.d. (V) across it. Ohm’s Law is usually written in the form.

U=IxR In words, this says that the voltage (in volts) equals the current (in amperes) times the resistance (in ohms). The unit of resistance, the ohm (Ω), is of course, named in honour of Ohm’s discovery. From the formula above we can see that a p.d. of 1 Volt causes a current of 1 Ampere to flow through a circuit element having the resistance of 1 Ohm. Given any two of the three factors, we can find the other one. The formula can be rearranged as follows:

I=

U R

R=

U I

Practical electrical and electronics engineers probably use this simple formula more than any other calculation. Given a voltage, it is possible to arrange for a specific current to flow through a circuit by including a suitable resistor in the circuit.

6.

Kirchhoff’s Law

In the 1850s, the German physicist Gustav Robert Kirchhoff formulated two more laws relating to electric circuits. These laws, named after him, enable us to write down equations to represent the circuits mathematically.

st

Kirchhoff’s Laws

1 Law:

The sum of the currents flowing into any junction in a circuit is always equal to the sum of currents flowing away from it.

2nd Law:

The sum of potential difference in any closed loop of a circuit equals the sum of the E.m.f. in the loop.

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Let us begin by considering the first of Kirchhoff’s laws. Figure 13 shows four wires; all carrying current and all are connected together. This is the sort of situation that occurs in almost any piece of electrical equipment. In Figure 13, there are two wires through which current flows into the junction and two through which current flows away from it. Adding together the currents flowing in, we shall get exactly the same values as we shall get for current flowing out. For Figure 13 this can be written as an equation.

I1 + I 2 = I 3 + I 4

Figure 11: The junction between four current carrying wires

Figure 14 shows a three-wire connection, in which one wire carries current into the junction and two carry current away. The equation for this junction is. I1 = I2 + I3

Figure 12: The junction between three current carrying wires

What Kirchhoff is saying is rather simple and obvious: current has to come form somewhere, and it has to go somewhere, it cannot just disappear.

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Now for the second of Kirchhoff’s laws. Figure 15 shows a simple circuit consisting of a source of E.m.f. and two resistors. The source of E.m.f. is a 12V battery and the resistors have values of 47Ω and 56Ω. We can use Ohm’s law to determine the total current flowing in the circuit.

Figure 13: A simple circuit containing two resistors

I=

U R

I=

12V 47Ω + 56Ω

I=

12V 103Ω

I = 0.1165A

We can use Ohm’s Law again to calculate the p.d. across each resistor.

U1 = I ⋅ R

U1 = 0.1165A ⋅ 47Ω

U1 = 5.476V

U2 = I ⋅ R

U2 = 0.1165A ⋅ 56Ω

U2 = 6.524V

The sum of the p.d across the resistors is

Utot = U1 + U2

Utot = 5.476V + 6.524V

Utot = 12V

which is just what Kirchhoff’s second law predicts.

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7.

Resistors in series and in parallel circuits

It is possible to connect more than one load to a source of E.m.f., as we have seen above. Figure 16 shows two ways in which two loads, in the shape of resistors, can be connected to a battery. These resistors have a resistance of 10Ω and 5Ω.

Figure 14: Resistors (a) in series and (b) in parallel

In Figure 16(a) where current is flowing through one load it also flows through the other, the loads are said to be connected in series. In Figure 16(b) current flows through each load independently. The loads are said to be connected in parallel. How can we calculate the combined value of resistance, as “seen” by the battery? For resistive loads connected in series, the values are simply added together. The combined resistance, Rtot of the loads connected in series is given by the simple formula Rtot = R1 + R2 + R3 + ………. (the dots mean that you can add as many numbers as you like) In Figure 16(a), this is Rtot = 10Ω + 5Ω, therefore Rtot = 15Ω which is about as simple as you can get.

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The second case, illustrated in Figure 16(b), is less easy to calculate. The formula for working out a combined parallel resistance is

1 1 1 1 = + + + ...... Rtot R1 R2 R3 In case only two resistors connected in parallel have to be calculated the following formula can be applied.

Rtot =

R1 ⋅ R2 R1 + R2

This means that the reciprocals of the values of the resistances, added together, give the reciprocal of the answer. Working this out for Figure 16(b) we get.

1 1 1 = + Rtot 10Ω 5Ω

⇒

1 = 0.1Ω + 0.2Ω ⇒ Rtot

1 = 0.3Ω ⇒ Rtot = 3.33Ω Rtot

Utilizing the other formula should provide us with the same result

Rtot =

10Ω ⋅ 5Ω 10Ω + 5Ω

⇒ Rtot =

50Ω 15Ω

⇒ Rtot = 3.33Ω

The combined resistance of the 10Ω resistor and 5Ω resistor, connected in parallel, is 3.3Ω.

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Calculate the total resistance (Rtot) as it is “seen” by the source of E.m.f. for the circuits given below.

Rtot =

Rtot =

Rtot =

Rtot =

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8.

Waveforms

So far the description of current has involved a flow of charge in one direction only. This is called Direct Current (DC) and is the current, which is caused to flow when a battery is connected across any device. A DC waveform, as shown in Figure 17 must have the same constant direction, even though its value from one second to the next might vary.

Figure 15: A DC waveform

An Alternating Current (AC) is one that is continually changing its direction. The simplest AC waveform is that of a sine wave, and as can be seen in Figure 18 both the magnitude of the current and its direction changes repeatedly, going from zero to a maximum positive value, falling back to zero again before going to a maximum negative value, and then returning to zero to complete the cycle. Like DC, the flow of AC is due to the presence of an E.m.f. or p.d. However, in this case it must be an alternating E.m.f. or p.d. For all ohmic conductors, i.e. conductors obeying Ohm’s Law, an alternating E.m.f. causes the flow of an alternating current with a waveform similar to the of the e.m.f. as shown in Figure 18.

Figure 16: An AC current and voltage waveform

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8.1

Properties of waveforms

Properties of a waveform associated with all alternating waveforms ore the frequency, period and amplitude or peak value.

Figure 17: Properties of a waveform

8.2.1

Frequency

This is the number of cycles of the waveform occurring each second. Frequency is measured in hertz (Hz), one hertz being defined as one cycle per second. A thousand cycles per second is called a kilohertz (kHz) and a million cycles per second, a megahertz (MHz). One thousand megahertz is called gigahertz (GHz). 8.2.2

Period

This is the time for one cycle of the waveform, measured in units of a second (s), millisecond (ms), or microsecond (µs). The period is simply the inverse of the frequency.

Periode =

8.2.3

1 Frequency

Frequency =

1 Period

Amplitude

This is the peak value of the waveform. It measures from zero to the maximum positive to the maximum negative value of the alternating voltage or current. The amplitude is therefore measured in the same unit as the magnitude of the waveform. The peak-to peak value measures from the positive maximum to the negative maximum and is therefore twice the amplitude.

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8.2.4

Root-mean-square (r.m.s.)

This is the average for an alternating voltage or current, defined as that steady D.C., which would produce the same heating effect. For the sine wave shown in Figure 19, the r.m.s. value is given by

r.m.s. current =

peak current 2

= peak current ⋅ 0.707

Similarly,

r.m.s. voltage =

peak voltage 2

= peak voltage ⋅ 0.707

The mains supply is an alternating voltage of r.m.s. average of 240V, a peak value of 339V and a frequency of 50 Hz. Thus the peak value of the mains is approximately 100V greater than the average and as a result constitutes a serious safety hazard.

Figure 20 shows again the values of a sine wave with the r.m.s. indicated.

Figure 18: Values of a waveform

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9.

Decimal Units

For some applications in electrical engineering and for most applications in electronic engineering, the ampere and volt are rather large units. The ohm, by contrast, is rather a small unit of resistance. It is normal for these three units to be used in conjunction with the usual SI (System International d’Unite’s) prefixes to make multiplications and submultiples of the basic units. A chart of the units is given below. Prefix Tera Giga Mega Kilo Milli Micro Nono Pico Femto

Symbol T G M k m µ n P f

Meaning x 1012 x 109 x 106 x 103 x 10-3 x 10-6 x 10-9 x 10-12 x 10-15

When working out Ohm’s Law calculations, it is vital that you to work in the right units. You cannot mix volt, kiloohm and milli amperes!!!!

Calculate the following equations:

R=

I=

10V = 50mA

15V = 3 kΩ

U = 150MΩ ⋅ 500mA =

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10. Measuring Technology 10.1 Introduction Electricity cannot be measured directly, but only its effects. The effects are manifold, and therefore also the measuring techniques. All measuring techniques have in common, that they need some energy (except mechanical measurements). This energy has to be delivered from the circuit where the measurement takes place. Consequently, the energy, which is necessary to feed the measuring instrument, has to be as small as possible. The measuring process should not have any influence on the function of the circuit, which undergoes a measurement. High demand on accuracy and / or little available energy requires often special measuring procedures and expensive measuring equipment.

All measuring equipment, no matter if it is a ruler, a calliper, a multimeter or an oscilloscope, have to be handled carefully to retain its accuracy 10.2 Accuracy of the instrument No item of test equipment is 100 % accurate. A test meter may well have a basic accuracy of ± 10%. Meters that have a basic accuracy as good as ± 2% are likely to be very expensive. Fortunately, practical electrical and electronic circuit seldom call for very accurate measurements. 10.3 Accuracy of your measurement It is a basic law of physics that you cannot measure something without affecting it in some way. It is worth ing this. For example, if you put a meter designed to measure current into a circuit, then the presence of the meter itself will affect the current flowing. Whether it affects the measurement significantly depends on the design of the meter and on what you are trying to measure with it. 11. Meters Today, both analogue and digital meters are available, and both are in common use. The earliest measuring instruments were analogue in nature, and we shall begin looking at this type. An analogue meter uses a pointer, needle or other indicator to point to a scale that is calibrated in volts, amps etc. The dictionary definition of the word “analogue” is the movement of the pointer of an analogue meter moves in sympathy with the quantity being measured. The larger the quantity, the further along the scale the pointer moves.

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11.1 Analogue meters 11.1.1 Moving-coil meters Most analogue meters use movements (the movement is the mechanism that moves the pointer) that are based on magnetism. Figure 21 shows the most common design, the moving-coil movement. The principle is simple. The coil and meter pointer are mounted on bearings (often jewelled, like a watch) so that the coil can rotate. Two small hairsprings, like the balance of a clockwork watch, resist the rotation and normally hold the coil in a fixed position, with the pointer at one end of the scale. The coil is located in a strong and constant magnetic field, that of a permanent magnet.

Figure 19: A moving-coil meter

When a current is ed through the coil, a magnetic field is created by electromagnetism. The orientation of the filed is such that it rotates the coil against the springs. The amount that it moves depends upon the strength of the electromagnetic filed, which in turn depends upon the amount of current flowing through the coil. It is convenient to use the hairsprings themselves to carry the current to the coil. Moving-coil meters are made in many shapes and sizes, according to the application. Electrically, they are specified according to three main parameters: Coil resistance, sensitivity and accuracy. The coil resistance is just what it sounds like: the electrical resistance of the moving coil, in ohms. This can be any value form just a few ohms to several kilo ohms. The sensitivity of a meter is often quoted as the full-scale deflection, or FSD for short. It is measured in amps (or more often in milliamps or micro amps), and is the amount of current that has to flow through the meter coil to make the pointer move to the far end of its scale. Another useful measure of sensitivity which includes the resistance of the coil (FSD does not) is given by

S=

RM VFSD

Here RM is the resistance of the meter movement coil, and VFSD is the voltage required to produce full-scale deflection. The sensitivity, S, is given in ohms per volt. This parameter may also be quoted by the manufacturers. The accuracy of the meter is given as a percentage tolerance, in just the same way that a component such as a resistor has a tolerance value. A meter with a sensitivity of 1 mA and an accuracy of ± 20 % is a meter that will give a full-scale deflection of its pointer for a current ranging from about 800µA to 1,2 mA. This does not mean that the meter will vary by that amount from time to time, just that the meter may depart from its specification by ± 20 %. Page 23 of 87


The repeatability, a fourth parameter, of measurements will be much better than this, and is related to the mechanical construction of the meter: the quality of the bearings, for example. Moving-coil meters are not cheap and tend to be used only when there is no effective solid-state substitute, such as indicator lights. A low-cost moving-coil meter might have an accuracy of ± 20%; the best and most expensive models will have an accuracy of better than ± 1 %. 11.1.2 Moving-iron meters An alternative to the moving-coil meter movement, cheaper to make but less accurate, is the moving-iron meter movement. The basic construction of a moving-iron meter is shown in Figure 22. This shows more the common repulsion moving-iron meter, based on the fact that two pieces of soft iron a repelled and move away form each other if they are magnetised so that they have the same polarity (either north or south). There is another design; called an attraction moving-iron meter, but most manufacturers use repulsion movements.

Figure 20: Repulsion-type moving-iron meter

When a current flows through the coil, a magnetic filed is created by the solenoid and both soft iron rods become magnetised. Clearly, they will both be magnetised in the same direction, so they will repel each other and move the pointer along the scale, against the controlling spring. The more current flows through the coil, the more powerful will be the repulsion and the further along the scale the pointer will move. All moving-coil meter movements are effectively damped – that is, prevented from swinging too rapidly – by magnetic effects. This damping is not present in moving-iron meters to the same extent, so some kind of extra damping, usually a simple air brake, is needed. The air resistance of a small vane in the air-damping chamber (Figure 22) prevents the pointer from moving to rapidly along the scale, but does not introduce any long-term effects. An important difference between the moving-coil meter and the moving-iron meter is that the moving-coil meter involves a magnetic field produced by a permanent magnet and the moving-iron meter does not. This means that the moving-iron meter can be designed for use with AC or DC whereas moving-coil meters will work with DC only.

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11.2 Digital meters Modern electronic has come up with an alternative to the analogue meter, in the form of the digital meter. A digital meter is a complex piece of electronics, and it displays a value in the form of numbers instead of having a pointer moving along a calibrated scale. Digital meters have many advantages compared with analogue meters and a few disadvantages. Advantages: − Easy to read: the output is in form of a number and it is not necessary to look carefully at a scale to determine an exact value − More accurate: price for price, digital meters can be made more accurate than their analogue counterparts. − Stronger: the digital meter has no meter movement that can be damaged by hard knocks − Smaller: the most accurate digital meter still only needs a few numbers for the display, whereas an accurate analogue meter needs a large scale so that you can read fine divisions Disadvantages − Suitable only for constant values. When a current or voltage is steadily changing an analogue meter will track the changes. A digital display will be an unreadable blur of numbers − Require a power source: the electronics in a digital meter needs a power source, usually a battery to function − Sometimes misleading: the display may show a value to three decimal places of a value, but the meter may be far less accurate than it seems. 11.3 Multimeters The multimeter is one of the most useful items of test equipment that an electrical or electronics engineer can have. Basically, it is a sensitive meter movement, fitted with a whole array of shunts1 and series resistors that can be selected by means of one or more multipurpose switches. The range and function controls are made as convenient as possible for ease of use. A good multimeter might have the functions and ranges listed in the table bellow. Multimeters from different manufactures will have rather different ranges, but the table gives a good idea of what is average in a good-quality instrument

1

In general a synonym for parallel. A resistor, usually of a relatively low value, that is connected in parallel with a measuring instrument. Only a friction of the current in the main circuit es through the instrument so that the shunt increases the range of the instrument.

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DC Voltage 0 – 0.1V 0 – 1V 0 - 10V 0 – 100V 0 – 1000V DC Current 0 - 100µA 0 – 1mA 0 – 10mA 0 – 100mA 0 – 500mA 0 – 10A Resistance 0 - 100Ω 0 – 1kΩ 0 – 100kΩ 0 – 10MΩ

AC Voltage 0 – 0.1V 0 – 1V 0 - 10V 0 – 100V 0 – 1000V AC Current 0 - 100µA 0 – 1mA 0 – 10mA 0 – 100mA 0 – 500mA 0 – 10A

The input resistance is a factor that is independent of the ranges available, it is the measure of the sensitivity of the meter. A sensitivity of 20 KΩ per volt is typical for the best analogue instruments. Clearly, all else being equal, a meter that loads any p.d. under measurement the least (by putting across the highest possible resistance) is the best. A meter of high sensitivity will also present the lowest resistance when measuring current. The table includes a range for the measurement of resistance. This is a simple function of a multimeter, using Ohm’s Law. The multimeter is fitted with a low-voltage source of e.m.f., usually a small battery. To measure resistance, the source of e.m.f. is connected across the resistance to be measured, and the resulting current can be read on the meter scale directly in ohms. The better the meter are equipped with a means of stabilising the battery voltage, for accurate resistance reading.

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A selection of different Digital Multimeters

A selection of different Analogue Multimeters

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11.4 Measuring current

Current is measured using either an ammeter or a multimeter and is measured in amp, milli amps or micro amps. The way in which current is the same, regardless of which meter is used. The circuit is broken at the point where the current measurement is required and the meter is connected in series with the other components of the circuit as shown in Figure 23. Note that the positive terminal is connected to the positive side of the circuit and the negative terminal is connected to the negative side.

Figure 21: Measuring current

11.5 Measuring voltage In electronics most voltage measurement is in fact a measure of the difference in voltage between two regions of a circuit. This is called the potential difference or p.d., as discussed earlier, and is measured in volts. Potential is measured with the respect to zero, ground or the negative side of the circuit. To measure a voltage or a p.d. the voltmeter is connected across, in parallel with , the component, as shown in Figure 24. Note that the negative side of the meter is connected to the negative side of the component and the positive side of the meter to the positive of the component.

Figure 22: Measuring voltage

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11.6 Measuring resistance Resistance is the opposition presented by the component to the flow of current. It is measured in ohms and is usually measured using a multimeter. To measure resistance, the meter is first switched to the highest ohm range. It is zeroed by touching the two leads together and turning the zero adjusts of the meter until the pointer is on zero. N.B. This only applies for analogue meters and not for digital meters The component is connected between the leads and the position of the pointer noted. If the pointer is not approximately in the middle of the scale then the range should be changed to bring the pointer in to the middle. It is important to zero on the new range before reading the scale. The resistance is the scale reading multiplied by the range setting.

A meter set to measure resistance should never be connected across a component in which which a current is flowing.

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11.7 Symbols used for measuring-equipment scales Symbol

Description Moving-coil measuring mechanism Moving-coil ratio meter Moving-magnet measuring mechanism Moving-iron measuring mechanism

Symbol

Description Measuring mechanism with magnetic screen Measuring mechanism with electrostatic screen A static measuring mechanism D.C. instrument

Electrodynamic measuring mechanism

A.C. instrument

Iron-cored electrodynamic mechanism

D.C and A.C. instrument

Electrcodynamic ratio measuring mechanism Iron-cored electrodynamic ratio measuring mechanism Induction measuring mechanism Bimetallic measuring mechanism Electrostatic measuring mechanism Vibration measuring mechanism Thermocouple, general Moving-coil measuring mechanism with thermocouple Insulated thermocouple Rectifier Moving-coil measuring mechanism with rectifier

Three-phase A.C. instrument with 1 measuring mechanism Three-phase A.C. instrument with 2 measuring mechanism Three-phase A.C. instrument with 3 measuring mechanism Vertical mounting position Horizontal mounting position Inclined mounting position, with indication of angle of inclination Zero resetting devices Test-voltage symbol The number in the star indicates the test voltage in kV (Star without figures: 500V test voltage

Warning (consult operating instructions) Instrument does not comply with regulations with regard to test voltage

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12. Domestic installation Electrical energy is the most important modern form of energy, owing to its many advantages. − − − −

It is not environmentally harmful in use It can be transmitted economically It is readily convertible to other forms of energy Large amount of energy can easily be controlled and regulated

It is clear, that electrical energy is also very convenient for domestic use. That is the reason, that like in any other fields of technology, a standard of technical requirement has been developed. Responsible for the distribution of electricity is the local supply authority. This responsibility usually ends with the delivery of electricity to a terminal at the object to be supplied. This however does not mean, that everyone is permitted to carry out electrical house installations. The local supplier usually has the right to decide upon qualifications of an electrician. Consumer installations are connected to a low-voltage network via buried cables or overhead lines, depending on the local conditions. The so-called private connection commences at the point where the supply line branches off from the main cables. Low-voltage supply means the provision of a voltage of 220/380V. This voltage is widely used as a standardized alternating voltage with a frequency of 50Hz. It is, however a voltage high enough to be fatal for any living creature when handled or installed in the wrong way. Electric safety standards and regulations therefore always have the top priority at electric house installations. When planning a house installation, the transmission capacity (current carrying capacity) of the cable to an installation has to be calculated. The data of those cables are standardized and available form the supplier. The terminal of the mains cable from the supplier of the electricity is a box (or cabinet) inside the consumer’s premises. This box carries the power consumption meter (which is sealed by the supplier), the mains fuse (or circuit breaker) plus the branch fuses. The following important regulations apply to the installation of private connection boxes. − They must be installed only in locations with no fire hazards − Special enclosures must be used in damp rooms or outdoor locations. − An arc-proof base has to be used for installation on wood − The box has to be placed under a protective cover if inflammable material may fall on it. The planning of electrical installations in residential accommodations must provide a sufficient number of sockets and wall outlets for the connection of appliances. Conductor diameters must be selected in accordance with the anticipated loads and adequate numbers of circuits must be provided The planning has to meet the requirements and regulations for the selection and dimensioning of the installation materials Besides the technical requirements, finally also minimizing the cost of a sufficient installation has to be taken in consideration.

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14. Symbols used for domestic installation Like in other filed of technology, also for domestic installations special symbols are used for drawing of electric circuit diagrams. These symbols are usually standardized in a country, but they are recommended only. Different symbols therefore may be found when studying different literature. Despite the differences which may be found, the circuit diagram has to be clear and being able to be read without any mistakes.

Think about, a mistake in reading a circuit diagram for a domestic installation may lead to fatal results.

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The above shown symbols are only a selection of many symbols used. Several symbols can be combined in one symbol Other fields of technologies have their own symbols, and a symbol used for domestic installation e.g. may have in the fluid technique another design. 14. Reading construction plans An architect usually designs the shape and construction of a house. He prepares the construction plans, which provide the technical information required to build the house. Masons and carpenters build the walls, floors, ceilings, doors, windows and the roof of a house. The sanitary installations such as the water pipes, the sanitary fixtures and the sewage pipes are installed by a plumber and the electrical installation providing illumination and electrical power is installed by a building electrician. As the electrical installation of a house is designed to suit its shape and construction, a building electrician must be able to read and interpret those construction plans, which are used to prepare the electrical installation plan. To show the layout of the rooms, walls, doors and windows of a house, the architect prepares the LAYOUT PLAN. The illustration below shows the principle of the layout plan by cutting the house into two pieces and remove the upper half.

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For practical reasons the layout plan is drawn as seen from above, giving us two of the dimensions required for the construction work. The length and the width. The layout plan shows also the place of each room in the house 1. 2. 3. 4. 5. 6. 7. 8.

Bedroom Bathroom Kitchen Dining and living room Entrance Toilet Storeroom Corridor

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The detailed measurement of the building and its rooms, walls, doors and windows are provided by the MASUREMENT PLAN. Using the metric system, the measurement should be given in centimetres (cm)

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These illustrations show in a pictorial way the example of an electrical installation for a single room. The main components of this installation are: − One light fixture to provide lighting in the room − Two installation switches to switch the light on and off from two different positions − Three socket outlets to provide electrical energy to various electrical appliances − Connecting lines, ing the various parts of the installation with each other − A branching box for the interconnection of some of the cables − The arrow shows the electrical supply to the installation

For practical reasons, the plan of an electrical installation is drawn on the layout plan of the respective construction. It is called the ARCITECTURAL DIAGRAM. It shows the electrical installation as seen from above. To avoid any confusion when reading architectural diagrams the doors have been omitted from the layout plans

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15. Reading architectural diagrams If you could lift out the complete electrical installations of a dwelling with eight rooms it would look similar to the illustration below. The electrical installation of each of the rooms is similar to the one shown earlier. Electricity is supplied to each room by supply lines. One end of each supply line is connected to a distribution centre and the other end is connected to a branching box in the room. In most electrical installations several rooms are connected to one supply line. In this particular case three supply lines are used for eight rooms, each of them supplying electricity to two or three rooms.

The electrical supply to the distribution centre is provided by a SERVICE CABEL, WHICH is connected to the distribution centre via a HOUSE CONNECTION BOX and an ELECTRIC METER.

As the incoming electrical supply and each of the outgoing supply lines are separately fused in the distribution centre, they are called the INCOMING and OUGOING CIRUITS. The above distribution centre has one incoming and three outgoing circuits.

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In the following architectural diagram of the electrical installation gives the following information: − It shows the layout of the installation − It shows the various circuits of the installation − It shows the position of each component and gives the required measurements − It shows the path to which the electrical lines have to be installed between the various components − It shows the method in which the installation is installed. In this case the components and connecting lines are installed on the surface of the walls and the ceilings. It is therefore called an ON SURFACE INSTALLATION. − It shows the various components of the installation, e.g. switches, socket outlets, light fixtures and specific

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In the following architectural diagram the components and the connecting lines are installed in the surface or flush to the surface of the walls and ceilings. It is therefore called an IN-SUFACE or FLUSH MOUNTED installations.

Can you identify all the symbols used in the diagram and can you spot the symbol denoting the flush installation of the components and connection lines

In this illustration the door of the room is shown as well as the direction in which the door opens, thus it is important to install the switch at the right place to enable the dwellers of the house to switch on the light when they enter the room.

Door

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16.

Installation materials and components

16.1 Solid cable and wires This illustration shows a simple electrical installation. An electric lamp is connected to a switch via a branching box. These components are interconnected with INSULATED WIRES. 1. 2. 3. 4.

Lamp Switch Branching box Insulated wires

The wires used in the above electrical installation consist of a CORE, which conducts electricity, and of an INSULATION COVER, WHICH does not conduct electricity.

1. Core 2. Insulation

The core of an insulated wire for general electrical installation work is mostly made of cooper and in some cases of aluminium. Both of these materials are GOOD ELECTRICAL CONDUCTORS. The insulation is mostly made of plastic material such as PVC or rubber. These materials are GOOD INSULATORS.

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There are also insulated wires with a core consisting of a few strands of wire. This type of wire is called multi-strand wire. It is also used for stationary installations. However it is easier to work with as it has a certain degree of flexibility.

Multi-strand wires with a core consisting of many fine strands of wires are very flexible. They are used for such electrical installations where the connecting lines are moved a lot. Multi strand wire with many fine strands is also used for the installation of control circuits in machines and equipment. Can you think of household appliances that are connected with a fine multi stand wires?? 16.2 Current carrying capacity of wires When you know the cross-sectional area of a wire core you can easily determine the current carrying capacity of the wire from the table below. Group I: Group II: Group II:

One or more single-core cables / wires in a conduit Multi-core cables, e.g. plastic sheeted cables Single-core cables laid free in the air or in a distribution box

Cross-sectional area in square mm 0.75 1 1.5 2.5 4 6 10 16 25 35 50 70

Maximum current carrying capacity in Amperes Group I Group II Group III 10 16 10 16 20 16 20 25 20 25 35 25 35 50 35 50 63 50 63 80 63 80 100 80 100 125 100 125 160 125 160 200 160 224 250

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16.3 Colour codes for wires Various colour codes are widely used to identify insulated wires in electrical installations. The colour code presently used in most countries is as follows:

As there are also other colour codes used in other countries, you must consult your instructor and ask him to explain to you the colour code used in your country. Generally it can be assumed that the colour code is as follows: Three wire system: Phase / Live Neutral Ground

black blue green/yellow

Five wire system:

black\ brown brown blue green / yellow

Phase L1 / R Phase L2 / S Phase L3 / T Neutral Ground

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16.4 Terminating of wires In order to connect the ends of insulated wires to the terminal of electrical components and branching boxes, etc., or to lugs and sleeves, the wires have to be stripped off at their ends to the length required for the particular type and size of the terminal connection.

To strip of the wire insulation use a wire stripper pliers.

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Close the pliers, loosen the lock nut and by turning the adjustment screw, adjust the closing point of the jaws in such a way that the jaws cut into the insulation but that they do not touch the core. When properly adjusted, the wire moves freely in the opening of the jaws when the pliers are closed.

Jaw adjustment for thin cores

Jaw adjustment for thick cores.

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Single strand wire ends, which are damaged by the jaws of wire stripping pliers, which have been adjusted too tightly, can break off easily and will cause breakdowns in electrical installations.

The jaws of wire stripping pliers, which are too tightly adjusted, can also damage multi-strand wire ends. The strands will be cut off and thereby weaken the wire and decrease the current carrying capacity at the terminal point resulting in heating up and finally start to burn down.

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When you have properly adjusted the wire stripping pliers, insert the wire end into the opening between the jaws to a position where the cutting edges of the jaws are in line with the marking to which the insulation has to be stripped

Close the pliers so that the jaws cut into the insulation.

Turn the pliers a half turn in order to cut the insulation all around the wire.

Pull the wire and the pliers away from each other to remove the insulation Check the wire end for dimensional accuracy and make sure it has not been damaged

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16.5 Connecting a cable to a plug

Open the cover of the plug with a screw driver

Open the cable retention clamp and loosen the terminal screws.

Trim the end of the cable to the shape and the dimension required by the plug you are working on. Use the illustration as a guide. Connect the cable according to the colour code used in your country.

Tighten the terminal screws and the cable retention clamp and close the plug.

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16.6 Connecting cables to a branching box In electrical installations the ends of wires and cables are connected to each other in branching boxes in accordance with the circuit diagram for that particular electrical installation

Using PVC insulated cables and a normal onsurface branching box with a terminal arrangement as show, the completed connection of the wire ends would look like this For proper insulation the ends of the cables should extend with their sheath or outer insulation into the branching box to the distance “D”. The distance “D” depends on the type and size of the branching box and ranges from approximately 5 to 10mm.

To avoid sharp bend and prevent wire ends from being under stress, they must be formed into slight curves, thus leaving a certain amount of slack wire for each wire end.

The following illustration shows again how a good connection has to be done for terminating a wire to a terminal.

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16.7 Soldering of wires to a terminal Heat up your soldering iron and melt a thin layer of solder over the face of its tip. The solder should melt immediately to a shiny surface, giving off a little white smoke. If the flux of the solder should char, clean the tip again with a linen pad. Now press the flat surface of the soldering iron bit on to the t as shown. Heat up the wire and the terminal.

Feed solder into the t as shown. As the solder melts, feed n more solder until the t is completely covered. Make sure that neither feed is too much nor too little with solder.

Remove the tip of the soldering iron from the t. Do not move the work piece, e.g. terminals or wire, until the t has cooled off and the solder is solidified.

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16.8 Forming eyelets to single strand wires

The eyelets are formed by using a pair of roundnose pliers.

Grip the very end of the wire between the jaws of the pliers at a place where the diameter of the conical shaped jaws corresponds approximately to the inside diameter of the eyelet to be formed.

Turn the pliers in the direction of the arrow and form a loop of the eyelet to the required size as shown.

Check the inside diameter by using the terminal screw.

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Having formed the loop to the correct inside diameter and to the dimension, grip it between the tips of the jaws of the pliers and slightly bend it in the direction of the arrow until the Fasten the wire end with its eyelet to the centre of the loop is in line with the axis of the terminal as shown above. Make sure that a flat wire. washer is used, and in certain cases also a lock washer between the screw-head and the eyelet as Check all dimensions and make sure that the shown. wire has not been damaged by the jaws of the Eyelets are always fastened in a clockwise pliers. direction otherwise the eyelet will be opened by the turn of the screw.

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16.9 Termination of coaxial cables

Coax cable must not be t to another length of coax by twisting or soldering the conductor together and wrapping with insulation tape. Where it is impossible to use one complete length of coax cable then a TROUGH COUPLER (or a back to back socket) has to be used to make the .

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16.10 Installing cables and conduits Cables and conduits can be fixed to the surface of a wall or any other construction by the use of clips or saddles

Clips are usually fastened with nails. Normal nails are used of the clips are to be fastened onto a wooden surface, but hardened steel nails are required or masonry surfaces,

Saddles are fastened with wood screws and a wall plug is fastened to a masonry surface and with screw only if fastened to a wooden surface.

For better of the cable, position the clips of horizontal runs of cables in such a way that their nails are places underneath the cable as shown in the illustration.

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When using this type of clip, nail all the clips of the run onto the installation surface at their market position as shown here. to use hardened steel nails when fastening these clips onto a hard masonry surface.

Proceed to install the cable run in the same sequence as explained.

Fasten the cable to the surface by closing the clips as shown here.

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For electrical installations in moist locations, this kind of saddle is often used to fasten cables or conduits to the installation surface

Remove the upper part of the saddles and with a screwdriver fasten the lower parts of all saddles for this cable run onto the installation surface.

Fasten the cable to the saddles by pressing the upper parts of the saddles onto the lower parts.

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To install two cables parallel to each other, use double clips or saddles which are available in many different types and sizes. They are installed as shown by these illustrations.

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16.11 Portable electric drill utilisation In order to drill holes into a masonry surface such as stone or concrete you will have to use a portable electric drill together with a masonry drill bit. A portable electric drill consists of the following parts 1. An electric motor which provides the rotary power for the drill 2. A switch to switch the motor ON and OFF 3. A lock button which can keep the switch in the ON position 4. A handle to hold the drill 5. A gear box which reduces the speed provided by the motor 6. A chuck which holds and turns the rotary cutting tools 7. A speed selector of the drill is build for two speed operation 8. A speed adjustment of the drill is equipped with an electronic speed control 9. A flexible cable with a plug to connect the drill to the electrical supply.

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Some portable electric drills are equipped with a PERCUSSION ATTACHEMNT. This attachment is used when drilling holes into concrete or stone. In addition to the rotary moment of the chuck it provides a movement in the direction of the axis of the drill, which is similar to the pounding of a hammer.

The percussion attachment can be engaged and disengaged by rotating a selector wheel behind the chuck. With most drills this attachment can be engaged or disengaged when the drill is on or off.

The position of the selector wheel or switch for the percussion attachment can be located also at a different location on the portable electric drill depending on the manufacturer of the drill machine.

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In this illustration you can see a masonry drill bit. It has the shape of a normal twist drill but its cutting edges are made from a very hard metal called carbide. The shank of the drill is mounted into the chuck of the electric drill. 1. Shank 2. Carbide tipped cutting edge

Masonry drills are available in diameters ranging from 3 to 25mm in steps of 0.5mm. The maximum shank diameter of the drills is 10 to 12mm. The overall length of these drills depends on their diameter. They are usually 70 to 150mm long but there are extra long versions ranging from 150 up to 220mm for drilling through walls.

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Before drilling the hole in a masonry surface you have to choose the size of the drill bit according to the wall plug used for your installation as shown in the illustration

To drill the whole hold the drill as shown with both hands and position id in such a way that the tip of the drill touches the surface.

Keep the drill at a right angel to the surface in order to produce a hole, which is also at right angles to the surface.

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The depth of the hole should be 2 or 3mm more than the length of the wall plug

When you have drilled and cleaned the hole, insert the wall plug with your fingers. Sometimes you may have to tap them in using a light hammer

To mount the device which has to be installed on the surface use a wood screw and attach the device to the wall be screwing in the wood screw and tight it firmly.

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17. Domestic electrical installation Electrical energy is conveyed to the consumers by the supply authorities via a three-phase network in form of a four-wire system consisting of the phases L1/R; L2/S; L3/T and the neutral conductor N. Modern systems, which provide a high standard of safety, providing additionally a protective earth conductor PE. Varieties of systems

Two-wire system: The classical distribution system does not provide a protective earth connector. Three-wire system: It is like the two wire system, also a one-phase system, but provides additionally a protective earth conductor.

Three-phase network: It is a four-wire system and most commonly used.

Five-wire system: Modern installations provide a PE to be able to protect sensitive installations by a special protective measures.

Distribution networks are subdivided as required into three, four or five wire systems. The symbols used are in accordance with IEC recommendations (IEC = International Electric Commission). An earth wire, which also acts as a neutral conductor may be represented by the letters PEN

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17.1 Types of circuit diagrams A circuit diagram is a comprehensive representation of a circuit, showing all its detail. Through a clear representation of the individual current paths it illustrates the way an electric circuit works. The circuit diagram should represent the electrical appliances and equipment in an installation and their interaction with sufficient clarity to facilitate the reading of the circuit. 17.1.1 Connection plan The assembled representation circuit diagram is also known as the CONNECTION PLAN. This representation is an all-pole representation, which means that all conductors are drawn.

Junction box to connect the wires

Lamp protection by a circuit protected conductor PE

Hand driven switch with a notch

17.1.2 Schematic diagram The detached representation of a circuit diagram is also known as a schematic diagram. This representation provides a high degree of clarity. The PE connection is not shown.

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17.1.3 Installation diagram The installation diagram is a single representation for lightning and power installations, which is as a rule drawn in its proper position on the building plan. The PE conductor figure as an additional conductor in the indication of the number of the conductors.

17.2 Mains connection When an appliance is to be connected an electrical conducting connection must be produced between the network and the appliance via a switch. In practice, the switch will be connected to the phase L1 and the return conductor is connected un-switched to the neutral line. The reason for this is that the general case is the off-position of the switch. For safety reasons as few parts of the installation as possible should be live.

17.3 Protective conductor connection A protective conductor is never to be switched A protective conductor, if present, should be connected to those parts of the appliance, which are capable of conducting electricity and being able to be touched. The local electricity supply authority prescribes the safety rules and regulations. The use of the neutral conductor N as a protective conductor is somewhat dangerous but it is possible to use it. Nevertheless, if Phase and Neutral are exchanged in it position, Phase will be connected to those parts of an appliance that should be protected.

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17.4 The plan for an installation The installation plan is the plan for the layout of the electrical installation. It can be drawn in 3 different ways. After completing work the installation plan should remain at the place of the installation. 14.4.1

Perspective view

17.4.2

The ground plan

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17.4.3

The installation plan

Most useful when comparing the 3 ways of drawing an installation plan, seems to be the ground plan with the installations As to be seen from the perspective view, the wiring has to be done only horizontally and vertical, but never diagonal. 17.4.4 Fuses When current flows through a conductor, heating occurs. The extend of heating depends on the magnitude of the current flowing. When the current is impermissible strong and the heating consequently also excessive the conductors and equipment will be destroyed and there is a risk of fire. To prevent this danger, electrical installations have to be disconnected at excessive high current. For this reason particularly sensitive points (planned interruption points) are introduced into the wiring system to break the circuit when the current is too high. These devices are called fuses. Fuses or circuit breakers are produced in a wide range according to the required applications If fuses are patched-up or bridged, there is no longer any planned interruption point. Patching-up or bridging of fusses is prohibited. Equipment or cables run the danger of being destroyed. There will also be the risk of fire.

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18. Circuit diagrams 18.1 One pole ON / Off circuit

Installation plan

Schematic diagram

Connection plan

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18.2 Two pole ON / Off circuit

Installation plan

Schematic diagram

Connection plan

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18.3 Group switching Two devices or two groups of devices can be switched only separately (one way or the other)

Installation plan

Schematic diagram

Connection plan

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18.4 Serial circuit Two devices or two groups of devices can be switched on or off together or separately

Installation plan

Schematic diagram

Connection plan

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18.5 Change-over circuit It permits the ON / Off switching of a lamp from two different places at any time of the two switches

Installation plan

Schematic diagram

Connection plan

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18.6 Intermediate circuit The lamp can be switched ON / OFF from several switches and at any position of the switches

Installation plan

Schematic diagram

Connection plan

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18.7 Impulse switching Instead of using a switch, which is manually operated, also an impulse switch can be applied. This impulse switch is a relay with bi-stable positions. This relay remains in its switching position after the first excitation. A reversal in its switching position follows after a second excitation. Two basic circuits with an impulse switch

In this circuit with an impulse switch, the control and the switching voltage are obtained from the same system (source).

In this circuit with an impulse switch, the control voltage and the switching voltage are from different systems (source).

The advantage of an impulse switch is, that with a low voltage in the control circuit a high voltage in another circuit can be switched. The excitation of the impulse switch requires only a very short time. Usually this short excitation is obtained through a push-button. Symbols used with impulse switching circuits

Impulse switch (symbol used in installation plans)

Push-button (symbol used in installation plans) Impulse switch (symbol used in schematic diagram)

Push-button (symbol used in electric diagram)

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Symbol for a transformer with insulation between input and output winding used in installation plan

Symbol used for a transformer in electric circuit diagram Impulse switching using the control and switching voltage from the same source Installation plan

Schematic diagram

Connection plan

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Impulse switching using for control and for switching voltage different sources

Installation plan

Schematic diagram

Connecting plan

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18.8 Stairway illumination The stairway usually should have an automatic lightning installation with two switching points and three lightning points. The cellar steps are equipped with an impulse switch for three switching and two lightning points. The automatic lightning installation provides the feature as follows: After the first excitation of the TIMER RELAY the light in the stairway will be on for the pre-set time of the timer relay. After the time is elapsed the light will be off until the next excitation. View of the installation works

Installation diagram

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Schematic diagram

Connection plan

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18.9 House siganl installation With a house signal installation a visitor at the entrance door can ring the bell in the desired apartment by pushing a button on the door . From the same apartment the entrance door can be opened by pushing the button for the operation of the door-opening magnet. Installation diagram

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Schematic diagram

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Connection plan

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18.10 Fluorescent lamp The fluorescent lamp is a gas filled glass-tube. The gas is mercury and some noble gas. Two heating coils are placed at the ends of the glass-tube. The glass is coated inside with fluorescent material. The fluorescent lamp itself can be operated only together with a starter and a ballast (choke). Sometimes a compensation capacitor is connected in parallel to the lamp.

Function of the fluorescent lamp The starter is a glow-lamp (also gas-discharge-lamp). It has high resistance in the state of not glowing, but due to ionisation of the gas a low resistance when glowing. The glowing starts when the voltage is applied. The glow heats up a bi-metal, which soon makes a connection, and a current flows through the heating coils inside the glass-tube. The heating coils are heated up. The bi-metal cools off and the current ing the starter will interrupt. This interruption of the current produces a high induction voltage by the ballast (choke). This high voltage fires then the fluorescent lamp. Once the lamp has fired, only the remaining voltage is needed. The ballast is limiting the current as needed. The maintaining voltage on the fluorescent lamp is smaller than the firing voltage of the starter. Some false starts are necessary to start the fluorescent lamp.

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After switching on a very small current is flowing which creates a glow discharge in the gas filled starter. This glow discharge heats up the bi-metal strip of the starter.

The bi-metal is closing the starter. Now a current 1,5 times of the actual lamp current is flowing. This current induces a very high magnetic flied in the choke (ballast). At the same time the filaments start to glow.

The bi-metal is not longer heated and opens again. The very high magnetic filed in the choke is decreasing rapidly. This change of magnetic filed in the choke results in a very high voltage output of app. 800V. This voltage surge ignites the gas in the lamp. After ignition the choke reduces the lamp current. It acts as a dropping resistor.

If two fluorescent lamps are connected in series it is called a TANDEM-CRICUIT. For this circuit only one ballast (choke) is necessary. The ballast has to be made for the power of both fluorescent lamps.

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18.11 Stroboscopic effect In a workshop where rotating machines are used such as lathe or milling machines, it is important to avoid the stroboscopic effect of fluorescent lamps. If this measure is not undertaken the risk of an accident can increase due to the fact that the stroboscopic effect will give the impression to the human eyes that the rotating part is stationary, not rotating, which is in fact not true. This effect is used in the automotive filed where ignition point and dwell are being measured with a stroboscopic lamp. When the discharge takes place in the gaseous envelope, there is a movement of ions and electrons, which reverses when the polarity of the supply changes, i.e. twice every cycle of the supply voltage. On a 50 Hz supply, this means 100 times every second. When this reversal if movement coincides with the speed of a revolving machine, the machine appears to be stationary, which presents an obvious danger. The following methods are adopted to reduce this effect. Where a three-phase-system supply is available, adjacent lamps are connected to different phases of the supply. The use of a twin-tube fitting where one tube has a capacitor connected in series with it to produce a phase-shift of the current in that tube as shown in the illustration below.

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