2391 Theory Test Paper

[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

 

[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