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Transcript
Engineering Skills: Electrical/Electronic – Intermediate 1 Answers Materials Number & Name Accessory Ferrous Non-ferrous Non-metallic 13A domestic plug top 5A one way switch Ceiling rose 13A switch socket Lamp holder One of the biggest disadvantages of ferrous materials is that they can rust or corrode and this is not really something you want in your lighting switch or lamp holder. Rust and/or corrosion will cause damage to the accessory and will eventually cause an open or short circuit. The table above shows that most of the electrical accessories that we use are made from a combination of non-ferrous and non-metallic materials. Even the switch and the switch socket fixing screws are made from an alloy that is nonferrous. Scottish Further Education Unit 1 Engineering Skills: Electrical/Electronic – Intermediate 1 Tools Screwdrivers There are several types of screwdrivers: Electricians’ Screwdrivers These normally have round blades with either parallel or flared tips. The handle is always made of an insulating material and the blade is often sheathed in plastic so that only the tip is exposed. Sometimes a neon indicator is incorporated into the handle as a safety device so that live voltage sources can be detected safely. The tip is slotted and is mainly used for connections in terminal strip, lighting switches and sockets. Slotted Screwdrivers Slotted screwdrivers are for use on slotted screws and have a flared tip on the end of a round or square section blade. They are available in lengths up to 450mm with tip widths of 10mm. Normally the wider the tip means a longer blade and larger handle. However special purpose screwdrivers are available with wide tips and short blades – these are usually called stumpy screwdrivers. Crosspoint Screwdrivers There are several types of crosshead screw in use, the most common of which are “Phillips” and “Pozidrive”. The screws are made so that the screwdriver is located securely into the head. It is important that the correct screwdriver is used with the relevant screw as the heads are easily damaged and can be particularly difficult to remove. Screwdrivers should not be used if the tip becomes damaged because it will not fit properly in the screw head. Screwdriver handles are normally made from wood or plastic. NB Scottish Further Education Unit Screwdrivers are NOT chisels. 2 Engineering Skills: Electrical/Electronic – Intermediate 1 Pliers Pliers are gripping tools that are used to hold components that would otherwise be difficult to hold and control. They are made from forged steel with hardened and tempered jaws to resist wear. There are six common types of pliers. Flat nosed pliers: Flat nosed pliers are basic pliers used for gripping and holding. Combination pliers: Combination pliers are more versatile than flat nosed pliers and incorporate side cutters (for cutting wire), a pipe grip and joint cutters. Electrical pliers: Electrical pliers are similar to combination pliers but with heavily insulated handles to withstand high voltages. Pin nosed pliers: Pin nosed pliers are more delicate than the heavier pliers and are used for holding or bending small components where access may be limited. Round nosed pliers: Round nosed pliers are used for holding, bending, securing and where access is limited. Pliers should never be used to tighten or undo nuts or bolts as the heads of the nuts etc will be damaged by rounding the corners. Scottish Further Education Unit 3 Engineering Skills: Electrical/Electronic – Intermediate 1 Multi-purpose Pliers – these include circlip pliers, wire strippers, side cutters: Side Cutting Pliers or Snips – are used a lot in electrical/electronic circuit construction to trim/cut cables. Snips should only be used to cut cables, copper wires etc. Wire Strippers (automatic) There are many types of wire strippers from those used for stripping single core to others for stripping twin and earth. Usually a wire stripper strips the insulation from the cable leaving the copper conductor exposed. The automatic strippers shown were also known as Yankee Strippers because of their origin. Wire Strippers Both types of wire strippers are a ‘cut and pull’ type of stripper. Electrician’s Knife In some instances a specially designed electrician’s knife may be used for stripping insulation. A ‘Stanley’ knife should never be used for this job as it has an extremely sharp blade. An electrician’s knife is usually quite blunt, to lessen the chance of damage to the copper conductor. Notice how blunt the knife is. Please note that this knife is a tool and as such would be kept in a tool box. It is an offence to carry a knife. Scottish Further Education Unit 4 Engineering Skills: Electrical/Electronic – Intermediate 1 Crimping Pliers Crimping is commonly used to clamp (crush in a way) terminals to cable ends. This gives the cable a robust connection that is both electrically and mechanically strong and long lasting. The crimped end can also be connected and reconnected many times without loss of mechanical strength and electrical conductivity. Scottish Further Education Unit 5 Engineering Skills: Electrical/Electronic – Intermediate 1 General Workshop Tools The following are the main hand tools you will find in all engineering workshops. Your instructor will show you how to use the tools and explain any special safety requirements. Saws A hand saw used to cut metal or plastic is known as a hacksaw and comes in various sizes, such as a junior hacksaw. The main type of hacksaw consists of a frame and a blade. The frame is adjustable to allow different sizes of blade to be inserted. The blade must be tensioned and inserted correctly. Blades are classified by the number of teeth per unit length. The greater the number of teeth the finer the cut. Normally thick materials are cut with a coarse blade and thin materials with a finer blade. When cutting, the whole length of the blade should be used. The hacksaw blade should never be used without the frame. Junior hacksaws are not adjustable and the blade is tensioned by the spring of the frame. The pad saw is different from hacksaws because it only has a handle and a blade. The blade is a narrow strip of steel which has cutting teeth on one side and this tool can be used in awkward or confined spaces. The pad saw might be used for cutting thin metal but more often it is used to cut shaped holes in wood or plasterboard. Footprints A ‘footprint’ is a gripping tool that can be adjusted to have a narrow or wide grip and is used to hold and turn metal conduit or couplings. It has serrated (grooved) jaws and will leave a noticeable mark if used wrongly. It gets its name from the trademark small ‘footprint’ symbol imprinted on each tool. Scottish Further Education Unit 6 Engineering Skills: Electrical/Electronic – Intermediate 1 Adjustable wrench Similar to a footprint, an adjustable wrench can be adjusted to different jaw sizes to grip and turn. This tool may also be found in a plumber’s tool kit and is sometimes called ‘water pump pliers’. Plumbers and electricians use them mainly to tighten decorative chrome or ‘bright’ metal fittings. Files A file is used to remove material from the work piece. Various types are available and can be used to complete a work piece accurately with a good finish. A file should never be used without a handle as the end of the file, or tang, is sharp. Flat File Scottish Further Education Unit Half-Round File 7 Engineering Skills: Electrical/Electronic – Intermediate 1 Hammers Hammers are important tools that must be used correctly and safely. They have a number of uses such as: shaping metal; driving things into position; tapping marking tools. Hammers are available in a wide range of weights from 200grams to 900grams. Bigger hammers are known as sledge and lump hammers and are used for heavy work. Hammer handles or shafts are usually made of wood but some are now made of plastic. These materials absorb the shock when striking. You should never strike one hammer with another as bits may chip off and damage your skin. When using a hammer you shouldn’t look at the hammer itself but at the end of what is being struck. This should help you not to hit your thumb! A mallet is a hammer in the loosest sense. This tool is used for the forming and shaping of sheet metal and is usually made from boxwood or hide. This allows metals with polished surfaces to be worked without undue surface damage. Mallets come in different forms depending on the use. Chisels Basic cold chisels are used in both engineering and construction to remove excess material or to split material. The bolster chisel is used by electricians to split floorboards along the tongue and groove to gain access under floors to wiring. In many cases now the modern electrician would simply use a quickcut. Scottish Further Education Unit 8 Engineering Skills: Electrical/Electronic – Intermediate 1 Activity: Tool Identification The table below shows you a selection of tools – fill in the table with what you think they are called. Tool Tool Picture Tool Name Tool 1 Tool 2 Tool 3 Tool 4 Tool 5 Tool 6 Scottish Further Education Unit 9 Engineering Skills: Electrical/Electronic – Intermediate 1 Answers Tool Identification Tool Tool Picture Tool Name Junior Hacksaw Tool 1 Electrician’s Screwdriver Tool 2 Tool 3 Cable Strippers Tool 4 Floorboard Chisel (Bolster) Tool 5 Side Cutters Snips Cable Cutters Tool 6 Combination Pliers Scottish Further Education Unit 10 Engineering Skills: Electrical/Electronic – Intermediate 1 Activity: Tool Su-Doku Each group of 6 boxes below must contain each of the listed tools, but also each line across and up and down must contain each of the 6 tools. Hammer Crimpers Scottish Further Education Unit Snips Pliers Strippers Screw driver 11 Engineering Skills: Electrical/Electronic – Intermediate 1 Answers Tool Su-Doku Hammer Crimpers Scottish Further Education Unit Snips Pliers Strippers Screw driver 12 Engineering Skills: Electrical/Electronic – Intermediate 1 Diagrams In electrical and electronic circuitry there are different types of diagrams: We will look at the following types of diagram: layout wiring circuit block. Layout Diagram Component Position These diagrams show the physical position of each component or circuit accessory. This type of diagram shows only the location of a switch or relay or resistor and does not show any interconnections or wiring details. This type of diagram is widely used in the installation of new circuits and in the maintenance and repair of circuits. SW 1 R4 R1 R2 R3 Tr1 Tr2 D1 D2 C1 C2 Wiring Diagram Cabling and Connections Wiring diagrams show the route the cabling or wiring actually takes and would possibly give the connection details as well. Wiring and layout diagrams are the most widely used for the installation of circuits whether it is for an aircraft, a motor car or a new house. Scottish Further Education Unit 13 Engineering Skills: Electrical/Electronic – Intermediate 1 Circuit Diagram How the Circuit Operates Circuit diagrams show all the components and interconnecting wiring without any details of cable routes or component positions. This is the most widely used diagram for fault finding and repair of circuits. Circuit diagrams show how the circuit operates without showing the physical layout. Block Diagram Supply Socket Socket Circuits in Block Form A block diagram is a simple diagram in which a circuit or system is split into simple blocks that are labelled with the function of the block. Wires Crossing/Connection Convention Wires Connected Scottish Further Education Unit Wires Crossing 14 Engineering Skills: Electrical/Electronic – Intermediate 1 Current – Voltage – Resistance The relationship between current, voltage and resistance is important to all electrical engineers. Current Voltage Resistance Symbol I V R Unit Ampere (A) Volt (V) Ohm (Ω) What exactly are voltage, current and resistance? This is a picture of the Hoover Dam. Current (symbol I) is like the water flowing from the overflow valve in the side of the dam. Voltage (V) can be likened to the pressure of water. The more water in the dam - the more pressure pushing water out. It’s the same with voltage: more voltage = more current. Resistance (R) in this case is the size of the opening of the overflow valve. If the valve is slightly open then the flow pressure would be high and if the valve is fully open the flow pressure would be lower. Apply this to an electrical circuit: Current (I) is what flows through a wire or conductor like water flowing out of the dam. Current flows from points of high voltage to points of low voltage through the conductor. Current is measured in amperes (A). Ampere is shortened to amp. Voltage (V) or sometimes (E) is the difference in electrical potential between two points in a circuit. It's the push or pressure behind the current flow through a circuit, and is measured in volts (V). Resistance (R) determines how much current will flow through a component. Resistors are used to control voltage and current levels. A very high resistance allows a small amount of current to flow. A very low resistance allows a large amount of current to flow. Resistance is measured in ohms (Ω). The relationship between V, I and R is stated in Ohm’s Law. Scottish Further Education Unit 15 Engineering Skills: Electrical/Electronic – Intermediate 1 Ohm’s Law Ohm’s law states that, in an electrical circuit the current (I) that flows is directly proportional to the voltage applied to the circuit. What this really means is that: If the voltage increases and If the voltage decreases the current increases the current decreases Georg Ohm Also if the voltage remains constant (this is what happens in most circuits) then the resistance and current are indirectly proportional. What this means is that: If the resistance decreases and If the resistance increases the current increases the current decreases Anyway, try this with some simple figures: If the voltage source remains constant at 100V look what happens to the current as the resistance increases: Voltage (V) 100V 100V 100V 100V Resistance (Ω) 1Ω 10 Ω 100 Ω 1000 Ω (1k Ω) Current (I) 100A 10A 1A 0.1A (100mA) The relationship between voltage, current, and resistance is given by a simple equation derived from Ohm’s Law. Fill in the blanks: V = IR V Voltage = Current x Resistance This will mean that: I= R Current = _________ ÷ ___________ and R= V I ______ = _________ ÷ ___________ Scottish Further Education Unit 16 Engineering Skills: Electrical/Electronic – Intermediate 1 Circuits In any circuit, if there is a source of energy and a load, a current will flow. This current flows through each component and this in turn creates a voltage drop across each component. Scottish Further Education Unit 17 Engineering Skills: Electrical/Electronic – Intermediate 1 Activity: Electrical Symbols and Units Complete the following table of electrical symbols and units Current Voltage Resistance Symbol Unit Ohm’s Law – Calculations Ohm’s law states that, in an electrical circuit the current (I) that flows is directly proportional to the voltage applied to the circuit. Complete the table by applying that relationship: Voltage (V) Resistance (Ω) 150V 150V 150V 150V 1Ω 10Ω 100Ω 1000Ω Current (I) (1kΩ) Remember the current = voltage divided by the resistance Remember to write the units. Scottish Further Education Unit 18 Engineering Skills: Electrical/Electronic – Intermediate 1 Answers Electrical Symbols and Units Current Voltage Resistance Symbol I V R Unit Ampere (A) Volt (V) Ohm(Ω) Ohm’s Law – Calculations Ohm’s law states that, in an electrical circuit the current (I) that flows is directly proportional to the voltage applied to the circuit. Complete the table by applying that relationship: Resistance (Ω) 1Ω 10Ω 100Ω 1000Ω (1kΩ) Voltage (V) 150V 150V 150V 150V Current (I) 150A 15A 1.5A 0.15A or 150mA Did you remember to write the units? Scottish Further Education Unit 19 Engineering Skills: Electrical/Electronic – Intermediate 1 Electrical Circuits Common Domestic Circuit Types Lighting The most common lighting circuits used in houses are one way lighting and two way lighting. One Way Lighting One way lighting is where a light is switched on and off by one switch only. A toilet usually is a common example of a one way lighting circuit. The switch is near to the door and is switched on in the way in, and switched off on the way out. Two way lighting Two way lighting is where a light can be switched on in one place and switched off in another place. A stairway is a common example of a two way lighting circuit. The light can be switched on at the bottom of the stairs and switched off at the top of the stairs or vice versa. Scottish Further Education Unit 20 Engineering Skills: Electrical/Electronic – Intermediate 1 Power Circuit Types Power circuits in the UK are normally radial or ring. Radial Circuit A radial circuit is where power is transmitted from the supply to the first socket then to the second, to the third etc and terminates at the last socket. Socket 1 Socket 2 Socket 3 Supply Radial Circuit Ring Circuit A ring circuit is where power is transmitted from the supply to each socket then is connected back to the supply. Socket 1 Socket 2 Supply Socket 3 Ring Circuit The ring circuit allows more power to be safely supplied to the circuit using the same cable size as a radial circuit. Scottish Further Education Unit 21 Engineering Skills: Electrical/Electronic – Intermediate 1 Circuit Tests There are many tests that will help us to check that the circuit does exactly what it is supposed to do and in a safe manner. If the circuit works but goes on fire after a short time then that is neither good nor safe! One of the most basic tests that electrical/electronic engineers carry out on a circuit is the continuity test. Continuity Test A continuity test checks the circuit to see that the circuit is a complete loop. A continuity tester can be: a meter that gives a reading audible like a high pitched sound, or a simple test lamp. A good continuity test shows that the conductors are not broken and that all the connections are at least reasonable. However, a continuity test, although useful, is not enough to show that the circuit is totally safe so it would usually be used with other tests. switch Continuity tester light lights or makes sound In this case the circuit is good and the continuity tester lights or makes a sound. Scottish Further Education Unit 22 Engineering Skills: Electrical/Electronic – Intermediate 1 switch Continuity tester light does not light or make sound bad connection at light fitting In this case the circuit is not good and the continuity tester does not light or make a sound. The other useful task that a continuity test can do is to find the end of each cable if you have a bundle of wires all the same colour. Circuits Activity Circuits can be more than just electrical circuits, so for this activity you must try to list 4 circuits. Let’s start with a 400 metre athletics track. 1. 400 metre athletics track 2. 3. 4. Hint - Think continuous circles! Scottish Further Education Unit 23 Engineering Skills: Electrical/Electronic – Intermediate 1 Answers Circuits Activity You might have thought of some of these: 1. 400 metre athletics track 2. Satellite orbit of the earth 3. Doughnut (jam ones don’t count) 4. Roller coaster ride 5. Go-kart racing track 6. Bicycle wheel etc. Scottish Further Education Unit 24 Engineering Skills: Electrical/Electronic – Intermediate 1 Electrical Wires and Cables Electrical wires and cables come in many forms and sizes and have a variety of uses. Wires are solid or stranded, insulated or un-insulated conductors. For most applications, the main requirement of a cable is that it should carry a specified electric current between two points in the most economical way. This means we’re looking for a material that offers little resistance to the passage of electricity to minimise energy loss along the cable length. Silver is one of the best materials, but it cannot be used because it is too expensive. Copper is the most suitable in terms of carrying current and cost – it’s cheaper! Aluminium, which is not as expensive as copper needs a larger size of conductor to carry the same current – so it works out to be more expensive in the end. Aluminium scores over copper mainly in weight saving, because it is lighter than copper. In the UK, aluminium conductors are usually only used for large fixed-installation power cables for electricity distribution. Although most wires are made of copper, it is worth remembering most metals will conduct electricity. Cables are insulated wires contained within an outer insulation or sheathing. Cable Insulation To prevent danger from electric shock and possible short-circuits, wires and cables are covered in an insulating material. In most cases, the cables used in this unit will be insulated with PVC. polyvinyl chloride (PVC) – clean, easy to use, cheap and resistant to corrosion. This is the most widely used. rubber – very cheap but prone to perishing polytetrafluoroethylene (PTFE) – expensive but able to withstand high temperatures. Scottish Further Education Unit 25 Engineering Skills: Electrical/Electronic – Intermediate 1 Wires and cables have many uses, for example: electrical installations (ring mains, lighting) flexible mains (kettle, vacuum cleaner) data transmission (telephone, computer, TV). The selection of the electrical cable is dependant on the following factors: Cable Use Cable Current Cable Voltage Cable Situation Some of these are shown in the table below: Cable Use Motor Car could be for………… Current that might flow House Wiring Small Kitchen Appliance Large could be…………… Voltage that will be applied Low High could be …………………. Situation Temperature Vibration Environment choice of cable might depend on……………….. This means that the type of electrical cable used in a motor car would not be the same as the type of cable that would be used in the washing machine even though both cables carry the same current - but not at the same voltage. A co-axial cable that is used to connect the signal to the television is very different from the electrical cable used to connect power to the kettle. Scottish Further Education Unit 26 Engineering Skills: Electrical/Electronic – Intermediate 1 Current Colour Codes Single Phase: Protective earth (PE) Green/yellow striped Neutral (N) Blue Live (L) Brown Wire types Single strand wire This type is used where rigidity is required or flexibility is not required. It can be bent, but must not be used in applications where it will be flexed frequently because this would cause it to break. Multi-strand wire Multi-strand is used where a flexible bend in the wire is required. It is classified by the number of strands in the wire and the diameter (in mm) of each strand. The difference is not only the voltage or current rating of the wire but also the vibration and movement of the wire. Scottish Further Education Unit 27 Engineering Skills: Electrical/Electronic – Intermediate 1 Cable Types Power Cables Mains voltage is usually 230Volt in the UK and power cables are designed to carry mains voltages and currents. Mains Cables Two-core and three-core power cables – usually called mains cables – are used to connect appliances to the public mains supply via a 13A plug and socket. Two-core cables have wires coloured brown (for live) and blue (for neutral). Three-core cables have an additional green/yellow wire (for earth). Since mains cables are normally subject to a lot of flexing and movement they tend to be made up of stranded conductors rather than a solid conductor. There is no vibration or movement in house wiring so single core, single conductor can be used but usually it would be twin and earth. Scottish Further Education Unit 28 Engineering Skills: Electrical/Electronic – Intermediate 1 Signal cables Signal cables consist of one or more conductors surrounded by a screen. The screen is braided copper running the complete length of the cable. It is used to isolate or screen the signal in the central conductor(s) from any outside interference. It also provides security because the screen prevents any radiation from the inner signal. Multi-core screened cable Coaxial cable Coaxial cable is a screened cable with a single solid or stranded conductor surrounded by layers of insulation and screening. Coaxial cable is used to connect an aerial to the input of a television, and also as connecting leads for test instruments such as oscilloscopes and signal generators. Coaxial cable Ribbon cable Ribbon cable consists of a number of single-core stranded wires joined together lengthways in the form of a flat ribbon. Ribbon cable provides a quick, simple and cost-effective solution to mass termination. It also has space and weight-saving advantages over other wiring methods. It is ideal for use on computers, peripherals, interfaces, audio and digital equipment. Coloured 10-way ribbon cable Not all ribbon cable is multi-coloured. Scottish Further Education Unit 29 Engineering Skills: Electrical/Electronic – Intermediate 1 Cable Types and Crimped Terminals Type Picture Use PVC insulated cables sometimes called Twin and Earth Mainly domestic and commercial premises. Used for lighting circuits and power circuits. Single Core (multi-stranded) Industrial use for circuits where the wiring is subjected to vibration or movement. Various colours Domestic and commercial uses to connect appliances such as: computers, kettles, X-boxes. The 2-core version has both its core insulation and its outer sheath made of PVC. Domestic and commercial use to connect signals to television. Multi-core Flexible Cord 3 Core Multi-core Flexible Cord 2 Core Coaxial Crimp Ring Many applications: Aerospace Crimp Spade Automobiles Crimp Domestic Appliances Receptacle Female Male Scottish Further Education Unit 30