2391-10 Revision question 1

[IQ Electrical]

2
An engineering works is 18 years old and is due for inspection and test. State the

​

a)
type of inspection and test required

(1 mark) ​

b)
documents that must be completed

(1 mark) ​

c)
circumstances under which the type of inspection and test in a) above may not be required.

(1 mark)​

Remember, the exact terminology MUST be used, it's so important to get into the habit of referring to each document and test instrument/procedure exactly as it appears in guidance Note 3.

 

[Paul.M]

Good question to start us off.......a) I knew the answer. b) I thought I knew the answer but would not have got full marks as I would not have written down the full wording. c) I had a guess and got it wrong. I've looked up this question after answering I and can safely say that I would only get 1 maybe 1.5 marks. How did john25 do?..... IQ, thanks for the time and effort, I look forward for the answers to mark my own attempt.

 

[malcolmsanford]

1. State the reason for undertaking a continuity test on the phase and c.p.c
conductors of a ring final circuit.

2. State TWO other tests automatically carried out when undertaking the above.

3. State four prerequisite checks that need to be applied prior to undertaking an
insulation resistance test.

4. State the danger that may arise if earth fault loop impedance tests are
undertaken prior to verifying the continuity of the c.p.c.

5. Name the THREE electrodes used when employing a proprietary tester to
measure the resistance of a rod – type electrode.

6. State FIVE items of technical information that are required to be completed on
an installation or periodic inspection and test report.

7. List THREE items of information relating to the incoming supply that should
be listed on the schedule of test results.

8. State the effect on insulation resistance of an installation if
a.additional circuits are added
b.circuits were disconnected/removed
c.the length of a 6A lighting circuit was extended

9. In the formula Zs = Uo/la what is represented by:

Uo
La
Zs​

10. State:
a) why it is necessary to remove one end of a bonding conductor
connection when verifying its continuity
b) the instrument used to verify continuity
c) a typical value of resistance when verifying the continuity of bonding
conductors

11. State why a factor 1.2 is applied to (R1+R2) when determining the total value
of phase and c.p.c conductor resistance of a final circuit.

12. State the possible outcomes if the factor of 1.2 was not applied to (R1+R2).


Answers sent in on a blank postcard to

Will post later

 

[Paul.M]

Ok Malcolm, ready for the answers. Don't think I'll be getting a gold star this time.

 

[malcolmsanford]

1 .to ensure that each ring is complete without interconnections

2. polarity / (R¹ + R²)

3 a) verify supply is isolated
b) disconnect any voltage sensitive equipment
c) all current using equipment disconnected
d) all local switched closed

4 possibility of shock from exposed and extraneous conductive parts

5. a)main electrode under test
b) potential electrode temporary
c) current electrode (temporary)

6.a)external impedance Ze
b) prospective fault current
c) earthing arrangements
d) maximum demand
e) rating of overcurrent device at the origin of the installation

7.
a)Zs at distribution boards other than at origin
b) prospective fault current
c) nominal voltage

8.a)insulation resistance decreases
b) insulation resistance increases
c) insulation resistance decreases


9. Uo- voltage to earth for TN systems
Ia - current causing operation of overcurrent device
Zs - impedance measures in ohms at the point in the circuit, which is furthest point origin of the supply

10. a) to avoid parallel paths
b) low – resistanc ohmmeter
c) less than 0.05 (50m )


11. a)to allow for increase in resistance with temperature rise
b)allows for increase in resistance from 20ºC to 70ºC

12.a)under phase to earth fault conditions the final value of impedance Zs may be greater than those tabulated in Tables 41
b) extended disconnection time resulting in the possibility of shock and or
fire.

 

[Paul.M]

Oh dear, just marked my own work. Need to try harder next time springs to mind. I lost a few marks due to terminology so must remember the correct terms for the exam. I've never worked on a tt earth rod before so that's an area to study. Ok all in all its better to know where your going wrong so I'm getting the books out. Thanks Malcolm for your time and effort, I'll get you a pint or two if you come to the charity golf day.

 

[malcolmsanford]

Bit of a jaunt from Saudi......................but the sentiment is appreciated. Yes I've banged on about terminology here before and it's quite amazing how so many people call a ring final circuit a Ring Main, these type of things put the markers off. I know that some will say sill ole f**t but it's the C&G ball game and they want you to use the right terminology and if you don't you get marked down.

Her is a scenario question then, sorry if it's long winded or been seen before, but hope it helps

A 15-year-old dry-powder coating factory is situated adjacent to an 11kV/415/240V Regional Electricity Company substation. The earthing system is T.N-C-S with an external earth fault loop impedance (Ze) of 0.012Ω and a prospective fault current of 20 kA.
The dry-powder coating process involves cleaning metallic components in an acid bath, washing off with water sprays, drying with hot air blowers, spraying with electrostatically charged powder and finally baking in a tunnel oven.
The existing installation, which are all radial circuits, is wired with (p.v.c.) conductors in metal conduit and trunking. Six new lighting circuits supplying high-bay 300W SON luminaires have been installed using a similar wiring system to the existing installation. The new circuit breakers are fed from a metal clad distribution board housing BS EN 60898 circuit breakers.
An inspection and test of the whole installation is to be carried out.

21
State
the type/s of overall inspection and test required (4 marks)
the certification/documentation that needs to be completed by the inspector (4 marks)
who should receive the originals of these documents (1 mark)
who decides when the first periodic test should be conducted on the new lighting (1 mark
One statutory and two non-statutory documents relevant to this inspection and testing process (3 marks)
the status of the inspector (2 marks)

State
apart from wear, tear and safety, five installation conditions that would need to be considered during the inspection process (5marks)

Five items from the BS 7671 schedule of inspections that would need to be considered ​

(5 marks)

Three human senses that would be used in the inspection process (3 marks)
with whom the extent and limitations of an inspection should be agreed (2 marks)​

List
the first four relevant tests, in sequence, to be conducted on the new lighting installation ​

(7 marks)

All relevant test equipment needed for a) (8 marks)​

24

Describe how an Insulation Resistance test would be carried out on the new lighting circuits (5 marks)
If an Insulation Resistance test between live conductors and earth on the whole installation resulted in a test value of 1.6MΩ, explain, giving reasons, any actions to be taken. (3 marks)
Describe how an external loop impedance test should be conducted. (4 marks)
Describe how a prospective fault current test should be conducted at the origin of the installation (3 marks) ​

25
The Maximum and measured values of loop impedance for four circuits are as follows

Max values Measured values
3.43 ohms 2.7 ohms ​

2.29 ohms 1.7 ohms
2.4 ohms 1.9ohms
3.75 ohms 3.2 ohms

Explain the reasons for the use of the ‘rule of thumb’ (3 marks)
Using the above method, determine if the measured values are acceptable. (Show all calculations). (4 marks)
For any circuit that fails to comply, indicate two methods of overcoming the problem.
(6 marks)

26
a)
Draw a labeled diagram of the earth fault loop path for any circuit in the installation.
8 marks)
Explain why it would be appropriate to use BS 3036 fuses in a distribution board at the origin of this installation (4 marks)
Most standard PSCC testers are designed for single-phase use. How could an appropriate value of short circuit current between phases be determined? (3 marks)

( ​

 

[IQ Electrical]

26
a)
Draw a labeled diagram of the earth fault loop path for any circuit in the installation.
8 marks)
Explain why it would be appropriate to use BS 3036 fuses in a distribution board at the origin of this installation (4 marks)
Most standard PSCC testers are designed for single-phase use. How could an appropriate value of short circuit current between phases be determined? (3 marks)

I think that should read 'explain why it would NOT be appropriate to use BS 3036 fuses'

 

[malcolmsanford]

I never noticed I left the "not" out ...........well spotted.

I can either put the not in ....or change it to BS 88 type ..........................thank you IQ

So leave it as why it would not be appropiate

 

[Paul.M]

Haven't had time to answer all but here goes.
1. Visual inspection with extra attention to circuits near to heat and the dry powder. Continuity of cpc + bonding. Continuity test. IR test.
2. PIR, schedule of test results, schedule of inspection, minor works cert for new installation.
3. The person ordering the work.
4. The inspector/tester.
5. (im think) eawr89.7671 and 2391.
6. Qualified and competent with experience of this type if work.
7. Water, damp, flora, forna, temperature, flammable eg petrol station, chemicals, dust eg bakery.
8. I'll come back to this one,
9. Sight, smell and touch.
10. The person ordering the work, the owner or the property.
11. Continuity of cpc, continuity of l + n, r1 + r2 test, IR.

I'll do the rest later when I have more time. Thanks Malcolm.

 

[Paul.M]

Haven't had time to answer all but here goes.
1. Visual inspection with extra attention to circuits near to heat and the dry powder. Continuity of cpc + bonding. Continuity test. IR test.
2. PIR, schedule of test results, schedule of inspection, minor works cert for new installation.
3. The person ordering the work.
4. The inspector/tester.
5. (im think) eawr89.7671 and 2391.
6. Qualified and competent with experience of this type if work.
7. Water, damp, flora, forna, temperature, flammable eg petrol station, chemicals, dust eg bakery.
8. I'll come back to this one,
9. Sight, smell and touch.
10. The person ordering the work, the owner or the property.
11. Continuity of cpc, continuity of l + n, r1 + r2 test, IR.

I'll do the rest later when I have more time. Thanks Malcolm.

 

[B6 7BU]

Bit of a jaunt from Saudi......................but the sentiment is appreciated. Yes I've banged on about terminology here before and it's quite amazing how so many people call a ring final circuit a Ring Main, these type of things put the markers off. I know that some will say sill ole f**t but it's the C&G ball game and they want you to use the right terminology and if you don't you get marked down.


You are spot on there Malcolm
[video=youtube;l5Mmz1OnCR8]http://www.youtube.com/watch?v=l5Mmz1OnCR8[/video]

 

[Paul.M]

B6 7bu that is brill. Made me chuckle. I've had customers just like that but without the pink hair. The terminology that I messed up on was abbreviation so I would have lost marks stupidly, point taken its just hard for me to remember the correct c&g terminology. As one sparky said to me "wright down how you tie your shoe laces, but you have to do it in c&g language". Something you do every day but I bet you'll loose marks due to terminology.

 

[B6 7BU]

B6 7bu that is brill. Made me chuckle.
but I bet you'll loose marks due to terminology.

Use of correct terminology​

[FONT=CongressSans,CongressSans][FONT=CongressSans,CongressSans]Correct terminology must be used when answering questions.
Candidates continue to use incorrect terminology.
[/FONT][/FONT]