BS7671:2008 +A3:2015 (Answers references to On-Site Guide) You may find it helpful to have a copy of BS7671:2008 +A3:2015 On-Site Guide.

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1 Eletrial supply systems: (Covering Outome 2 of Unit 304 Understand the priniples of internal and external earthing arrangements for eletrial installations for buildings, strutures and the environment (Level 3 NVQ Diploma in Installing Eletro-Tehnial Systems and Equipment / 91) BS7671:2008 +A3:2015 (Answers referenes to On-Site Guide) You may find it helpful to have a opy of BS7671:2008 +A3:2015 On-Site Guide. Question 1: TN-C-S, TN-S and TT are all types of? Earthing arrangement (2.1) Question 2: State the typial ross-setional-areas for: (a) The earthing ondutor and (b) the main protetive bonding ondutors installed in an installation having a single-phase supply and a 100A maximum servie ut-out fuse. (a) 16mm 2 and (b) 10mm 2 (Fig: 2.1(i), (ii) and (iii)) Question 3: The Distributor s ut-out, Energy meter and isolator swith (if provided), are the property of whih person/s? Distributors ut-out - property of the distributor (2.2.1) Energy meter - property of the meter owner or energy supplier (2.2.2) Isolator swith - property of the distributor (2.2.4) Question 4: A small portable generator with an output ranging from 0.2kVA to 10kVA singlephase is likely to have a floating earth, what does this mean? A floating earth means that there is no earth onnetion between the hassis of the portable generator and the earth onnetion on the soket-outlet of the unit. The earth soket-tube of the soket-outlet is onneted to the frame of the generator only. (See figure On-Site Guide). Question 5: Where a portable generator supplies eletrial equipment with exposed ondutive parts an earth eletrode should be installed. What is the funtion of the eletrode? To provide a referene for the generator to the general mass of earth; the eletrode does not form part of the earthing arrangement. (2.4.3 On-Site Guide)

2 Revision for AC iruit omponents: (Covering Unit 309 Outome 7 Understand how different eletrial properties an effet eletrial iruits, systems and equipment (Level 3 NVQ Diploma in Installing Eletro-Tehnial Systems and Equipment / 91 or EAL equivalent) Task 1: Complete the following to provide a revision summary. If two ondutive plates are arranged parallel to eah other and separated by a layer of insulation, and a voltage applied between the plates, an eletri harge will be reated. The desription above refers to whih type of eletrial omponent? A apaitor The eletri harge an be determined from the following formula. Complete the key. Q = I t Where Q = harge in Coulombs, I = urrent in Amperes and t = time in seonds The amount of harge that an be stored is determined by three fators, these are? (i) The area of the metalli plates (ii) The thikness of the insulation, (dieletri), between the plates (iii)the material used for the insulation, (dieletri). Complete the labels for the following diagram. Metalli plates Insulation Eletrial onnetion The illustration shows the basi onstrution of a: Capaitor The name given to the insulation is the: Dieletri

3 The apaitane, (symbol C) of a apaitor is measured in: Farads (symbol F) When a voltage is applied to a apaitor a urrent will flow. The urrent will redue in value as the apaitor reahes full harge. At full harge the urrent will be zero. If a harged apaitor is onneted into a iruit, the stored harge will be released. The disharge urrent will depend on the iruit properties generally however urrent will start high and then derease to zero as the apaitor fully disharges. If a apaitor is onneted to an alternating urrent (AC), iruit it will harge and disharge for as long as the supply is onneted. The opposition to urrent flow in a apaitor in an AC iruit is alled? Capaitive reatane (symbol X C ) measured in: (unit: Ohms symbol: Ω) The apaitive reatane of a apaitor onneted in an AC iruit depends on two fators, these are? (i) The Frequeny of the a.. supply (unit: Hertz, symbol: Hz) (ii) The Capaitane of the apaitor (unit: Farads, symbol: F) If a apaitor is rated in µf (miro-farads), state the formula to find apaitive reatane and make a key stating the name and unit symbol for eah relevant part of the formula: Formula: 1 X = 2 π f C Key: X = Capaitive reatane in Ω f = frequeny in Hz C = apaitane in Farads π = 3.142

4 Task 2: Pratie questions: 1) Calulate the apaitive reatane of a apaitor rated at 125µF when it is onneted into an a.. iruit operating at 50Hz. 1 X C = 2 x π x 50 x 125 x 10-6 = 25.5 Ω X C = 25.5Ω 2) A apaitor has 230V applied aross it and a urrent of 1.5A flows through it when onneted to a 50Hz a.. supply. Determine the value, (or rating), of the apaitor in µf. 1 X C = U o X C = 2 π f C I X C = C = 2 π f X X C = Ω 1 C = 2π x 50 x C = µf

5 Capaitors: (Covering Unit 309 Outome 7 Understand how different eletrial properties an effet eletrial iruits, systems and equipment (Level 3 NVQ Diploma in Installing Eletro-Tehnial Systems and Equipment / 91 or EAL equivalent) Question 1: Complete the following statement: A apaitor onsists of at least two metalli plates (A), separated by an insulator alled a dieletri (B). When a voltage is applied to the plates an eletri harge an be stored. Question 2: By using the letter odes in question 1, omplete the labels on the diagram: B A A Question 3: Identify the orret names for eah of the apaitor symbols shown below. Symbols: + General Eletrolyti Variable Pre-set adjustment Or Polarised

6 The following table illustrates some types of dieletri used in apaitor manufature, the maximum eletrial stress voltage (MV) the insulator an withstand and typial appliations of the apaitors. Material Max. Eletrial Stress Voltage (MV) Appliation Air 2 Variable apaitors. Mia 100 High frequeny apaitors Paper 5 General purpose apaitors Polythene 40 Higher quality than paper general purpose uses Insulating Oil 50 Industrial apaitors used for power fator orretion. Capaitor Fats: Question 4: Complete the missing words in the following statements. Unit of apaitane: The Unit of Capaitane is the farad, symbol F The farad shows how muh eletri harge an be stored in a apaitor per volt applied aross the apaitor terminals.

7 Quantity of stored harge: The quantity of eletriity stored an be expressed as: Q = CV Q = harge measured in oulombs C = apaitane of the apaitor in farads V = the p.d. aross the plates measured in volts Dimensions: The apaitane of a apaitor relies on the physial dimensions of the apaitor: a) Capaitane is diretly proportional to the physial area of the plates and b) Capaitane is inversely proportional to the distane between the plates, i.e. the thikness of the dieletri. Eletri field: When a apaitor is harged, an eletri field will exist between the plates. The eletri field an be inreased by inreasing the applied voltage. If the applied voltage exeeds the dieletri stress voltage limit, (alled the eletri field strength ), the dieletri will break-down resulting in a short - iruit between the plates; the apaitor will be destroyed and annot be repaired. Eletri field strength an be found by the potential differene (p.d), aross the plates (V), being divided by the distane, (d) between the plates: E = V E is expressed in volts per metre. d

8 Energy stored in a apaitor: The energy stored in a apaitor depends on its apaitane and the square of the potential differene, (p.d), aross it. Energy (W) = ½ CV² measured in Joules. Question 5: Find the energy stored in a 100µF apaitor that has a p.d. of 200V aross it. Energy (W) = ½ CV² W = 0.5 x 100 x 10-6 x Use 10-6 beause apaitor is in µf Connetion arrangements: Capaitors an be onneted in series, parallel or a ombination of series and parallel. Question 6: Complete the following summary for the total apaitane of a apaitor. i. Capaitane will be inreased with a greater area of the plates ii. Capaitane will be dereased if the thikness of the dieletri is inreased Question 7: Complete the following statements for ombinations of apaitors. i. Capaitane will be inreased if apaitors are onneted in parallel with eah other. ii. Capaitane will be dereased if apaitors are onneted in series with eah other.

9 Question 8: Identify two formulae that an be used to determine the total apaitane of a group of apaitors onneted in (a) series, and (b) parallel. (a) 1 = et note: total apaitane dereases C T C 1 C 2 C 3 omplete opposite to resistane (b) C T = C 1 + C 2 + C 3 et note: total apaitane inreases - omplete opposite to resistane

10 Question 9: Two apaitors 12µF and 8µF are onneted in series aross a 10V d supply. Calulate the total apaitane of this iruit. 1 = C T C 1 C 2 1 = = C T = C T So C T = 1 = 4.8µF Note: In this example there is no need to hange µf to farads. Or C T = C 1 C 2 C 1 + C 2 = (12)(8) = = 4 1 8µF Note: This method only works with 2. Question 10: Determine the eletri harge on eah of the two apaitors in question 1 above. Q = C V Q = 4.8 x 10 Q = 48µC

11 Warning: All apaitors have the ability to retain stored harge; it is therefore dangerous to touh the terminals of a apaitor without first ensuring that it is disharged. Disharging an be arried out in a number of ways: a) By the use of a high ohm disharge resistor permanently onneted aross the apaitor terminals. b) By shorting - out the terminals using a substantial piee of well insulated wire (not preferred.) NOTE: It is imperative that safety glasses be worn whilst disharging a apaitor as hot metalli partiles ould be repelled from the ar should the devie be fully harged.

12 Revision for AC iruit omponents: (Covering Unit 309 Outome 7 Understand how different eletrial properties an effet eletrial iruits, systems and equipment (Level 3 NVQ Diploma in Installing Eletro-Tehnial Systems and Equipment / 91 or EAL equivalent) Task 1: Complete the following to provide a revision summary. When a oil of wire, suh as a motor winding, transformer winding, indutor or hoke (ballast), is onneted to an alternating urrent supply, opposition to urrent flow is aused by two onditions, these are? i) Resistane and (ii) Indutane The ombined effet of these two onditions is alled? Indutive reatane (symbol X L ) measured in: (unit: Ohms symbol: Ω) The indutive reatane of a oil depends on two fators, these are? (i) The Frequeny of the a.. supply (unit: Hertz, symbol: Hz) (ii) The Indutane of the oil (unit: henry, symbol: H) Label the following diagram using orret terms at (i), (ii) and (iii) (i) Current (iii) Indutive reatane (ii) Voltage State the formula for indutive reatane and make a key stating the name and unit symbol for eah relevant part of the formula: Formula: Key: X L = 2 π f L X L = Indutive reatane in Ω f = frequeny in Hz L = indutane in henrys π = 3.142

13 Task 2: Pratie questions: 1) Calulate the indutive reatane of a oil of 0.26H when it is onneted into an a.. iruit operating at 50Hz. X L = 2 π f L X L = 2 x π x f x L X L = 2 x π x 50 x 0.26 X L = Ω 2) A oil has 200V measured aross it and a urrent of 1.85A flowing through it when onneted to a 50Hz a.. supply. Determine the value, (or rating), of the indutor, in henrys. X L = U o I X L = X L = Ω X L = 2 π f L L = X L 2 π f L = x π x 50 L = H 3) Determine the urrent flowing through a oil of 0.65H when onneted to a 230V 60Hz a.. supply. X L = 2 π f L X L = 2 x π x 60 x 0.65 X L = 245 Ω I = U o X L I = I = 0.94 A 4) Calulate the voltage aross an indutor of 0.25H when the urrent flowing through it is 2.65A at 48Hz. X L = 2 π f L U o = I x X L X L = 2 x x 48 x 0.25 U = 2.65 x 75.4 X L = 75.4 Ω U = V (200)

14 Initial verifiation of eletrial installations: Answers (Covering Unit 307 Understand priniples, praties and legislation for the inspetion, testing ommissioning and ertifiation of eletro-tehnial systems and equipment in buildings, strutures and the environment (Level 3 NVQ Diploma in Installing Eletro- Tehnial Systems and Equipment / 91 and the EAL equivalent) Task 1: omplete the following questions regarding the priniples, praties and legislation for the initial verifiation of eletrial installations. Referene (GN) is for the IET Guidane Note 3 doument 1) State two oasions when initial verifiation an be arried out. Answer: during onstrution and on ompletion of the installation (page15 GN3) 2) Identify two aspets of BS7671 that initial verifiation will onfirm. Answer: design and onstrution (page15 GN3) 3) When an inspetor arries out an initial verifiation explain why inspetion and testing an only be so far as is reasonably pratiable? Answer: It would not be possible for an inspetor to onfirm the orret size able has been installed throughout its length due to the able being buried or enlosed within the fabri of the building. However he/she may onfirm the orret able size at a distribution board. (page15 GN3)

15 4) Identify the three BS7671 generi requirements for items to be verified during the initial verifiation proedure. Answer: Equipment is orret type and omplies with appliable British Standards, or equivalent The fixed installation is orretly seleted and ereted The fixed installation is not visibly damaged (page15 GN3) 5) State the orret title of the statutory doument that onerns inspetion and test reords, and identify the length of time reords must be kept. Answer: The Eletriity at Work Regulations 1989, and in partiular Regulation 4(2). The Memorandum of guidane on the Eletriity at Work Regulations (HSR25) reommends reords be kept for the lifetime of the installation. (page16 GN3) 6) Briefly explain the meaning of the term Relevant riteria in respet to the initial verifiation proess. Answer: The designer may have made speifi requirements for a given installation; as suh the inspetor will need to ask for these requirements or, if relevant, forward a opy of the test results to the designer for verifiation. (page16 GN3) 7) State who is responsible for omparing and verifying inspetion and test results with relevant riteria for an installation. Answer: The person responsible for inspeting and testing the installation. (page16 GN3)

16 8) State the orret titles of three ertifiates that apply to a new installation or additions to an existing installation. Answer: Eletrial Installation Certifiate multiple-signature Eletrial Installation Certifiate single-signature Minor Eletrial Installation Works Certifiate (page16 GN3) 9) List three items of required information regarding the assessment of general harateristis for an installation. Answer: Maximum demand Number and type of live ondutors Type of earthing Nominal voltage Supply frequeny Prospetive short-iruit urrent Earth fault loop impedane (Ze) Type and rating of overurrent protetive devies See page 17 of GN3 10) The Health and Safety at Work At 1974 requires relevant information to be available for what purpose? Answer: safe use / inspetion & testing / maintenane (page17 GN3)

17 Eletrial Instrument readings: Answers In the following exerise math eah unit with its measured unit No. Unit Measured Unit 1 Current 2 x 10 3 A 36mA 2 Voltage 132 x 10 3 B 45000Ω 3 Resistane 150 x 10 6 C 6kW 4 Current 36 x 10-3 D 150MΩ 5 Resistane 45 x 10 3 E 20MW

18 6 Power 60 x 10 2 F 132kV 7 Power 20 x 10 6 G 2kA 8 Voltage 400 x 10 6 H 400MV Solutions: 1 G 5 B 2 F 6 C 3 D 7 E 4 A 8 H

19 Cable Seletion: Revision multiple-hoie questions (Covering Outome 6 of Unit 305, Understand the praties and proedures for installing wiring systems, assoiated equipment and enlosures, (Level 3 NVQ Diploma in Installing Eletro-Tehnial Systems and Equipment / 91 or EAL equivalent) 1 The term Ib is used to identify whih one of the following? a b Current rating of the iruit protetive devie Rating fator for ambient temperature Current rating of the able d Design urrent of the iruit X 2 If a BS3036 semi-enlosed fuse is to be used to protet a able the orret symbol and rating fator is? a Cf X b Cr Cf d Cr Identify the orret symbol and rating fator for a able installed in ontat with thermal insulation for 400mm of its length a Ci 0.88

20 b Cf 0.78 Cs 0.63 d Ci 0.51 X 4 The reommended maximum voltage drop allowane for a lighting iruit is: a 1% b 2% 3% X d 5% 5 An extra-low nominal voltage is? a 25V X b d 200V 230V 250V 6 In able seletion, when applying a rating fator for groups whih of the following statements is orret?

21 a b Fators apply to the number of ores in the able Fators apply to the number of iruits existing Fators apply to the number of iruits in total X d Fators apply to the ores in a multi-ore able 7 The urrent rating of a single-ore 16mm², 70ºC thermoplasti insulated, non-armoured able, lipped diret to a surfae and supplying a three-phase load is? a 87A b 79A X d 68A 61A 8 The mv/a/m rating for a 10mm² multi-ore armoured 70ºC thermoplasti insulated able supplying a single phase load is? a 4.4 X b d The urrent and mv/a/m rating for a 2.5mm² 70ºC thermoplasti insulated able installed to Method 101 is?

22 a b 27A and 18mV/A/m 21A and 18mV/A/m 17A and 18mV/A/m X d 13A and 29mV/A/m 10 The referene method to be used to determine urrentarrying apaity of non-sheathed ables enlosed in onduit on a masonry wall, is? a Referene Method A b Referene Method B X d Referene Method C Referene Method D

23 Periodi Inspetion and Testing of eletrial installations: (Covering Unit 307 Understand priniples, praties and legislation for the inspetion, testing ommissioning and ertifiation of eletro-tehnial systems and equipment in buildings, strutures and the environment (Level 3 NVQ Diploma in Installing Eletro- Tehnial Systems and Equipment / 91 and the EAL equivalent) Pratie Multiple-hoie questions: 1 Whih one of the following is onerned prinipally with Part 6 of BS7671? a Eletriity at Work Regulations 1989 b Building Regulations Eletriity, Safety, Quality and Continuity Regulations d IET Guidane Note 3 X 2 To enable an eletrially skilled person to onstrut an installation and to ommission it, whih doument is required? a IET BS7671:2008 b Eletriity at Work Regulations 1989 The Speifiation X d Part P of the Building Regulations 3 Preise details regarding eletrial equipment to be installed must be obtained from? a The equipment manufaturer X b The lient Main ontrator d Eletriity supplier 4 Eletrial test instruments should onform to whih of the following British Standards? a HS (G) 141 b HSE Guidane EAWR 1989 d BS EN X

24 5 Eletrial shok hazards may arise from parts of an eletrial installation, espeially? a Resistive loads b Eletri heating systems Voltages on earthed metalwork d Capaitive loads X 2 6 The responsibilities of an inspetor are eah of the following exept? a No danger ours to persons, livestok and property during testing b Comparing the test results with design riteria Consider the ondition of the installation and advise aordingly d Issue prohibition noties X 7 The requirement for inspeting and testing the eletrial installation for a house of multiple oupany, is that it must be inspeted and tested at least? a Annually b Every two years Every five years X d Every ten years 8 When inspeting an installation for the first time the purpose is to verify eah of the following exept? a No part of the installation is damaged b Test results omply with previously obtained data X Parts of the fixed installation are orretly seleted and ereted d Installed eletrial equipment is of the orret type 9 Reords onerning the ondition of the eletrial installation of domesti or non-domesti premises may be required by eah of the following exept? a The person arrying out the inspetion and testing

25 b The owner of the premises The oupant of the premises d The main building ontrator X 10 A re-inspetion & next test date for an existing installation is deided by? a The lient b Eletrial designer Eletrial ontrator d The person arrying out the inspetion and testing X 11 Completion of the eletrial design, onstrution and inspetion when arried out by different persons requires the issue of? a A Minor Works Certifiate b Eletrial Installation Certifiate X Shedule of test results d NICEIC membership 3 12 Inspetion an be undertaken? a Throughout different stages of onstrution X b On ompletion of the installation On ompletion of the onstrution d If required during ommissioning of the installation 13 The first three tests to be arried out on a typial domesti 32A soket iruit is likely to be? a Continuity of protetive ondutor / ontinuity of ring final ondutors / insulation resistane b Continuity of protetive ondutor / polarity / insulation resistane Continuity of protetive ondutor / insulation resistane / polarity X

26 d Insulation resistane / polarity / ontinuity of protetive ondutors 14 A Thermographi survey on eletrial equipment is usually arried out on? a b d Swith-gear in domesti premises before ompletion Swith-gear in ommerial and industrial premises during use Any swith-gear during mehanial maintenane proedures Eletrial able routes in all premises X 15 A radial iruit 50m in length is wired with a able having 4.61mΩ/m, (mω per metre), at 20 C the expeted able resistane when arrying out a Method 2 ontinuity test is likely to be? a 2305Ω b 2.305Ω 0.460Ω d Ω X

27 Eletrial Mahines: (Covering Outome 8 Understand the operating priniples and appliations of DC mahines and AC motors of Unit 309 NVQ Level 3 Diploma and EAL equivalent) Power Transfer Power Transfer onerns the proess of onverting eletrial energy into mehanial energy. Question 1: Give ONE example of a devie that demonstrates eletrial to mehanial power transfer. Answer: The eletri motor Power transfer an also work in the opposite diretion, i.e. a onversion from mehanial energy to eletrial energy. Question 2: Give ONE example that onverts mehanial to eletrial energy. Answer: The eletrial generator Losses: In the proess of transferring energy some losses will our.

28 Question 3: Identify ONE example that will ontribute to a mehanial loss in a mahine and ONE example of how this loss is minimised in pratie. Answer: Frition between fixed and rotating parts Frition an be minimised with the use of good quality bearings and lubriation In eletrial mahines, apart from mehanial losses there are other losses. Question 4: State TWO losses, other than mehanial losses, that an our in an eletri motor. Answer: Copper losses - known as the I 2 R loss due to urrent in the opper windings Iron losses these are due to Eddy Currents induted in the metal frame of the mahine, and Hysteresis loss aused by ontinually reversing magneti fields within the mahine struture Effiieny: (Symbol η Greek letter Eta ) The effiieny of an eletri motor is the ratio of mehanial power output to the eletrial power input. Question 5: Complete the labels on the diagram below Eletrial power input M Mehanial power output Losses

29 Formula: To alulate the effiieny of a mahine suh as an eletri motor one of two formulae an be applied: i. Effiieny η = Output power x 100 (Expressed as a perentage) (%) Input power or ii. Effiieny η = Output power (Expressed as a per-unit value) (p.u) Input power Example: Calulate the effiieny as a per unit value, and as a perentage, for a 230V single-phase eletri motor drawing 15A with a full power output of 2880W. Solution: Advie: It is always advisable to show the arrangement in a simple drawing first. Input power to be determined Output power: 2880W Losses: unknown Input power an be found from basi priniples, i.e. P = U x I P = 230 x 15 = 3450Watts Effiieny η = Output power so Effiieny η = 2880 therefore η (per unit) = 0.84 Input power 3450 Expressed as a (%) Effiieny η = 0.84 x 100 = 84% (So there are 16% losses) Question 6:

30 Calulate the urrent taken by a 2kW, 230V eletri motor operating at full load with a power fator of 0.6 and an effiieny of 70% Input power and urrent to be determined Output power: 2kW Losses: 30% Advie: First step: alulate the input power to the motor by rearranging the formula: Effiieny η = Output power x 100 Input power So Input power = Output power x 100 η Input power = 2000 x = 2857W or 2.857kW Seond step: alulate input urrent from rearranging the formula: Power fator pf = Watts (W) Volts x Amps Note1: the Watts in the formula will be the input power of the motor. Current (A) = W V x pf = 2857 = 20.7A 230 x 0.6 Note 2: Both mehanial power output and eletrial power input share the same Unit, i.e. Watts. This makes power transfer alulations straightforward.

31 Priniples and praties for testing eletro-tehnial systems: (Covering Unit 307 Understand priniples, praties and legislation for the inspetion, testing ommissioning and ertifiation of eletro-tehnial systems and equipment in buildings, strutures and the environment (Level 3 NVQ Diploma in Installing Eletro- Tehnial Systems and Equipment / 91 and the EAL equivalent) Test instruments: Complete the following questions regarding eletrial test instruments and test sequene: 1) List the eletrial test instruments whih give the following units. a) MΩ b) ka ) ms a) Insulation resistane ohmmeter b) Prospetive short iruit urrent tester ) RCD tester 2) State THREE safety heks to be arried out on an earth fault loop impedane tester and leads before use. Test probes should have finger guards Test probe metal tips should not exeed 4mm but preferably 2mm Test leads should be fused 3) State the iruit lassifiation for eah of the following insulation test instrument voltages: a) 250 V d b) 500 V d ) 1000 V d a) SELV iruit and PELV b) Low voltage iruit (up to and inluding 500V exeption to SELV and PELV) ) Low voltage iruit (above 500V) 4) A reading of 10Ω is obtained when arrying out a resistane measurement on a 10mm 2, 150m long main protetive bonding ondutor on a mains water supply servie: i. Suggest one possible reason for this reading ii. Suggest a solution based on the reason given in (i)

32 iii. Calulate the expeted reading based on the information given and the resistane per metre of opper able being 1.83µΩ / m (miro ohms per metre) i. Reading ould be due to a loose termination. Alternative answers ould be a poorly fitted bonding lamp. Clamp fitted to a dirty or orroded pipe. Instrument not alibrated orretly. Test leads damaged or badly onneted. ii. Loose terminal should be identified and tightened. Alternative answers:- re-fit bonding lamp after leaning pipe and lamp. Chek test instrument batteries have good harge and alibration is orret. Carefully hek ondition of test leads and any damage will require new leads to be fitted. iii. R = Cable resistane per m x length of able R = 1.83 x 150 R = µω or Ω Note: in pratie low reading resistane test instruments do not indiate measurements this small. 5) List in the orret sequene, the first THREE tests that should be performed during an initial verifiation on a new lighting installation. Continuity of protetive ondutors inluding main and supplementary bonding Insulation resistane polarity 6) The test for the ontinuity of a p in a radial iruit feeding one soket-outlet uses a temporary link and a low reading ohmmeter. State: a) where the temporary link is onneted b) where the low reading ohmmeter is onneted ) what the meter reading atually represents a) between line and iruit protetive (earth) ondutor at the onsumers ontrol unit (good pratie to disonnet both) b) between line and earth at the soket outlet ) the value measured is (R1 + R2) for the iruit 7) List THREE preautions to be taken before onduting an insulation resistane test on power iruits loated in a large ommerial installation.

33 i) Obtain all relevant information regarding the iruit/s to be tested ii) Obtain permission to isolate the iruit from the supply iii) Obtain permission to disonnet eletrial equipment that may be damaged by test voltages when iruits are tested 8) A periodi inspetion and test is to be arried out on a ommerial offie lighting installation. Identify the preautions to be taken regarding this type of inspetion and test. i) Establish if there are standby power supplies that an be ativated when the mains supply to the lighting iruits is isolated. ii) Identify the type of luminaire it may have eletroni ontrol gear that an be damaged by high test voltages iii) Chek whether luminaires have power - fator orretion apaitors installed as they may remain harged when the supply is isolated. 9) State the main reason for onduting a periodi inspetion and testing on an eletrial installation. BS7671: A3 2015; Regulation Periodi inspetion and testing of every eletrial installation shall be arried out in order to determine, so far as is reasonably pratiable, whether the installation is in a satisfatory ondition for ontinued servie

34 Eletro-Tehnial Siene Revision Quiz: (Covering Unit 309 (Level 3 NVQ Diploma in Installing Eletro-Tehnial Systems and Equipment / 91 or EAL equivalent) True or False: For eah question deide if the answer or statement is true or false. You may need to refer to your notes, text books or, where neessary, omplete a alulation to see if the answer is orret or not. 1) Eletri urrent flows when a potential - differene is onneted aross a ompleted iruit? TRUE ü FALSE 2) Conventional eletri urrent flows from the negative to the positive terminal in a iruit supplied by a battery? Conventional urrent flows from positive to negative and Eletron urrent flows from negative to positive Conventional urrent so alled beause it was assumed that this was the diretion urrent flowed round a iruit until atomi theory was understood. TRUE FALSE ü

35 3) The unit measurement for potential-differene is Amperes? The unit of potential-differene (pd) is the Volt. The Ampere is the measurement of urrent flow TRUE FALSE ü 4) Energy is measured in Joules and represents the ability to do work? TRUE ü FALSE 5) The rate of doing work is measured in Watts and an be found from the formula:- P = V x I or P = U x I TRUE ü FALSE

36 6) The resistane of a ondutor dereases with inreasing length and inreases with dereasing ross-setional-area? The resistane of a ondutor inreases with inreased length and does inrease with dereasing ross-setional-area, so half the statement is true, but overall the statement is false. TRUE FALSE ü 7) The symbol represents a semi-ondutor diode? TRUE ü FALSE 8) The right-hand grip rule is used when trying to determine the diretion of urrent flow in a oil? There are a number of right-hand rules: The right-hand grip rule onerns straight ondutors; the thumb of the right-hand points in the diretion urrent is flowing in the ondutor and the fingers indiate the diretion the magneti field is revolving about the ondutor. The right-hand grasp rule applies to a oil of wire, where the thumb points to the end of the oil that is North when the fingers point in the diretion the oils are wound. TRUE FALSE ü

37 9) The fore exerted on a urrent- arrying ondutor when it is lying at right-angles in a magneti field an be found by applying Flemings RIGHT-HAND rule? The ondutor is arrying urrent and so will produe a magneti field around itself. This field will be opposed by the magneti-field the ondutor is lying in and the ondutor will be rejeted; this is the motor priniple represented by the left-hand rule. The right-hand rule applies to the generator priniple TRUE FALSE ü 10) The inandesent lamp works on the priniple of an eletri urrent flowing through a filament? TRUE ü Now hek your answers. FALSE

38 WORDSEARCH Speial loations Try to find the following words that are all Speial Loations. (Answers an be left to right, right to left, up or down) Bath Medial Booth Shower Solar Fairground Sauna Mobile Vehile Demolition Transportable Maintenane Agriultural Exhibitions Marina Restrited Caravan Gangway A B C O N T A C N O I T A T O R F M T H S N O I T I B I H X E M I W S E I O U P E E S T E I D T E D L A C I D E M A L L S K E L E C T R O D E C A L O L E X K F U E A M A I N T C O N O R E W C F H U K C E R T G F I C A T O F A A E I A I E U H A T M R E R C N P I A V E R H T A B N O M O B I L E T O Y T U A F O E R I O T C O I L C E W L A B I G N A R V A T O A K A N C U C O A S O L A R E B O N P T Y G L G T L A H U K L O N U V L O S O H N N E A R T N S S A L M G I O N G P C N J I C U R U A T I N O E W A R G C O A S N A F A I R G R O U N D A T P L T R Y W J N E T U A H E A A P R Y I W O L T H I I I Y P R L T E S S I V E A R K E A W T O R E S T R I C T E D T R P A F A B L T Q A E O H N I U D A R P L F A M A L T H N M A I N T E N A N C E C S I D I E G Y X P S F T E S V E Q S E B V J U Y K L E S

39 End of Year Revision: Eletrial Siene & Priniples (Covering Unit 309: Understanding the eletrial priniples assoiated with the design, building, installation, and maintenane of eletrial equipment and systems (Level 3 NVQ Diploma in Installing Eletro-Tehnial Systems and Equipment / 91 or EAL equivalent) Attempt the following Multiple Choie questions 1 Three resistors of 10Ω, 25Ω and 53Ω are onneted in parallel with eah other. The total resistane will be? a b Higher than 53Ω Higher than 25Ω Total of 88Ω d Lower than 10Ω X 2 Three resistors are onneted to a parallel iruit. Two of the resistors are rated at 107Ω alongside a 35Ω resistor. Calulate the total resistane of the iruit. a 3.05Ω b 13.5Ω 21.16Ω X d 142Ω

40 3 The total resistane of a series iruit is 150Ω. If the iruit onsists of five resistors, and one resistor is 10Ω, what is the value of the remaining four? a 140Ω X b d 112Ω 100Ω 9Ω 4 When urrent passes through a ondutor in one diretion a b Heat is generated An alternating magneti field is produed in the ondutor Eletrons flow from positive to negative d A magneti field is set up around the ondutor X

41 5 When urrent in a ondutor is shown by the symbol the urrent is a Alternating b Flowing away from the viewer X d Flowing towards the viewer Positive 6 If urrent is flowing as shown in the symbol of question 5 above, the magneti field produed will be? a Moving lokwise around the ondutor X b d Moving anti-lokwise around the ondutor Passing over the length of ondutor Alternating aross the ondutor 7 Magneti flux density is measured in? a b Webers Joules Farads d Teslas X

42 8 Fore ating on a urrent arrying ondutor lying at 90 to a magneti field is measured in? a Joules b Newtons X d Watts Webers 9 A ondutor 100m long and arrying 5A is lying at 90º to magneti field of 1.5T, what is the fore on the ondutor? a 750N X b 115N 107.5N d 100N 10 Calulate the indued voltage in a 500m long ondutor when it is passing through a flux density of 3T at a rate of 3m/s a 500V b 4.5kV X 450V d 55.5V 11 What is the resistane of 1000m of 1.5mm² opper able is if the ondutor resistivity is given as 17.2μΩ/m?

43 a b 0.85 Ω 0.95 Ω Ω d Ω X 12 The proton has what type of eletrial harge? a Negative b Positive X d None Equal positive and negative 13 What is the assumed urrent demand for an eletri heating element rated at 12kW when onneted to a 230V supply? a 0.52A b 2.42A 5.22A d 52.2A X

44 14 If a distribution iruit able is supplied at end A with 230v, and resistive loads are taken from it at points B and C, if the overall voltage drop from A to C is 2.6%, the voltage at C will be? a 220V b V X d 226V 598V 15 If an eletri motor has a rated output of 20kW and an effiieny of 78%, the eletrial input to the motor will be? a b 15.60kW 21.00kW 24.00kW d 25.64kW X 16 An auto-transformer operates on the priniple of? a Self-indution X b Mutual indution

45 d Impedane resistane 17 A transformer has a rating of 6000VA, if the output voltage is 110V what is the total urrent that an be delivered? a 0.2A b 32A 50A d 54.6A X 18 A step down transformer has a primary voltage of 230V and a seondary voltage of 50V The turns ratio for this transformer is a 9.6 : 1 b 6.9 : : 1 X d 4.2 : 1 19 The line voltage of a star onneted transformer is 440V. What is the phase voltage?

46 a 230V b 254V X d 400V 420V 20 If the measuring range of a voltmeter is to be extended whih one of the following is used? a Multiplier X b d Shunt resistor Diode Diode shunt

47 Pratie multiple-hoie questions: (Covering Unit 309 Outome 8, Understand the operating priniples of d and a motors (Level 3 NVQ Diploma in Installing Eletro-Tehnial Systems and Equipment / 91 or EAL equivalent) No 1 In a 3-phase eletri motor, speed is determined by knowing the frequeny of the supply and? Answer a b Voltage Current Power rating d Number of pairs of poles X No 2 The speed of a 3-phase eletri motor is 1000 r.p.m, this refers to the? Answer a Speed of the stator b Speed of the rotor X d Synhronous speed Point where the motor reahes full power No 3 The differene between synhronous and asynhronous speed of an indution motor is usually expressed as? Answer a b Wasted energy A power loss A per-unit value

48 d A perentage X No 4 A 3-phase indution motor has a synhronous speed of 750 rpm and a shaft speed of 715 rpm, what is the slip? Answer a 95.3% b 9.53% 4.67% X d 2.45% No 5 A six pole AC indution motor is onneted to a threephase supply of 50Hz. The synhronous speed of the stator flux is Answer a 750rpm b 1000rpm X d 1500rpm 3000rpm No 6 The starting urrent of an eletri motor is higher than the running urrent beause there is? Answer a No bak-emf on start-up X b A high load to move

49 d Full power on start-up Usually a starting devie used No 7 Single - phase indution motors are likely to be fitted with whih one of the following devies? Answer a b Voltage relay Star-delta starter Indution relay d Centrifugal swith X No 8 A 3kW single-phase eletri motor will generally be fitted with? Answer a Start and run windings X b d Starting resistane Variable resistane Run windings No 9 Whih of the following statements is true for singlephase apaitor start, indution run eletri motors? Answer a b The apaitor remains in iruit all the time the motor runs The start winding and apaitor are onneted in parallel

50 d The run winding and the apaitor are onneted in series The start winding and apaitor are onneted in series X No 10 The omponent shown in the figure below is usually found in whih type of AC motor? Answer a b Cage indution Dual age indution Universal X d Synhronous