2391 Theory Test Paper

[r10ley]

Hi all, I got given a past exam paper from the 2391 course tutor however it doesnt come with any answers so I thought id put the question and my answers on here to see if im going down the right track and also to help anyone else taking this course so please correct me if im wrong because I probably am.

Q1. BS 7971 requires an inspection to be made on installed electrical equipment during the initial verification. State the three areas to be verified.

A1. .All electrical equipment and materials are of the correect type and comply with all relavent British Standards
.All part of the fixed installation are correctly selected and erected
.No parts of the fixed installation is visually damaged or otherwise defective

Q2. a) Two items of information regarding the protective device at the origin, to be obtained from the distribution network operator.
b) What the designer may take into account when determining maximum demand

A2. a) The rating of the device and its rated short circuit capacity
b) The full load of the installation with diversity applied

Q3. State one statutory and two non statutory publications which relate directly to the inspection and testing process

A3. Statutory - Electricity at work regulation, Non Statutory - BS7671 and Guidance note 3

Q4. A steel conduit and trunking installation has been erected and is to be inspected prior to the installation of cables. State three inspection items which will be checked using the sense of touch.

A4. No sharp edges, conduit is reamed and bushed
Trunking lids are secure
All conduit trucking and accessories are securely fixed

Q5. The electrical installation in a sandwich bar is to be inspected and tested in order for the owner to obtain a license from the local authority. State
a) the two parties with whom the inspector must discuss the requirements for the inspection and test
b) where the outcome of the discussion is to be recorded

A5. a) The local authority and the sandwich bar owner
b) On the periodic inspection report form under extent of installation inspected and limitations.

Q6. List three operational characteristics of a low resistance ohmmeter as identified in guidance not 3.

A6. .No load voltage between 4V and 24V
.Short circuit current not less than 200mA
.Test current a.c and d.c

Q7. a)State two reasons for the prescribed sequence of test prior to energising a new circuit.
b)State one test on an installation forming part of a TT system which may be carried out as either a live test or a dead test.

A7. a)To ensure that the polarity is correct and that no short circuits exist on the installation prior to energising it.
b) Resistance of the earth electrode (Ze)

Q8. State one method of verifying each of the following (each method must be different)
a)Continuity of a lighting circuit CPC
b)Continuity of a main protective bonding conductor 40m in length
c)Continuity of the earthing conductor

A8. a)R1 +R2 test
b)Wandering lead test
c) Ze test

Q9. A conductor of length 50m has a resistance of 2.3mohms/m. A second identical conductor is to be installed in parallel with this conductor. Determine the total resistance of these two conductors when connected in parallel. Show all calcs.

A9. Resistance of conductor = (2.3 x 50)/1000 = 0.115
1/RT = 1/R1 + 1/R2
1/RT = 1/0.115 +1/0.115
1/RT = 17.4
RT = 1/17.4
RT = 0.057 or 57mohms

Q10. State a)two factors which will reduce the insulation resistance of a new installation measured at the distribution board with all the circuits connected.
b)the voltage to be applied when testing the insulation resistance of a 400V ac circuit

A10. a) Number of circuit connected in parallel
b) Length of circuit (decrease when longer)

Q11. A circuit which includes surge protection devices is to be tested to determine insulation resistance. State
a)two methods recognised in BS7671 for safely testing this circuit
b)the minimum test voltage which can be applied

A11. a) Remove surge protection and link out or if not possible test with reduced test voltage
b)250V dc

Q12. An insulation resistance test is carried out on each of the following circuits. State the test voltage to be used in each case.
a)25V SELV lighting circuit
b)650V three-phase motor circuit
c) 110V reduced low voltage circuit

A12. a)250V DC
B)1000V DC
C)500V DC

Q13. State three special locations identified in BS7671 which are divided into zones

A13. Swimming pool, Area containing a bath or a shower, A sauna

Q14. State the appropriate IP protection to be provided for the
a)top surface of a readily accessible motor starter
b)front of a readily accessible distribution board
c)internal barrier within a consumer unit where the cover can be removed without the use of a tool or key

A14. a)IPXXD
b)IPXXB
c)IPXXB

Q15. A BS 1361 fuse is to be used to provide overcurrent and fault protection for a new circuit. State the effect on the operation of the fuse when the following conditions occur if the fuse was installed in the neutral conductor,
a)overload fault
b)earth fault
c)short circuit fault

A15. a)Fuse will operate however the supply will not be cut off
b) The fuse will not operate
c) The fuse will operate but the supply will not cut off

Q16. State a)The test instrument used to measure the earth electrode resistance for
i/ a generator
ii/ an installation protected by an RCD and forming part of a IT system
b)the number of readings to be taken for the test in a)i/ above.

A16. a) i/Earth electrode resistance tester
ii/Earth loop impedance tester
b) 3

Q17. State a)two methods by which the external earth fault loop impedance (Ze) may be determined
b)one method of determining Zs when direct measurement is not possible (Not Ze)

A17. a)Driect measurement and enquiry
b)Calculation Zs=Ze+(R1+R2)

Q18. State the maximum permitted time/current performance criteria for a 30mA BS EN 61009 RCBO when tested at
a)15mA
b)30mA
c)150mA

A18. a) No trip
b) 300 ms
c) 40 ms

Q19. a) List the two test measurements to be taken in order to determine PFC at the origin of a single phase electrical installation
b) State which of the measured values is to be recorded

A19. a) Prospective earth fault current and Prospective short circuit current
b) The higher of the two

Q20. State three locations in an electrical installation where phase sequence would need to be confirmed

A20. Origin of installation, At the distribution board, At end of final circuit supplying a motor

Well thats the first 20 questions and my fingers are abit sore now lol. My only problem with this course is that some of the questions are so ambiguous half the time I know the answer just cant understand what the question nis answering me. So please if any of my answers are wrong let me know

Thanks

r10ley

 

[brucelee]

Hi mate these are the questions from june 2009 exam I thought they rang a bell lol as i did this exam

 

[r10ley]

Yeah they are couple of the questions are abit of a pig I thought lol. Suppose you can pass all the past papers you want its the one you get on the day that count. O well practicle tomorrow so im going to forget the theory for a couple of days lol.

Cheers for your help

r10ley

 

[SMB]

The more past papers you do the easier the exam will be. Especially the first 20 questions.

Do as many past papers as you can get your hands on.

Understand the earth fault loop diagram for all systems.

Understand continuity of the ring final circuit testing.



Good luck with your practical.

 

[brucelee]

Hi mate good luck you have done ok with most of your answers but use correct terminlology as they will pick you up on it use what is wrote in GN3 and for the continuity of ring final circuits do it in 3 steps
step 1 End to End
step 2 cross connect Line and Neutral
step 3 cross connect line and CPC

do as SMB says and get exam success as many Pat papers you can
cristopher kitchers guide to inspection and testing is a good book and its cheap from amazon think it was £11.55 last time i looked I have loads of books i bought
and this was the one which explained it in easier terms
GN3 is the bible though as this is what its based on
also get acopy of GS38 learn that
memorandum of guidance on Electricity at work regs 1989

and when naming stat and non stat docs use for example

stat
health and safety at work act 1974
Electricity at work regulations 1989
non stat
Guidance Note 3
On- Site Guide
BS7671 or the requirments for electical installations

Safe isolation procedure
tests in sequence
learn how to explain in bullet points to save time with or without diagrams
and as you have above with calcs for the continuity of ring final circuits

from what I have read you shouldnt go far wrong mate

Good luck

 

[Deleted member 26818]

Would you include Part P 2006/10 as statutory in relation to domestic installations?
What about CDM Regulations?

 

[brucelee]

No mate dont think so
this doesnt come up on the 2391 well didnt when i did it last year just the usual ones above

 

[r10ley]

Hi all passed me practical today was easier than I thought it would be yipee. Thanks all for your input ill follow it and keep my fingers crossed!

Thanks

r10ley

 

[Jurasic Spark]

Would you include Part P 2006/10 as statutory in relation to domestic installations?
What about CDM Regulations?

The Building Regs' 2000 is Statutory and all the Approved Docs' included Part P are guidance (and therefore NonStat') on how to comply.

 

[r10ley]

Hi all again. Got my hands on another past paper without answers again so I thought id put it up on here to get some feedback and to help others again.
Q1. List 3 installation details that must be recorded, as identified on a Minor Electrical Installation Works Certificate (3 Marks)
A1.
.Type of earthing arrangement
.Method of fault protection
.Prospective device for modified circuit

Q2. State, for each of the following, if the documents are statutory or non statutory.
a) BS 7671 (1 mark)
b) Guidance Note 3 (1 Mark)
c) Electricity at Work Regulation (1 Mark)

A2.
a) Non Statutory
b) Non Statutory
c) Statutory

Q3. State three items of information, relating to the incoming supply for an electrical installation, that must be recorded on a schedule of test results. (3 Marks)

A3.
.Type of earthing arrangement
.External earth fault loop impedance (Ze)
.Prospective fault current (PFC)

Q4. State three general requirements against which installed equipment must be confirmed when carrying out an initial inspection, as stated in BS7671. (3 Marks)

A4.
.All electrical material and equipment is of the correct type and complies with all relevant British standards
.All parts of the fixed installation are correctly selected and erected
.No parts of the fixed installation are visibly damaged or defective so as to impair safety

Q5. List three non compliances that may be identified during the inspection process using the sense of touch. (3 Marks)

A5.
.Boxes and enclosures not securely fixed
.Terminations of conductors arnt tight
.Conductors overheating because they are underrated

Q6. A test for continuity of protective conductors is required as part of a initial verification on an installation. State
a)What must be confirmed when testing a radial socket-outlet circuit (1 Marks)
b)How the recorded measured value is to be confirmed as satisfactory (1 Mark)
c)One factor that may affect the measured values obtained (1 Mark)

A6.
a)Polarity
b)Added to Ze (Zs=Ze + (R1+R2)) then compared to amended BS7671 values
c)Ambient temperature

Q7. A test is carried out to obtain an R1+R2 value at the furthest point of a two-way lighting circuit. Explain why it is necessary to operate the two way switching during the test. (3 Mark)

A7. To confirm polarity and to ensure there are no breaks in the switch wiring

Q8. A test for continuity of ring final circuit conductors is to be carried out on a circuit containing no spurs. State.
a)the expected value of R1+R2 for the circuit if the resistance of the line, neutral and cpc loops are 0.2ohms, 0.2ohms and 0.33 ohms respectively. (2 Mark)
b)The effect on the circuit R1+R2 value if a non fused spur supplying a socket-outlet was added to the circuit (1 Mark)

A8.
a)R1+R2 = (r1+r2)/4 = (0.2+0.33)/4 = 0.13
b)It would increase R1+R2 as the cabling supplying the spur would be added.

Q9. Following repairs to a motor and before its reconnection, an insulation resistance test is to be carried out on a securely isolated three phase motor circuit. State
a)The two tests to be carried out in order to complete the schedule of test results in BS7671
(2 Marks)
b)How the cable between the motor starter and the motor maybe included in the test in a)
(1 Marks)

A9.
a)Between live conductors (Live/Live) and between Live conductors and Earth (Live/Earth)
b)Link across the motor starter

Q10. An insulation resistance test is to be carried out to confirm electrical separation of one circuit from another circuit contained in the same conduit. State
a)test connections required to confirm electrical separation (2 Marks)
b)minimum acceptable value of insulation resistance (1 Mark)

A10.
a) Between separated circuit conductors connected together and other circuit conductors connected together. Between separated circuit conductors and earth
b) Tested at 500V DC and greater than 1Mohm
Q11. State three methods of providing protection against electric shock for a 16A socket-outlet circuit installed on a construction site (3 Marks)
A11.
.Insulation of live parts
.Automatic disconnection of supply
.Additional protection via a 30mA residual current device

Q12. State the IP codes for enclosures that provide protection against a
a)12.5mm diameter sphere (1 Mark)
b)British standard finger test only (1Mark)
c)1mm Diameter wire (1 Mark)

A12.
a)IP2X
b)IPXXB
c)IP4X

Q13. State the test carried out to confirm that
a)the outer screw contact of an Edison screw type lamp holder is connected to the neutral conductor (1 Mark)
b)a lighting circuit protective device will disconnect within 0.4s in the event of an earth fault
(1 Mark)
c)a fuse protecting an electrical installation will operate safely in the event of a short circuit fault
(1 Mark)

A13.
a)Polarity test
b)Earth fault loop impedance
c)Prospective fault current

Q14. A test is to be carried out on a earth electrode, using an earth electrode resistance tester. State
a)Why it is necessary to take readings with the centre electrode in three different positions (1 Mark)
b)How to determine the electrode resistance if the three readings in a) above are similar in value
(1 Mark)
c)Another type of test instrument that may be used to carry out this test when the electrode being tested forms part of a TT system and is protected by an RCD (1 Mark)

A14.
a)To ensure the resistance area doesn’t overlap
b)Take the mean of the three readings
c)Earth fault loop impedance tester

Q15. State, for each of the following, the type of system used for public supplies thathas an earth return path, external to the installation consisting of,
a)a PEN conductor (1 Mark)
b)the general mass of earth (1 Mark)
c)separate neutral and protective conductors (1 Mark)

A15.
a) TN-CS
b) TT
c) TN-S

Q16. An earth loop impedance test is to be carried out on a healthy ring final circuit consisting of nine socket-outlets connected directly in the ring. State the,
a)instrument to be used (1 Mark)
b)pattern of test results when carrying out the test at each socket outlet around the ring (1 Mark)
c)value to be recorded on the schedule of test results (1 Mark)

A16.
a)Earth loop impedance tester
b)Should increase slightly as you move closer to the middle of the ring and then decrease again
c)The highest reading taken

Q17. State,
a)one condition where BS7671 requires a 30mA RCD to provide additional protection to a circuit in a office (1 Mark)
b)the maximum permitted disconnection time of the RCD in a) above, when a current of 150mA flows to earth (1 Mark)
c)The maximum permitted earth loop impedance of a circuit forming part of a TT system if it is protected by a 300mA RCD (1 Mark)

A17.
a) Any socket outlet up to 20A that may be used by ordinary persons for general use
b) 40ms
c) Ra = 50/300mA = 167ohms

Q18. State the,
a)effect on the value of prospective fault current when it is measured within the installation at increasing distances from the origin (1 Mark)
b)two types of fault that must be considered on a single phase TN-S system when considering an installation PFC. (2 Mark)

A18.
a)It will decrease
b)Prospective earth fault current and Prospective short circuit current

Q19. State three factors that may affect the measured earth fault loop impedance value of a circuit, excluding final circuit conductor length and cross sectional area. (3 Mark)

A19.
.Ambient temperature
.Electrical Loading
.Being surrounded by insulation

Q20. State the maximum permitted percentage voltage drop for each of the following circuits supplied directly from a public low voltage distribution system.
a)230V lighting circuit (1 Mark)
b)Three-phase 400V motor circuit (1 Mark)
c)Distribution circuit supplying a single phase distribution board (1 Mark)

A20.
a)3%
b)5%
c)5%

The only thing I think im not sure about is in question 10 would you include a test between the separated circuits exposed conductive parts and the cpcs and exposed conductive parts of other circuit?

Thanks

r10ley

 

[Deleted member 26818]

Question 6,a) is incorrect.
You are testing the continuity of protective conductors, it is the live conductors where polarity must be confirmed, the clue, is that in question b), you are adding the recorded measured value from a) to Ze.
Question 17,a) Is also incorrect.
There is no requirement in BS7671 for an office circuit to be RCD protected, unless the office is in or forms part of a special location.
The requirement to RCD protect any socket-outlet intended for general use by ordinary persons, applies only to the socket-outlets, not to the circuit supplying them.
Question 19,c), I doubt the pressence of thermal insulation, will affect the measured value.
Question 10, I would only test between the Live conductors of one circuit, and those of the other to prove separation.

 

[r10ley]

Thanks for your feed back reading 6 a) I can see my mistake need to read question a bit more carefully. As for 17 a) can you help me with the answer im struggling : (

Thanks

r10ley

 

[kennydeeee]

17A sockets for use by unskilled persons in office could be cleaners sockets
or cables concealed in wall less than 50mm deep

 

[Deleted member 26818]

17A sockets for use by unskilled persons in office could be cleaners sockets
or cables concealed in wall less than 50mm deep

The question asks for "one condition where BS7671 requires a 30mA RCD to provide additional protection to a circuit in a office".
Neither of the above applies to circuits whether they be in an office or otherwise.
The only situation where 30mA RCD protection for circuits is required by BS7671 is in relation to special locations.
As such the answer should be when the office is part of an installation on agricultural/horticultural premises, or is itself a transportable unit, such as a portacabin.

 

[r10ley]

Thanks again makes sense, can you help me with this one im not sure about my answers.

Q. Four operational considerations relating to a electrical installation that must be discussed in order to agree the limitations and plan the work. (8 Marks)

A.
. When each part of the installation can be isolated
. Any items of equipment which cannot be disconnected/linked out
. When it is safe to perform certain testing as not to present danger to people
. What percentage of the installation the client would like to be inspected

Thanks

r10ley

 

[kennydeeee]

The question asks for "one condition where BS7671 requires a 30mA RCD to provide additional protection to a circuit in a office".
Neither of the above applies to circuits whether they be in an office or otherwise.
The only situation where 30mA RCD protection for circuits is required by BS7671 is in relation to special locations.
As such the answer should be when the office is part of an installation on agricultural/horticultural premises, or is itself a transportable unit, such as a portacabin.

Im sure u will find in bs7671 2008 the definition of a circuit and a socket outlet would be classed as part of the circuit not just the cable supplying it.

If for example the sockets where for use by the unskilled person additional protection would be required 30 mA rcd to the nessesary part of the circuit in this case the sockets. If the circuit meets
reg 522.6.6 - 522.6.8 then the socket outlets could be 30mA socket outlets if not the rcd would need to be at the origan of the circuit at (dist board)

circuit (assembly of electrical equipment)

As for cables burried in walls in office or anywhere else not under the supervison of a skilled person reg 522.6.6 - 522.6.8

so either 1 of these would be suitable answers