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TOPIC: 17. ELECTRICITY
INTRODUCTION: This section only teaches students the basics of electricity such as the technical terms; the different ways electrical power can be produced; the function of a fuse; different electricity accessories (tools, switches); connecting of lights, switches and power points to the power line and simple house wiring.
OBJECTIVES:
17.1. Students should be able to define technical terms like DC, AC, Active, Neutral, Earthing, Volt, Ampere and Ohm.
17.2. Students must be able to state the function of a fusebox and how many Ampere a fuse needs to secure lights and how many Ampere to secure power points,
17.3. To know the tools and accessories used in electrical installation work.
17.4. Students should be able to connect light switches and power points correctly.
17.5. Students should know how to install a simple wiring system in a house.
17.6. To define what a alternative switch means and how to make it.
METHOD:
17.1. Prepare for this lesson a battery light which you put in front of the class to show students one form of power which can be used.
Explain all the terms related to electrical power and what they mean. Students write it in their trade theory book.
17.2. Prepare a fusebox and demonstrate how wires are connected correctly and which fuses are used for main switch, power points and lights.
Prepare photocopies of a fusebox and students glue them in their trade theory books.
17.3. Prepare tools and accessories used for electrical installations and display them in the classroom.
Prepare photocopies of these tools to glue in the students book.
17.4. Prepare light, switch and power point to demonstrate how they are connected correctly to the power line. Prepare photocopies from the book for the students to glue in their trade theory book.
17.5. For this lesson prepare some lights, switches, power points, a fusebox and several meters of wire and connectors.
After explaining basic house wiring demonstrate it with the help of the students.
Before switching on the main fuse check all connections for correctness!
17.6. This chapter will only be explained because it is almost the same procedure as for chapter 17.5. the only difference being the connections to the switch. This system is rarely used in normal cases.
NOTE: At the end of this section prepare at least two worksheets for students to complete as homework in their nightstudies. Correct and assess them later.
Electricity has become an essential energy source in our daily lives. You are confronted with it everywhere. We use it during our work, at home and even for entertainment. If it is produced in a hydroelectric power station, it is very environment friendly too. The function of a hydro-electric power station is quite simple. The water of a river is directed into a channel. This channel leads to a turbine. The turbines driving-wheel is turned by the current of water. Because the turbine is connected to the generator, it gives the generator the turning movement and the generator is able to produce electrical energy.
DC: - Direct current, electric current flowing in one direction. Eg. Battery. When the direct current flows, the lamp is able to light.
Figure
AC: - Alternate current that reverses its direction at regular intervals, the cycle being repeated continuously, the number of completed cycles per second being known as frequency. The symbol for frequency is hertz (Hz). It means one hertz stands for one cycle. We have 50 hertz per second which means 50 cycles for one second. Frequency = 50 Hz. The alternate current is produced by the generator. It does not matter if it is driven by a turbine or a diesel engine.
Active: - Where the electric current starts to move, never touch this wire. It will give you a shock. It is marked with plus (+).
Neutral: - Where the electric current flows. It is marked with minus (-).
Earthing: - Earthing prevents you from getting a shock. Always connect the green-yellow wire to the earth when you connect a light, switch, powerplug or powerpoint.
Volt: - Volt is the unit for voltage. Voltage is the amount of electrical power in an electrical circuit if it is not interrupted. The electrical power is always 250 Volt. The word comes from the Italian physician Allesandro Volta who realised the force of electric energy.
Ampere: - Ampere is the electrical force. It is named after a French physician Andrew Marie Ampere. You can compare it with a bucket of water, if one bucket of water is equal 250 V. If you switch on a light it is enough to pour one ¼ of the bucket into the electrical circuit per second. If you use the thickness planer you have to pour 5 buckets of 250 Volt every second into the electrical circuit. This is the electrical force. It is called ampere and the lamp needs ½ of one Ampere and the thickness planer needs 5 Ampere.
Ohm: - Ohm is the measurement of resistance, which occurs when electric energy is flowing. When we use the extension cord, you can feel that the extension cord gets warm. That happens because of the resistance. The same happens in a bulb. In a bulb there is a very thin wire. When electrical energy flows through this thin wire, it gets hot and gives off light. A lot off electrical energy would like to go through that thin wire, but because it is so thin, it provides high resistance and that resistance makes the wire hot
Figure
A fusebox consists of different fuses. At the mainswitch the power comes in and is distributed to the other fuses. Usually the light is secured with one 8 Ampere fuse and the powerpoints with two 15 Ampere fuses. The purpose of the fuse is to break the electrical circuit if it is overloaded. If an electrical circuit is overloaded for a long time the wires will melt and the house could easily catch fire. Make sure that the electrical circuit has the correct fuse.
The fuse itself can consist of wire which will melt and break the circuit. Once the fusewire is broken, replace it with the same thickness.
The other type of fuse is the bemetal fuse, which is getting more popular. This fuse has two special metal strips in it and when they become hot, they bend and break the circuit. Afterwards, when they cool down, you can switch the fuse on again. They are much easier to handle than the wire fuses.
Figure
a) Tools:
- Screwdriver
Figure
- De-sisalation pliers
Figure
- Combination pliers
Figure
b) Accessories:
- Bulb with Batten holder
Figure
- three core flex
Figure
- Connector
Figure
- Cable Clips
Figure
- Three pin plug
Figure
- Rocker switch
Figure
- Single powerpoint
Figure
- Fluorescent light
Figure
a) Light and switch: - The active line and the earth wire go to the switch and from there to the light. The neutral wire goes direct to the light. Make sure that the active line wire is connected in the right way at the switch. Strip back the insulation just enough to allow the bare wires to be clamped tightly under the head of terminal screws without pieces sticking out.
Figure
b) Powerpoint: - Usually at the back of the powerpoint it explains where to connect the wires. Just follow the instructions and tighten the terminal screws.
Figure
c) Three pin plug:- Make sure you connect the earth at the right terminal. For the active line and neutral wires it does not matter which pins you use.
Figure
d) Main earth wire: - Usually the main earth wire is connected to a metal rod driven into the ground.
Figure
You must start from the fusebox. The main active line wire is connected to the mainswitch in the fusebox. From there, the main active wire is distributed to three other fuses. One fuse is for the light and two fuses are for the power-points. A three core flex wire is distributed to the lights to make one electrical circuit and secured by one fuse. For the powerpoints you have to make two electrical circuits and secure them by two fuses. At the fusebox always connect the three core flex wire, earth to earth terminal, neutral to neutral terminal and active line to the fuse. The power-points usual mark where to connect the earth, neutral and active wire. At the light you have to be careful. Neutral and Earth are directly connected to the light, but Active has to go to the switch first and from there to the light. The earth from the switch is connected to the earth of the light.
Figure
With the alternate switch you are able to switch on or off the same light from different switches. For that kind of switching you need a special switch called an alternate switch. The terminals of this kind of switch are marked with C,1,2 and loop. C at the first switch is connected to the active wire (usually red coloured). In that terminal the power comes in. Now you take an other three core flex wire and connect the red wire of the new three core flex wire to 2 and earth to earth. This core flex wire has to go to the other switch and repeat the connecting: red to 1, black to 2 and earth to earth (marked with loop). Then the terminal screw at the switch, which is marked with C is connected with one wire to the light. The neutral from the light has to go to the neutral of the fusebox.
Figure
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