2330 level 3 smartscreen questions/answers

[m4tty]

#SmartScreen

Level 3 Certificate in Electrotechnical Technology Unit 2 Sample questions answers

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#Unit 2: Installation (Buildings and Structures): inspection, testing and commissioning

Sample questions

Answer guide

1. List three widely used types of:

a. wiring system

b. wiring enclosure

Solution

a. micc cable

PVC/SWA cable

XLPE/SWA cable

PVC twin and earth cable

fire retardant cable (any 3) (3 marks)

b. PVC trunking

steel trunking

PVC conduit

steel conduit

ducting (any 3) (3 marks)

2. When making an area safe to work in

a. list three procedures to be taken before commencing work

b. describe the permit to work procedure

Solution

a. Use barriers and tapes to cordon off the area.

Place warning signs in appropriate positions.

Isolate equipment from the supply. (3 marks)

b. The permit to work is a formal procedure in the form of written authorisation used to control work in potentially hazardous areas. (3 marks)

3. When carrying out large contracts

a. list three parties likely to be concerned

b. state the purpose of a site record

Solution

a. Client

Contractor

Supplier

Consultant

Sub contractor (any 3) (3 marks)

b. Provides a continuous, updated record of all activities on site.

4. Describe the use of the following in monitoring the progress of a contract

a. a bar chart

b. a site diary

c. variation orders.

Solution

a. To display progress of different parts of a contract graphically. (2 marks)

b. A daily record of events on site. (2 marks)

c. Variation orders are requests for extra work or change to a contract and must be given in writing. The issue of variation orders may affect the main contract progress. (2 marks)

5. With reference to the application and use of residual current devices (RCD)

a. list three situations where R.C.D. protection is required

b. state the primary function of an R.C.D.

c. describe the term nuisance tripping.

Solution

a. For sockets installed on TT earthing systems.

For socket outlets likely to supply portable equipment used out of doors.

Where satisfactory values of Zs cannot be achieved. (2 marks)

b. To limit the severity of electric shock. (2 marks)

c. When tripping occurs due to small leakage currents that do not constitute a real fault. (2 marks)

6.

a. Explain briefly the importance of verification of test instruments before performing tests on an electrical installation.

b. State the purpose of each of the following types of test instrument

i) Insulation Resistance tester

ii) Tong tester

iii) PSCC tester

iv) low ohm reading meter

Solution

a. Verification of test instruments ensures that the meter to be used is functioning correctly and test measurements will be accurate. (2 marks)

b. i) To measure insulation resistance between conductors.

ii) To measure current in a conductor without breaking the circuit.

iii) To measure the prospective short circuit/Earth fault current in a circuit.

iv) To check the continuity of ring circuits or continuity of protective conductors or dead polarity.

(4 marks)

7. A 10 kW 230v shower is supplied using PVC/ PVC multicore cable clipped direct

to the surface over a distance of 15m. The circuit is protected by a BSEN 60898

type C circuit breaker. The ambient temperature is 25 deg C.

Determine

Installation method

Design current

Circuit breaker rating

Correction factor

Minimum cable size

Voltage drop

Solution

Method 1 (Table 4A1)

43.5

45A or 50A depending on source material used

1.03 (Table 4C1)

6mm or 10mm (see c above)

4.76v or 2.871v (see c above)

Identify three items to be checked during the initial inspection process for

steel conduit

steel trunking.

Solution

a. Ensure conduit is securely fastened to building fabric, stress is not placed on the conduit, all fittings are tight to provide a good earth path, conduit capacity is not exceeded, no sharp edges, bushes tight, exposed threads painted over etc. (3 marks)

b. Correct bonding at joints using copper bonding strips, circuit segregation provided if necessary, space factor of the trunking not exceeded, covers fixed correctly etc.

(3 marks)

9. When completing additions to a circuit such as an extra socket

a. state the type of certificate to be issued

b. list three items of information that need to be entered on the form

c. state to who the form should be given.

Solution

a. A minor works certificate. (2 marks)

b. Details of the existing installation.

Description of the minor works.

Test results. (3 marks)

c. The person ordering the work. (1 mark)

10. Describe briefly the purpose and types of information which relate to the electrical installation of the following types of drawing

a. site plan

b. block diagram

c. circuit diagram.

Solution

a. A site plan will show the general layout of buildings and structures on a construction site. The types of information which relate to the electrical installation are layout of sub-stations and distribution cables routes. (2 marks)

b. A block diagram shows the relative position of components within an electrical installation without detail. Its purpose is to provide an uncomplicated view of the interconnection of electrical components within an electrical system. (2 marks)

c. A circuit diagram provides details of circuits and control equipment. It is used to show the specific components used within an electrical system. (2 marks)

11.

a. Explain the importance of coordinating electrical installation contracts with

other trades.

b. Describe one example where joiners/carpenters may be held up due to lack of

coordination with electricians working on the same site.

c. Describe one example where plasterers may be held up due to lack of

coordination with electricians working on the same site.

Solution

a. General construction work requires coordination between different trades to ensure that the work proceeds without delays and that minimum disruption is caused by workers from different trades appearing on site at the same time and working in the same area. Also helps ensure safe working environment. (2 marks)

b. Joiners/carpenters may be ready to lay down floorboards where the electrician has not installed cables which are required to run under the floorboards.

(2 marks)

c. Plasterers may be delayed by the electrician who has not completed a first fix of cables, sockets and switches to the wall where the cables are required to be concealed within the plaster. (2 marks)

12.

a. With the aid of a sketch, show how a 230V single phase supply and a 400V 3 phase supply is produced within a sub-station using a transformer with delta connected 11kV primary windings and star connected secondary windings.

b. State two reasons for balancing the loads across a 3 phase 4 wire system.

Solution

a. (4 marks)





b. The loads should be balanced to ensure

i) the neutral current is kept to a minimum

ii) the cable size is kept to a minimum

iii) optimum use is made of transformer capacity

iv) switchgear sizes are kept to a minimum.

any 2, or other suitable alternatives

(2 marks)

#SmartScreen

Level 3 Certificate in Electrotechnical Technology Unit 2 Sample questions 2 answers

#Unit 2: Installation (Buildings and Structures): inspection, testing and commissioning

Sample questions 2

Answer guide

1 (1.5.d, 1.1.e, 1.3.b/c)

a. Identify the statutory regulations which recommend that except for special circumstances, work should not be carried out on live electrical systems.

b. State who issues, and the purpose of, a

 

[m4tty]

Solution

a. Environment, utilisation, building. (3 marks)

b. Any from Appendix 5, BS 7671 as applicable to each sub-section. (3 marks)

3. (1.6.B)

A 100A single phase TT system is used to supply a 32A ring final circuit and a 6A lighting circuit using a split load board fitted with type C circuit breakers.

Draw a block diagram to indicate the sequence of supply, metering and control from the intake up to and including the circuit breakers.

Solution

Answer similar to above or as On-site Guide.

A = Service head.

B = Meter.

C = Main switch

D = 30mA RCD

E = 32A CB

F = 6A CB.

(1 mark each, NO marks if incorrect sequence)

4. (1.11/12)

a. State the typical voltage(s) that would be found on the following sections of the Electrical Network.

i) Primary output from a typical power station.

ii) Grid system.

iii) Ring main distribution to the primary of a local feeder transformer.

b. With the aid of a drawing show how a three-phase 400v 4 wire supply and a 230v single phase supply may be obtained from a delta/star transformer.

Solution

a. i) 25 kV. (1 mark)

ii) 275 or 400 kV (1 mark)

iii) 11 kV (1 mark)

b. Any suitable drawing showing delta/star transformer (1 mark)

three-phase and neutral output or load (1 mark)

single-phase and neutral (1 mark )

5. (1.13)

Identify the device(s) used in a 400A three-phase four-wire 400v installation (TN-C-S) with a rated short circuit at the intake of 46kA to provide

a. overcurrent protection

b. earth fault protection

c. isolation.

Solution

a. Cartridge fuses to BS 88 or moulded case circuit breakers (2 marks)

b. Residual Current Device (2 marks)

c. Fused switch (2 marks)

6. (1.15a/b)

Identify a suitable wiring system for each of the following.

a. Rewire of a domestic installation where chasing of the walls is not allowed.

b. Blocks of offices provided with raised floors and false ceilings.

c. Stable blocks fitted with internal and external lighting.

Solution

a. PVC/PVC surface fixed or in mini-trunking.

b. Basket with suitable wiring for final circuit types (pvc /pvc/FP 200 gold etc).

c. High impact PVC conduit with single core cables.

or suitable alternatives (3 x 2 marks)

7. (1.19. a-d)

A 230v, 6 kW single phase load is supplied by single core pvc cables in high impact pvc conduit fixed to the surface of a brick wall over a distance of 20 metres. The circuit is protected by a type C circuit breaker. The temperature is 35 degrees Celsius.

Determine

a. the design current

b. the installation method

c. the circuit breaker rating

d. the correction factor

e. the minimum cable rating

f. the minimum cable size.

Solution

a. 6000 / 230 = 26A

b. From table 4A1 method 3

c. 32A

d. From table 4C1 0.94

e. 32/0.94 = 34 A

f. From table 4D1A col 4. 6mm2 41A (6 marks)

8

Identify three methods from BS 7671 2008, which provide basic protection from electric shock.

( 3 x 2 )

Any from Insulation, Barriers and enclosures, obstacles or placing out of reach.

9. (1.22)

Explain the terms

a. earthing

b. bonding.

Solution

a. Earthing: connection of the exposed conductive parts of an installation to the main earthing terminal of that installation. (3 marks)

b. Bonding: connection of the extraneous conductive parts to prevent a difference of potential between them. (3 marks)

10. (1.24. b/c/d)

For each of the following devices, state a limitation with respect to

a. re-wireable fuse used on a circuit with a 16 kA fault current

b. circuit breakers used for basic protection

c. residual current devices used to protect multiple IT circuits.

Solution

a. Rewireable fuses have a breaking capacity of up to 4 kA so are unsuitable for a 16kA fault current. (2 marks)

b. Circuit breakers will not work on the small current flowing due to electric shock. situation. (2 marks)

c. The aggregate earth leakage current of the various circuits will cause nuisance tripping. (2 marks)

11. (2.1.a)

State

a. three reasons for the initial verification procedure for a new installation.

b. three forms to be filled in at the completion of an initial inspection and test of a new installation.

Solution

a. i) Complies with section 511.

ii) Correctly selected and erected.

iii) Not visibly damaged or defective. (3 marks)

b. Electrical Installation Certificate.

Schedule of Inspections.

Schedule of test results. (3 marks)

12. (2.7.a)

Describe how to carry out a continuity of protective conductors test on a lighting circuit fitted with Fluorescent luminaires.

Solution

a. Isolate supply and prove dead

b. Link phase and cpc at distribution board

c. Null test leads or record resistance of leads

d. With low reading ohm meter test between phase and cpc at luminaries

e. Operate switches to prove circuit

f. Reinstate circuit and record results. (6 marks)

13. (2./5c 7.B)

An insulation resistance test is to be carried out on a 230v 8-way distribution board fitted with type B circuit breakers. One of the lighting circuits has a dimmer switch included.

a. State the type of instrument to be used, the test voltage and current

b. Precautions to be taken before carrying out the test on the board

c. The minimum acceptable insulation resistance for the Board

Solution

a. Insulation resistance tester, 500v d.c, 1mA (3 marks)

b. Disconnect the dimmer switch or test with phase and neutral linked testing to earth.

(1 mark)

c. 1.0 M ohm. (2 marks)

14. (2.8)

The following test results are obtained when carrying out a test on an electrical installation.

State whether the values comply with BS 7671 17th Edition wiring regulations and the reason for your answer.

Number Test Test results

1 Insulation resistance of SELV circuit 0.4 M ohm

2 Earth loop impedance test 32A type B circuit breaker, Industrial Installation 1.8 ohm

3 Test on 30mA rcd @ 5 x rating 20 mS

4 Test on 30mA rcd @ 0.5 x rating 100 mS

5 Earth Loop impedance test on 32A BS 88 cartridge fuse protecting a socket. 0.8 0hm

6 Continuity of Protective conductor Infinity.

Solution

Number Answer Rationale

1 Complies Value above 0.25 M ohm

2 Fails Value above 1.5 ohm

3 Complies Value below 40 mS

4 Fails Should not trip

5 Complies Below 1.04 ohm

6 Fails Value expected to be very low, infinity indicates open circuit

(6 marks)

15. (2.9.a/b)

a. State who is responsible for deciding the date of the next test of an installation at the initial verification, inspection and testing stage.

b. State who is responsible for deciding the date of the next test after a periodic inspection and test.

c. Identify two occasions when a minor works electrical installation certificate would be issued.

Solution

a. The designer (2 marks)

b. The person carrying out the inspection and test (2 marks)

c. Adding a new socket or luminaire, replacing like for like, replacing a run of cable along the same route. (any 2 x 1 mark)

16.

A schedule of test results is to be completed for a ring final circuit. The resistance values of the phase and CPC loops are measured as 0.6Ω and 1Ω respectively. The value of Ze is 0.35Ω.

a. Determine the expected value of R1 + R2 to be compared with the test reading

b. Determine the expected value of Zs

c. Indicate the symbol to be inserted on the schedule of test results for the ring final circuit only.

Solution

a. 0.6Ω + 1Ω = 0.4Ω (2 marks)

4

b. 0.35 Ω + 0.4 Ω = 0.75 Ω. (2 marks)

c. Usually a tick or other symbol to indicate that the circuit is a ring final circuit.

(2 marks)

 

[unshockable]

This looks really good, i am at colchester institute in my second year, i have completed the practical exam and have the online tests to do shortley, has anyone got the online test/answers, i hope so, i really need to pass it and it just seems so much to remember

steve

 

[S60TEM]

how do you get access to smartscreen? I'm doing my course through OLCI but they havn't got access to it. Anyone?

 

[m4tty]

You could try ringing OLCI as they must be registered with C&G. They should give you a centre number and a password. A few of the other training providers use ATL for their practical training and they gave me smartscreen access.

 

[banny07]

thanks m4tty for very useful info.. could you please post more.

 

[oktay]

need i say how awesome this is?

 

[Manator]

I will have a word with Admin to see if we can consolidate this and move it to the downloads section.

 

[Peter73]

I done my exam and passed last month and a lot of the questions here where in my paper,

wish i had found this forum sooner.