Exam Paper 1 - 2391

Exam Paper 1
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   Examination Questions These 5 pages are copies of actual City & Guilds 2391 Examination Questions. These questions can be used asan invaluable aid to your learning Examination Inspection, Testing and Certification of  1830-21 00  21/2 hours Electrical Installations Paper  Inspection, testing and certification You should have the following for this examination: one answer book and non-programmable calculator This examination consists of two sections. Section A  - Twenty short answer questions worth three marks each Candidates must answer ALLTWENTY questions. It is recommended that candidates allow approximately one hour for this .section. Section B  - Six structured questions worth 15 marks each. Candidates must answer ALL SIX questions It is recommendedthat candidates allow approximately 11/2 hours for this section. Section A - Answer ALL TWENTY questions. All questions carry equal marks. 1 State the a) legal document that requires a person to be 'competent' in order to work on an electrical system(1 mark) b) title given, in law, to such a person(1 mark) c)British Standard number of a non-statutory document that may be used in evidence in a court of law to claim compliance with a statutory document.(1 mark)2 Give ONE possible reason for the issue of each of the following a) an electrical installation certificate(1 mark) h) a periodic test report (1 mark) c) a minor works certificate(1 mark)3 State the type of protection against electric shock offered by a) barriers and enclosures (1 mark) b) placing out of reach (1 mark) c) an RCD with l n 30 mA or less (1 mark)4 For which THREE stages in a small installation may one person authenticate an Electrical Installation Certificate' (3 marks)5 Identify the label/nonce which should be placed on an a) earth clamp connection (1 mark) b) enclosure, housing equipment where the voltage may be higher than 230V (1 mark) c) RCD regarding the frequency ol operation of its integral test facility. (1 mark)See next page 6 State a) the TWO documents that must be accompanied by both inspection schedules (2 Marks) and schedules of test results b) the person who is responsible for recommending the period of time between periodic tests. (1 Mark)7 State THREE requirements of GS38 regarding instrument test leads. (3 Marks)8 State the units of measurement that are displayed on the following test instruments a) low resistance ohmmeter (1 Mark) b) insulation resistance tester (1 Mark) c) prospective fault current tester. (1 Mark)9 State the points in an installation between which the following are connected a) an earthing conductor (1 Mark) b) a distribution circuit (1 Mark) c) a final circuit. (1 Mark)10 State the effect on thea) insulation resistance of a cable if its length is increased (1 Mark) b) temperature of a conductor if the current it carries is reduced (1 Mark)c) resistance of a conductor if the ambient temperature is increased. (1 Mark)11 When inspecting and testing main equipotential bonding conductors during an initial verification, state a) where they should be connected on Gas and Water services (1 Mark) b) the instrument to be used for checking continuity (1 Mark) c) the action to be taken regarding the test leads. (1 Mark)12 State the earthing system that relies on an earth return path of  a) the general mass of earth (1 Mark) b) a combined earth/neutral of the supply cable (1 Mark) c) a separate metallic conductor (1 Mark)13 A continuity test between  P and N  is conducted on a final ring circuit comprising 2.5 mm 2 /1.5 mm 2  thermoplastic (pvc/pvc) cable Readings at two socket outlets close to each other indicate an increased value to that of all the other sockets. State a) the instrument used for the test (1 Mark) b) TWO possible reasons for the increased readings. (2 Marks)14 As part of a periodic test an insulation resistance test is to be conducted on a 230 V circuit containing several explosion resistant luminaries State the a) instrument to be used(1 mark) b) voltage to be applied(1 mark) c) reason why the switch controlling the luminaires may be left in the off position(1 mark)15 State a BS 7671 special location which would a) require the use of a reduced low voltage system (1 mark) b) prohibit the use of a socket outlet other than a SELV socket (1 mark) c) use a 500 mA RCD for protection against fire. (1 mark)16 State a) the instrument to be used for a ‘dead’ polarity test (1 mark) b) an instrument that may be used for a ‘live’ polarity test (1 mark) c) why certain EI4 & E27 Edison screw lampholders do not require to be checked for polarity (1 mark)17 State a) why maximum values of earth fault loop impedance given for fuses protecting circuits on construction sites arc lower than those for ordinary installations  ( 1 mark) b) TWO reasons for correcting measured values of earth fault loop impedance so that a comparison with maximum values can be made,(2 marks) 18 The maximum tabulated values of earth fault loop impedance for three circuits are 7.74 ohms, 3.04 ohms & 1.41 ohms. If the measured values for these circuits are 6.8 ohms, 2.1 ohms & 1.2 ohms, determine (showing all calculations) if the measured values arc acceptable.(3 Marks)19 A test result sheet indicates that the total earth loop impedance value (Zs) of a circuit is lower than the sum of Ze+(RI+R2). State THREE possible reasons for this.(3 Marks)20 For an RCD, state a) how often its integral lest facility should be operated(1 Mark) b) the purpose- of the manual test(1 Mark) c) the maximum opening time of a 100 mA device.(1 Mark) SECTION BAll questions refer to the following scenario and Fig. 1 (attached). A farmer has built a horse riding complex comprising 12 individual stables, a tack room and a store room.The construction is blockwork on a concrete oversite with a traditional timber and tile pitched roof. Thesupply to the complex is via a 3 core thermoplastic (pvc) SWA cable distribution circuit from the mainfarm house (3rd core is used as a cpc)The distribution circuit board is located in the store room.The earthing system is T N-S and the voltage at the house intake is 230V 50 Hz with a measured value of  Ze of 0.2 ohm and a PFC. of 1.4kA The electrical system for this new block comprises enclosed fluorescent luminaires in the apex of eachsection with switching outside each stable and inside for the tack and store room.Radial socket outlet circuits art- provided in the tack and store rooms and outside the complex for general use for cleaning/jet hosing etcI'hree Tungsten Halogen luminaries, with integral PIR detectors (time clock controlled with over-ride),are provided outside the complex1'hc whole system is surface pvc conduit/trunking with thermoplastic (pvc) single core cables(cpc's same size as phase conductors)The water supply to the complex is via a plastic pipe from the main house. An inspection and test of this complex is to be undertaken21 State a) the overall type of verification to be conducted(1 Mark) b) the certificate to be completed(1 Mark) c) the documents that must accompany the certificate in b)(2 Marks) d) who should retain the original copy of the documents in b) and c)(1 Mark) e) the type of venfic .tuon thai would be needed for the additional load at the house(1 Mark) f) which FOUR items in particular would need inspecting in e)(4 Marks) g) the certificate and documents that would need completing for e)(3 Marks) h) who should decide when the next inspection and test on the new installation should be conducted(1 Mark) i) the status of those involved in the design, construction and verification of this(1 Mark) installation22 List a) FIVE relevant items from the inspection schedule(5 Marks) b) FIVE relevant tests (in sequence) to be conducted(5 Marks) c) the instruments to be used in b).(5 Marks)23 a) Give TWO reasons why a pvc conduit installation is preferable to a galvanised system(2 Marks) b) Indicate the bonding requirements for this complex.(2 Marks) c) Suggest why the light switch for each stable is externally located(2 Marks) d) Suggest, with reasons, a suitable IP rating for the external accessories.(4 Marks) e) Explain why, even though this is a T N-S system, 30 mA and 500 mA rcd's have been used(5 Marks)See next page 24 Briefly describe how a) a cpc continuity test would be conducted on the SWA supply cable to the complex(4 marks) b) an insulation resistance test would be conducted on circuit 5(4 marks) c) an RCD test would be conducted on the 100 A / 500 mA main switch(3 marks) d) an RCD test would be conducted on the 30 mA circuits(4 marks) (State actual test values and max, tripping times for c) and d))25 Indicate, using the rule of thumb (showing all workings) a) the calculated value of Zs for the distribution circuit supplying the complex(3 marks) b) the calculated value of Zs for each final circuit(5 marks) c) if each final circuit is acceptable,(7 marks)26a) Draw a labelled diagram of the earth fault loop path for the distribution board in the complex (7 marks) b) Calculate the prospective earth fault current at i) the intake position in the house (2 marks) if) the complex distribution board, (2 marks) c) Explain i) why there is a difference between the two values in b) (2 marks) ii) the difference between prospective short circuit current and prospective earth fault current(2 marks)


Jul 23, 2017
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