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

 

[Deleted member 26818]

In this respect, the Regulations are unusually quite precise.
Despite the fact that both socket-outlets and cables are parts that would go towards making up a circuit, there is no requirement in BS7671 for the whole circuit to be RCD protected when these parts require RCD protection.
The question is in relation to a circuit in an office, part of an installation where BS7671 would not normally expect ordinary persons to have access to any socket-outlets, and would expect the installation to be under the control of a skilled or instructed person, as such there would not normally be a requirement for RCD protection, unless a socket-outlet is used to power mobile equipment outdoors, and even then such would not require the whole circuit to be RCD protected.
The only references in BS7671 to circuits requiring RCD protection are in relation to special locations.
You would not normally expect there to be a bath or a shower in an office, so the only special locations that would be applicable to my mind would be those for agricultural/horticultural or transportable units.

 

[topquark]

Regulation 522.6.7 applies as a follow on from 522.6.6. A cable concealed in a wall or partition at a depth of less than 50 mm from a surface of the wall or partition.

 

[kennydeeee]

In this respect, the Regulations are unusually quite precise.
Despite the fact that both socket-outlets and cables are parts that would go towards making up a circuit, there is no requirement in BS7671 for the whole circuit to be RCD protected when these parts require RCD protection.
The question is in relation to a circuit in an office, part of an installation where BS7671 would not normally expect ordinary persons to have access to any socket-outlets, and would expect the installation to be under the control of a skilled or instructed person, as such there would not normally be a requirement for RCD protection, unless a socket-outlet is used to power mobile equipment outdoors, and even then such would not require the whole circuit to be RCD protected.
The only references in BS7671 to circuits requiring RCD protection are in relation to special locations.
You would not normally expect there to be a bath or a shower in an office, so the only special locations that would be applicable to my mind would be those for agricultural/horticultural or transportable units.

as i said cleaners sockets in an office for general purpose a cleaner would not be a skilled person the cleaner would be hovering after hours so would not be under any supervision from a skilled person so the sockets would would require additional protection.



I dont really care anymore i done this paper as a mock exam got this question marked right and got 90%

 

[Deleted member 26818]

as i said cleaners sockets in an office for general purpose a cleaner would not be a skilled person the cleaner would be hovering after hours so would not be under any supervision from a skilled person so the sockets would would require additional protection.

I dont really care anymore i done this paper as a mock exam got this question marked right and got 90%

There are exceptions for some of the Regulations requiring RCD protection in BS7671. Primarily these exceptions apply to commercial/industrial installations where the Electricity At Work Regulations apply.
Here is the entirity of Regulation 16 of EAWR 1989 "No person shall be engaged in any work activity where technical knowledge or experience is necessary to prevent danger or, where appropriate, injury, unless he possesses such knowledge or experience, or is under such degree of supervision as may be appropriate having regard to the nature of the work."
This Statutory requirement, entails that anyone (including cleaners) using a socket-outlet as part of their work duties must meet the criteria for a skilled or instructed person as defined in BS7671.
As such there is no requirement in BS7671 for cleaner sockets to be RCD protected, unless that socket-outlet is used for mobile equipment outdoors, or is in a special location
Now I don't know who marked your mock exam, or what answer you gave for this particular question.
I doubt though from the information you have supplied, that if you had taken the December 2010 exam, that you would have got this question marked as correct.

 

[Flakey]

Hi i was looking at this old post and saw a calculation resolved which im not too sure is right and would apprciate confirmation wether it is or isnt
Q24. A continuity of ring final circuit conductors test is to be carried out on a circuit supplying the office. The circuit is wired in 2.5mm cable with 1.5mm cpc. The loop length of the cable is 65m. All socket outlets are connected directly on the ring. Explain in detail, using the information given in figure 1, the three steps required to confirm the continuity of this circuit.
Your explanation should include the
. test instrument
. test connections and the expected readings at each stage
Show all calculations

A24. The test instrument used is a low resistance ohm meter. First test is an end to end of the line neutral and cpc of the ring. This is confirm all conductors form a complete ring. The expected results are:

Line – line – 2.5mm cable = 7.41 mohm/m
(7.41x65)/1000 = 0.48 ohms

Neutral – Neutral – Same as above

Cpc – Cpc – 1.5mm = 12.1 mohms/m
(12.1x65)/1000 = 0.786 ohms

Next cross connect line and neutral of the ring L1 + N2 and L2 +N1 and test at all socket outlets
Expected readings:

R1+Rn = (r1+rn)/4 = (0.48+0.48)/4 = (0.24) ohm Do you use this figure in the stage 3 part of the calculation

Next cross connect line and cpc L1 + cpc2 and L2 + cpc1 and test at all socket outlets
Expected readings:

R1+R2 = (r1+r2)/4 = (0.48+0.786)/4 = 0.32 ohms so 0.24 + 0.786/4 = 0.25 ohm ?

Many thanks
James