OVERVIEW OF ELECTRICAL

CABLES AND JOINTING (EVJ)

Learner Guide

TABLE OF CONTENTS ELECTRICAL CABLES AND JOINTING (EVJ) AIMS AND OBJECTIVES PAGE 1 LEARNING PROCEDURE PAGE 2 PART ONE : GENERAL CABLES OVERVIEW PAGE 3 PART TWO : CABLE END PREPARATION PAGE 4 SELF CHECK EVALUATION PAGE 5 PART ONE : RESOURCE NOTES PAGE 6 PART TWO : RESOURCE NOTES PAGE 8

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AIMS AND OBJECTIVES OF THIS PROGRAMME The primary purpose of this programme is to serve as a starting point for new trainees on the subject of cable jointing and terminal end preparation. This programme therefore should proceed other Tech AV programmes, namely the L. V.J. (Low Voltage) and M.V.J. (Medium Voltage) series. It must be noted that all procedures and tasks illustrated are typical but not necessarily preferred by every regulatory authority or particular organisation. The underlying "message" to all who partake in this series is that of safety and the creation of a safe electrical joint or termination. Much attention is given to details and procedures, which on the surface may seem "obvious". We believe however that when one is working on devices that carry "killer" voltages all detail is important. When you have successfully completed this programme you will be able to: 1. Describe the construction of basic cable types. 2. Prepare S.W.A. cable ends for purposes or termination, glanding and jointing.

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LEARNING PROCEDURE ABOUT THE VIDEO PROGRAMME The video programme is divided into two sections: o Part One describes the "what and why" of cables in a general overview. o Part Two demonstrates a typical procedure for preparing a steel wire armoured cable-end in order to fit a gland or effect a joint. THE GENERAL PROCEDURE FOR LEARNING o It is suggested that you begin by viewing the video (ECO-1) from start to finish and then re-wind the tape. This will give you a general "feel" for the subject. o Next, follow the instructions on the relevant learning guide, which appear on the following pages. o When you have satisfied yourself that you fully understand the subject you should perform the suggested assignment under the supervision of your Instructor or Tutor in your practical training area. o Your Instructor may decide to ~your knowledge and skills before allowing you to proceed with further cable programmes. o Resource notes are included for your reference after you have finished your general training. SAFETY Under no circumstance will you be permitted to work on live electrical apparatus. Work only on cables that have been allocated to you by your Instructor.

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PART ONE: GENERAL CABLE OVERVIEW INSTRUCTIONS View the video up to the "Review" break and then stop the video. ASSIGNMENT With the permission of the relevant person in charge: o Proceed to your cable store and see what cable types your company keeps on hand. o Look for manufacturers brochures on cable types and specifications. Study these and try to learn as much as you can about each type, for example:

What purpose they are for? What sizes and rating they are? What insulative construction they have?

o Look around your plant / factory / work area and observe all the places where cables are routed and see if you can identify types shown in the video programme. o Ask your Instructor or other qualified person to take you and show you any electrical sub-station or incoming supply lines that feed your plant / factory or premises. o Take note of things such as:

How cables are routed? How cables are secured into apparatus? Any safety notices, warnings and regulations.

When you have completed with this assignment proceed with the viewing of the video.

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PART TWO: CABLE END PREPARATION INSTRUCTIONS o Watch the second section of the video which demonstrates a typical procedure for preparing a cable end. o Pay attention to all detail and listen carefully to the narrator. ASSIGNMENT o When you have finished viewing the demonstration (and remember, you may view it more than once if you need to) then rewind the tape and hand it back to your Instructor. o Next, ask your Instructor to allow you to practice the preparation of S.W.A. cable in your work area. o When you have completed practising the task of cable-end preparation on a section of S.WA cable turn the page and assess your performance by completing the "Self Check".

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SELF CHECK EVALUATION

INSTRUCTIONS o Place a tick (√) in the relevant "Yes" or "No" column against the criteria mentioned. o Have your instructor check your assessment.

1. CRITERIA DESCRIPTION / COMPLETED JOB YES NO

o

o

o

o

o

Appearance of completed work neat.

All dimensions (i.e. cut backs) are to specification.

Conductor insulation is undamaged by cutting knife.

Tail lengths are sufficient.

Conductor ends bared sufficiently.

2. CRITERIA / TASK PERFORMANCE YES NO

o

o

o

Use of sharp knife was done in safe manner.

Hacksaw used to only partially cut S.W.A.

Bared conductor ends without breaking any strands.

WORK AND PERFORMANCE CHECKED BY: INSTRUCTOR/TUTO: ___________________________________________________________ DATE: _______________________________________________________________________ Upon completion of this programme please proceed with any other cable programme (LVJ OR MVJ series) of your, or your instructor's selection.

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RESOURCE NOTES PART ONE: A GENERAL OVERVIEW OF CABLES

CONDUCTIVE MATERIALS Copper, drawn into strands or into solid cores is by far the most commercially viable conductor material. Aluminium is however used extensively owing to its lower cost. INSULATION MATERIAL The insulation which must surround the conductive material must be capable of containing the current flow and provide a margin of safety in the event of a volt-surge. The most commonly used insulative material used in the low voltage range (1 -1000V) is P.V.C. or Polyvinylchloride. In the medium voltage range (1001 -36 OOOV) materials such as resin-impregnated paper and cross linked Polyethylene (XP.L.E.) are most commonly used. CABLE CONSTRUCTION Cables may be constructed in the following manner: a) Single Core -a single conductive core surrounded by a layer of bedding, usually P.V.C.. b) Bundled -several single core cables bundled (i.e. tied) together. Such an arrangement is mostly used on A.B.C. supply lines in low cost developments. c) Multi-core -two or more single cores are "encased" within a common "sheath" or "outer- serving". ARMOURING Any cable that is to be installed in such a way that it will receive a mechanical load upon it (e.g. buried underground) must be protected with a crush proof layer known as "armouring". The two basic types of armouring are: a) Steel wire armouring (S.WA) consisting of spiral wraps of galvanised steel wires surrounding the bedding layer around the conductor cores. b) Steep tape armouring (S.T.A.) consisting of two layers of light steel tape wound over a layer of bituminised bedding which usually surrounds a lead sheath. Steel tape armouring is not used with P.V.C. insulated cables. OUTER-SHEATHING The outer layer of cables is often called the "outer-serving". Depending upon the application, sitting and ambient conditions the outer-serving may be made from: a) P.V.C. b) Bituminised Hessian Tape (Jute) as in Paper/Lead Medium Voltage cables. c) Nitrile -a form of synthetic rubber. d) Silicon -also a form of synthetic rubber but with high abrasive resistant qualities.

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Many other compounds may be encountered which are designed to: o Reduce the risk of toxic fumes in the event of fire. o Reduce the effects of ultra-violet rays (sunlight). o Or even be used in submerged (underwater) situations. SCREENING Cables designed to operate from 15 kilovolts upward must have each core screened in order to direct electrical stresses to earth. Screening is normally effected by surrounding the cores with a layer of thin copper tape. ECC CABLES (EARTH CONCENTRIC CABLES) Many S.W.A. type cables have 3 or more of their wire-armouring strands made of copper. These strands are designed to provide an earth path to minimise shock hazard in the event of insulation failure within a consumer unit. CABLE RATINGS Cables are rated in terms of their insulation properties which is not to be confused with the normal working voltage. For example, a cable carrying a normal voltage of 220 volts (e.g. House Supply Cable) would be rated as 600 / 1000 volts. What this means is that the insulation is capable of withstanding 600 volts between any two adjacent conductor cores and 1000 volts between any conductor core and earth. The cable rating therefore is a built in safety feature for protection against volt surging.

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RESOURCE NOTES PART TWO: CABLE END PREPARATION

INTRODUCTION The majority of cable preparation work is most likely to be performed on S.WA type cable. For this reason we have decided to use this type in our visual demonstration. The procedure for un-armoured cables would in fact be similar except, of course, that you need not remove any armouring. Procedures for preparing other types (e.g. Paper/Lead and Medium Voltage X.P.L.E.) are visually demonstrated in the relevant DVD programmes. SOME GENERAL TIPS FOR CABLE END PREPARATION o Always use sharp cutting tools (e.g. knife and saw). Dull, or blunt tools will not only frustrate you but can be more dangerous as they are more likely to slip. o Use a wrap or two of P.V.C. insulation tape to mark the ring-cut positions. This not only guides you when you make a ring-cut but also results in a much more professional looking preparation. o When making a longitudinal cut, through the bedding layer, strive to keep your knife blade "between" conductors and thereafter follow the lay (i.e. the twist) as you cut through. o Practice your cutting until you can do it without nicking the conductor insulation. o Use a cutting board or rubber mat, wherever it is practically possible, to support the cable end during cutting operations. o Don't attempt to cut all the way through the armour wires. If you cut approximately half way through you will easily be able to break them off by bending them back and forth. This way you will not damage the bedding layer. o Remember, on ECC type armouring, to bend the copper wires back before you ring cut the others. (NB: To locate the copper wires you may need to lightly scrape off the galvanising layers until you see the copper colour). o When establishing the tail length required from the point of entry always measure to at least the furthermost termination point. Allow a little extra too, so that you don't find yourself short when you have to route the conductors to their terminations. CONCLUSION A neat looking cable end preparation is the mark of a good artisan. Sloppy workmanship can result in a dangerous condition. Be smart, do it well, do it right the first time!