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Contents Introduction Assessment criteria 2 2 Parts of a cable 4 Electrical cable types 5 Sheathed and unsheathed cable 5 Flat and circular sheathed cable 5 Number of cores 6 Sheathing colours 6 Special cable types 7 Cable design Conductor stranding 9 9 Common cable configurations 10 Cable insulation 11 Cable identification 12 Conductor colours 12 Applications of cables 14 Fixing and supporting sheathed cables 14 Limitations on use of sheathed cables 15 Insulated cables without sheath 15 Jointing and terminating cables 16 Soldering 16 Terminal blocks 17 Crimped connections 17 Poor connections 18 Summary 20 Answers 23 EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 1 Introduction All electrical circuits consist of cables of one type or another. You must be able to identify the types of cables you are expected to use, so that you can select the correct cable for the particular application. In this section, we’ll look at the types of insulated cables used for electrical wiring, identification of cables, termination of cables, and accessories. Sheathed cable is the most commonly used cable in electrical installation work. It is used almost exclusively in domestic installations, very widely in wiring in commercial buildings and extensively in industrial wiring. Sheathed cable is made from cores of building wire enclosed by another material. Assessment criteria At the end of this section you should be able to: list common cables and state typical applications explain the terms conductor material, stranding, insulation type, voltage rating, screening, sheathing, armour and serving state the Australian and International colour standards for cords and cables describe the construction of common cables identify cords and cables by conductor size, type and rating describe typical applications for given cord and cable types identify hardware used in terminating cords and cables demonstrate correct preparation for termination of cords and cables correctly terminate cords and cables using crimp lugs, tunnel connectors, soldering and solderless lugs 2 EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 Resources You will need the following resources to complete this section. All resources should be available from your campus bookstore: AS/NZS 3000:2000 Electrical Installations: Australia and New Zealand. We will refer to this Standard as ‘the wiring rules’. Electrical Wiring Practice by Pethebridge and Neeson. We will refer to this reference in the text as EWP. The resource manual for this module (with a yellow cover). EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 3 Parts of a cable You need to be familiar with the terms describing cables that are used in the wiring rules. These terms include the following: Term Meaning Armour Armoured cables are use in environments where the cable must be protected from mechanical stress. These cables have a layer of steel wire just beneath the serving. Conductor The metallic, conductive material that performs the main function of the cable. May include the insulation, depending upon the context. Core One of the insulated conductors in a cable Insulation Each conductor is surrounded by a layer of insulation of polymer material such as PVC or polyethylene, preventing electrical contact between the conductors. The sheath also a acts as further insulation between conductors in different cables, or between a cable conductor and an earthed enclosure for example. Serving The final sheath forming the outer surface of the cable. Sheath A part that surrounds and protects the cores of the cable. May be of polymer like PVC or metal such as lead or steel. In common sheathed cable for general use, the sheath is typically PVC. Some underground or undersea cables may have inner sheath. Shielding A conductive layer of metal tape or braid which prevents electric fields and electromagnetic interference from leaving or entering the cable. Strands A conductor may be composed of multiple strands of wire, to improve the flexibility of the cable. See EWP Figures 4.6, 4.7 and 4.8 for illustration of these terms. 4 EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 Electrical cable types Sheathed and unsheathed cable The vast majority of installed cable is sheathed – in other words, it has a sheath or outer wrapping. Sheathed cable consists of conductors surrounded by thermoplastic insulation, and then surrounded again by a protective outer sheath, normally made of polyvinyl chloride (PVC). This type of cable is commonly called TPS (thermoplastic sheathed) cable. The sheathing provides protection for the single-insulated cores inside the cable. Where it is installed in a position that is not subject to mechanical damage (as defined by the wiring rules), no further protection is required. Unsheathed cable is just the insulated conductor, essentially identical to one core of a sheathed cable. The wiring rules refers to unsheathed cable as ‘insulated cables (without sheath)’, but common unsheathed cable is known in the trade as building wire, or TPI (thermoplastic insulated) cable. In most situations unsheathed cable must be installed within an enclosure (eg conduit), so it is less commonly used. Flat and circular sheathed cable Sheathed cable can be made in flat or circular configuration. Flat cable has these characteristics: it is less expensive, because additional filler material is required to make a circular cable, it is easy to attach to building structures such as rafters and studs, it becomes increasingly difficult to handle as the conductor cross sectional area (CSA) increases. For these reasons, flat cable is typically used in residential installations, where low cost and ease of installation are important, and where lower amperage circuits are the norm. Circular cable has the following characteristics: EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 5 is easier to install, especially in the larger sizes, because twisting is not a problem is more expensive it is easier to handle, especially when a large CSA is required is a natural shape for cables that require more than three cores, such as those for three phase circuits or communications and instrumentation circuits. is a natural shape for the manufacture of special cables such as high temperature cable, and armoured cable. For these reasons, circular cable is used extensively in industrial or commercial applications, where cable trays or cable cleats are required, and where heavy currents and three phase circuits are common. Note that single core sheathed cable, or unsheathed cable is naturally circular anyway. Multi-cored circular sheathed cables are available in a wide variety of sizes. In 3-phase multi-core cables rated greater than 200 amps per phase, the neutral core may be reduced in size to as small as half that of the active cores. Cables of this type are referred to as 3 12 core TPS cable. Number of cores Sheathed cable may have only one core or a number of cores. There are common names applied to the various configurations. When the sheathed cable has only one core it is referred to as single double-insulated (SDI) cable. Two core sheathed cable is referred to as twin sheathed cable, or just ‘twin’. A cable containing cores for active, neutral and earth is called twin and earth sheathed cable or just ‘twin and earth’. Cable is also made in three and four cores, both with or without an earthing conductor. Sheathing colours The most common sheathing colour for domestic applications is white. White cable can be easily coloured with water-base paint if it is in an exposed position. It also allows it to be more easily seen in places where there is little light (for example, ceiling spaces). Other standard sheathing 6 EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 colours are black and grey and many electricians prefer these for surface wiring where appearance is important. The standard industrial electrical colour is orange and some industries do not allow other sheath colours. Circular cable is therefore almost always orange in colour. Flat sheathed cable can also be purchased with orange sheathing. A red sheath is used almost exclusively for fire alarm systems in buildings so that cables are not confused with low-voltage wiring. Another example is the use of blue sheathed cables for instrumentation wiring. In a large installation, several sheath colours may be used. Distinctive sheathing colours makes for easy identification and reduces the possibility of wrong connections to a specific type of circuit. Caution Two sheath colours which cannot be used are those reserved for earthing conductors (that is, green, yellow and green/yellow). However, if a single core double-insulated (SDI) cable is used as an earthing conductor, you must use the green/yellow combination for the sheath. Special cable types We have only discussed cables for low voltage installations, and for general use. There are many other types of cables for use in different fields such as communications, for arduous conditions or special applications such as mining, undersea, or use in high temperatures, and for high voltages. EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 7 Student exercise 1 1 What is one desirable feature of wiring with sheathed cable? ____________________________________________________________________ 2 What is sheathed cable with one core often called? ____________________________________________________________________ 3 What two configurations are sheathed cables made in? ____________________________________________________________________ 4 What specific use is made for cables with the sheath colours of: (a) red? ____________________________________________________________ (b) blue? ___________________________________________________________ Check your answers with those given at the end of the section. 8 EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 Cable design Conductor stranding As you know, current passing through a conductor causes heating, energy loss, and a voltage drop across the conductor. Ideally, we would use conductors with zero resistance, but this is not possible with today’s technology. Instead, we must compensate for these effects by increasing the cross sectional area of the conductor as the required current increases. The ability of a cable to carry current, without overheating, is termed its current carrying capacity. The more current a cable must carry, the larger we must make the cross sectional area of the conductors. You will learn how to select cables later in your course, but here we will look at the practical implications for cable manufacture. If we use a solid conductor, the cable will become very stiff as we increase the cross sectional area, and will become unmanageable. To avoid this, the cable cores are stranded: a core can be comprised of many fine wires wound together. A cable of 1 mm2 CSA is always a solid single conductor, and those of 1.5 mm2 and 2.5 mm2 can be either solid or stranded. All other sizes are stranded. The number of strands in cores of increasing CSA follows a definite pattern. This pattern is: 1, 7, 19, 37, 61 and 127. Referring to Figure 4.4 in EWP, you will see how these numbers arise. They are simply determined by the number of strands that will fit neatly around the previous layer. As the cable core is created, each successive layer of strands (each ply) is wrapped in opposite direction. This helical wrapping keeps the cable together once it has been made. After all the layers have been applied, the cable is covered with thermoplastic insulation. Standing is specified as two numbers separated by a slash (/). The first number is the number of strands and the second is the diameter of each strand in millimetres. For example, a cable marked as 7/0.67 has 7 strands of EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 9 wire, each 0.67 mm in diameter. Table 1 shows a sample of conductors and how they are constructed. Table 1: Stranding of conductors No of strands Dia of strands (mm) Cross-sectional area 2 (mm ) 1 1.13 1 1 1.38 1.5 7 0.67 2.5 7 1.35 10 19 1.35 25 19 1.78 50 37 2.03 120 Common cable configurations The main types of flat sheathed cable that are made as standard items are shown in Table 1. Table 1: Sheathed cable construction No of strands Diam of strands (mm) Crosssectional area (mm2) No of cores in cable 7 0.50 1.5 2 core + earth flat 7 0.67 2.5 4 core + earth 19 1.35 25 4 core 7 1.35 10 3 core + earth circular 19 1.53 35 1 core 37 2.52 185 1 core 19 1.53 35 4 core + earth circular + 3 12 + earth circular 7 0.50 1.5 2 core There is a practical limit to the conductor size for multi-core sheathed cables because the multi-core types become too heavy and awkward to handle. In addition, practical considerations are such that flat cables of more than four cores and earth are not made. More cores can be fitted in the circular 10 EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 configuration, but it is rare for any stock cable to contain more than four cores and earth. See EWP Figure 4.10 for some commonly used flat cable types used for general wiring. Some general information on accepted installation methods and cable sizes is given in Tables 3.1, 3.2 and 3.4 of the wiring rules. Installation electricians must select the correct size cable both for the current it will carry and its location. This information may be found in the AS/NZS 3008.1 series Visit a cable manufacturer’s website for a catalogue of common cable types. For example, visit www.olex.com.au and follow the links to products/low voltage. Then click on the link to the current product handbook. Cable insulation The properties of the insulation largely determine how a cable can be used. The electrical properties of the insulation include its dielectric strength and breakdown voltage. These will determine the maximum voltage of the cable for example. There are many other important properties including the strength, thermal conductivity, resistance to chemical attack and so on. One important property is the resistance to elevated temperatures. Whenever there is a current in a cable, heat is produced. This heat cannot be so high that the cable insulation begins to sag or ages prematurely. Different grades of insulation will withstand different temperatures. Normal thermoplastic (such as polyvinyl chloride PVC) insulated cables operate at a maximum temperature of 75C. Other PVC cables, under certain conditions, may be operated at 90C and 105C. Other special cables with fibrous insulation may be operated to 200C or higher. Read EWP section 4.3 for a treatment of cable insulation and sheathing materials for high or low temperature, fire resistance, pest resistance and chemical resistance. EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 11 Cable identification Sheathed cable is identified by a label on the cable drum. This label gives information about the: manufacturer number of cores core csa strands in each core size of the strands in each core colour of the sheath voltage and temperature rating. A typical label is shown below in Figure 1. ABC CABLE COMPANY Twin and earth flat 1.5 mm2 stranded (7/0.50) 0.6/1 kV 75°C White PVC/PVC Figure 1: Typical label on a drum of sheathed cable Conductor colours In Section 3 of AS/NZS 3000:2000 the first entry concerning colour codes is Clause 3.8.1 (page 87). Let’s look in detail at this part of AS/NZS 3000:2000. Table 3.5 lists acceptable colours for active, neutral and earthing conductors. 12 EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 Earthing conductors Green/yellow is the recommended colour for earthing conductors. This combination was chosen because people who are mildly colour blind have difficulty in separating red and green colours. Clause 3.8.1 requires that where a combination (eg green and yellow) is used, each colour must cover at least 30% of the surface area. Note that in general practice the colour violet (or purple) is not used for any low-voltage conductor as it identifies telecommunication cables. Most electricians prefer to use a distinguishing colour for switch wires when carrying out wiring work. These are conductors which are made active when a switch is turned on. A common colour for these conductors is white. By using this colour in single-phase wiring, there is little chance it can be confused with the red active when making connections at lights. This is not stated in AS/NZS 3000:2000 but is good working practice. See EWP section 4.4 for a discussion of the identification for fixed wiring and flexible cables. Student exercise 2 1 What clause in AS/NZS 3000:2000 applies to sheathed cables buried in the ground? ____________________________________________________________________ 2 What happens when sheathed cables are exposed to very high temperatures? ____________________________________________________________________ 3 What clause in AS/NZS 3000:2000 deals with fixing sheathed cable? ____________________________________________________________________ Check your answers with those given at the end of the section. EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 13 Applications of cables Probably more sheathed cables are used than any other type of wiring system since it is practically the only type of wiring used in domestic installations. In timber-frame buildings, the cable can be run in wall cavities, frames and ceiling spaces without further enclosure. This makes sheathed cable very quick and easy to install. Sheathed cables are used extensively in commercial installations for the wiring of lighting and GPO circuits. They can be taped together in looms and laid above suspended ceilings, which is much quicker than wiring in conduit and building wire. In industrial applications, sheathed cable can be used in areas where it is not subject to damage. One application is the wiring of lights on roof trusses, and also for cable tray and cleat wiring. Sheathed cable is considered to be a wiring enclosure and is far easier to install than cables in conduit. In addition, it may be buried directly in the ground as long as clause 3.11.3.2 of the wiring rules is strictly followed. Sheathed cable is also widely used in the installation of catenary wiring systems complying with clause 3.13 of AS/NZS 3000:2000. Fixing and supporting sheathed cables Sheathed cables are to be fixed and supported in accordance with the requirements of clause 3.9.3 of AS/NZS 3000:2000. The point to remember is that sheathed cable must be fixed in place with suitable clips. Clause 3.9.5.3 of AS/NZS 3000:2000 requires that cables likely to be disturbed (as indicated in clause 3.9.5.2 of AS/NZS 3000:2000) are to be fixed to prevent undue sagging. 14 EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 Limitations on use of sheathed cables Sheathed cable is a most useful and versatile wiring system. However, it is liable to damage by severe mechanical forces or high ambient temperatures. High temperatures can cause the plasticiser in the sheath to evaporate and leave the cable rigid and brittle. Sheathed cables are not used where solvents could affect the sheath, as solvents will cause similar problems. Insulated cables without sheath We have mentioned that standard unsheathed cable (building wire) can be used in conduits for some situations. However there are other types of unsheathed cable with specific applications, including: • single insulated flexible cables often used for wiring within appliances. • glass fibre insulated cables used for high temperature situations such as ovens. The insulation is fragile and could be damaged when pulled through conduits. Again, they are more expensive; • telephone cable or bell wire which has insulation only suitable for extralow voltage; • instrument or data cable only suitable for extra-low voltage; • insulated aerials conductors are not annealed and so are too stiff and hard to draw into conduit. None of these cable types is suitable for general purpose, low voltage installation wiring. EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 15 Jointing and terminating cables All electrical cables must be connected to a circuit in some manner. This connection is called the termination of the cable. There are many ways in which a cable can be terminated including the use of connectors, soldering, crimping, compression fittings and equipment terminals of many types. The termination of a cable depends on the type of cable, its application and its size. We will have a look at a number of terminating methods in this section. Three basic factors to consider when terminating a cable include the following: The connection must be good electrically, which means it should have as low a resistance as possible. The connection must be good mechanically. There must be no undue mechanical stress on the connection, and the connection must not loosen due to vibration or thermal cycling. A connection should not interrupt the insulation any further than is necessary to make the connection. First let’s see what AS/NZS 3000:2000 has to say on the subject of terminations. Clause 3.7.2.2 deals with the removal of insulation from the cable. There are special conditions mentioned, such as: the insulation shall not be removed any more than necessary, the connection shall be insulated and damaged insulation replaced. Clause 3.7.2 of AS/NZS 3000:2000 covers connection methods. Whatever method is used, it must provide electrical continuity and adequate mechanical strength. Soldering Soldering is covered in AS/NZS 3000:2000 by clause 3.7.2.6. It should be observed that if flexible cords are soldered, care must be taken to prevent the solder running up the flexible conductor by capillary action. 16 EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 This solder flow makes the flexible core stiff and if it is flexed at this point, it could break off. Another requirement in soldering is that corrosive fluxes must not be used. A corrosive flux (eg hydrochloric acid) acts as an excellent flux but will continue to corrode the conductors long after the joint has been made. It could also damage enclosures or equipment. Terminal blocks Cables are commonly terminated in terminal blocks. These come in many varieties of size, number of cables accommodated, current rating, terminal layout and screw thread types. There are many hundreds of varieties and the only way to find a suitable type is to consult a manufacturer’s catalogue. Crimped connections Crimping should only be done by a tool specially designed for the job using a size suitable for the cable and by using a crimping sleeve or lug specially made for the cable size. Crimp connections are made using a wide variety of lugs, including: those with holes, or eyes, for slipping over terminal screws slotted ends for pushing under terminal screws quick connect table ends quick connect bullet terminals (as used in automotive and some appliance wiring). Compression joints or terminations are usually only done on cables from about 10 mm2 or more. The compression type of termination is made by squeezing the surrounding sleeve and the cable from all sides to remove practically all internal spaces. A completed compression joint is basically solid copper. Connection of cables by connectors is usually limited to connecting cables in junction boxes. Connectors of the normal type (tunnel terminals surrounded by insulating material) are usually limited to cable sizes up to 6 mm2. When joining earthing conductors with tunnel connectors, the tunnel connector must have two screws (Clause 3.7.2.10 of AS/NZS 3000:2000). Another common termination procedure is to use solderless lugs. The cable core is made into a small circle, and the lug is slipped over the cable end and the lug is secured to the cable, usually with pliers. It is common practice to use solderless lugs for terminating earthing cables. EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 17 Poor connections When terminating cables the colour coding of the cables must be maintained. It would be a disastrous error to mistakenly connect an earthing conductor to an active terminal. A licensed electrician could be charged with manslaughter if this incorrect connection resulted in someone’s death. High resistance joints can result from any of the following: poor soldering poor crimping or compression loose screws loose nuts. All of the above problems are due to poor working habits and the electrician must use the correct procedure for each connection. The effect of a poor connection is not normally detected when the current passing through the connection is small relative to the capacity of the circuit conductor. It is usually when the rated load current through a conductor is required that the effect of a poor connection is detected. The high resistance joint between the contact surfaces at the termination passes the same current as the circuit conductors. Since the heat produced in a conductor is proportional to the resistance through which the current passes, the high resistance joint will produce a localised ‘heat spot’. Heat spots may be detected as abnormally high temperatures by thermographic photography or visual signs of insulation ‘browning’ or burning. If a condition like this is not detected the surface connection at the termination will deteriorate leading to an even higher resistance joint and therefore a higher temperature. The likelihood of a fire igniting the cable insulation is great. When power cables are terminated it is essential that the contact surfaces of the connecting surfaces be made secure and flush. Under-tightening or overtightening of a bolt connecting the two surfaces of a cable termination may lead to poor surface connection where the cross sectional area of the conductor is not maintained through the termination. Some suppliers of electrical equipment may specify a particular torque setting for tightening bolts so that correct tension is achieved at the contact surfaces. See EWP sections 4.6 to 4.8 for information on joining and terminating cables. 18 EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 You will learn more about making terminations in your practical sessions, and on the job. Student exercise 3 1 What part of AS/NZS 3000:2000 covers soldered joints? _____________________________________________________________________ 2 Where are solderless lugs commonly used? _____________________________________________________________________ 3 What can be the result of a high resistance joint? _____________________________________________________________________ Check your answers with those given at the end of the section. EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 19 Summary In this section you have accomplished the following outcomes. During your practical session some of these outcomes will be reinforced. Sheathed cables are a double-insulated wiring system and need not be enclosed further, if not subject to damage. Sheathed cables are made in flat and circular configuration. Flat cable is only available in smaller sizes, and cores of three or less. Circular sheathed cables are made in large sizes with up to 30 cores for special applications. Sheath colours vary, but the most common colours are white and black. The industrial sheath colour is orange, while red is reserved for fire, and blue for instrumentation. Sheathed cables are used extensively in domestic wiring, and also in commercial and industrial wiring.. Sheathed cabled are liable to be damaged by severe mechanical forces or high ambient temperatures. Building wire is single insulated thermoplastic cable for use in lowvoltage wiring. Building wire is suitable for voltages of 600 volts to earth and 1000 volts between conductors. 1.5 mm2 and 2.5 mm2 building wire can be either solid or stranded. Building wire must be installed in enclosures. Enclosures can be conduit, duct or troughing. PVC conduit is made of medium duty and heavy-duty types. The labels on cable drums or reels give the length, size, stranding, voltage rating and maximum operating temperature of the cable on the drum. All earthing conductors must be either green or green/yellow combination. All neutral conductors should be black. 20 Active conductors may be any colour except the colours reserved for earthing and neutral. EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 The conductivity of a joint must be no less than the cable itself or, in other words, the resistance must be no higher than the same section of cable. The insulating properties of joined cables must be maintained. Loose tunnel-type connectors for earthing conductors must have two screws. Earthing conductors are often terminated with solderless lugs. Colour coding must be maintained when connecting cables. High-resistance joints can lead to overheating of the cable termination. Cables may be terminated by: – – – – – connectors soldering crimping compression using terminals. Quick-release spade and bullet connections are used in automotive and appliance wiring. Connectors are used for joining fixed wiring cables up to 6 mm2 in junction boxes. Crimping is normally applied to lugs used on cables to small power equipment termination or control equipment terminations (ie Stop/Start push buttons, PLC’s etc.) Compression connections are usually made to cable lugs that connect into medium to large motor terminal boxes. The lug that is compressed normally has a hole in the flat palm that is slipped over the terminal screw before being fastened. The correct size crimp lug and crimping tool must be used for crimped joints. A good termination is as important as the cable itself. Some ways of mounting accessories to masonry surfaces (bricks, concrete) are by screwing into wall plugs, using nail in plugs or masonry anchors, or using an explosive powered tool in conjunction with specially designed fixings. EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 21 To drill a hole in masonry, a tungsten carbide tipped drill bit is often used and when using the power drill, it should be set to its percussion/hammer function. Cable clips are used to fix TPS cables to surfaces, whereas saddles are used to fix conduits. If an explosive tools is to be used you must first be trained and given a certificate of proficiency. There are many accessories used in the electrical industry and in order that engineers, salespeople and tradespersons can work efficiently, we must be able to identify the most common items used. Check your progress Now that you have worked your way through this section, it is time to have a look at your module workbook (in the yellow folder), at the appropriate section. Attempt the review questions now in the same way as you have been doing the student exercises. The answers are at the back of your workbook. Yours teacher at the practical session will check the work you have done and help with any problems. 22 EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 Answers Student exercise 1 1 It can be done quickly; it’s cheaper. 2 SDI (single double-insulated) 3 flat and circular 4 (a) fire alarms (b) instrumentation wiring Student exercise 2 1 Clause 3.11.3.2 2 The cable could lose its plasticiser and become very brittle. (Heat also softens PVC and that could also cause problems if there is any strain on the cable.) 3 Clause 3.9.3 Student exercise 3 1 Clause 3.7.2.6 2 connecting earthing conductors 3 heating at the joint (it could glow red hot!) EGG221A: 3 Identify and terminate cables NSW DET 2017 2006/060/05/2017 LRR 5168 23