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ta-electrical

Hi, a few exam questions needing answers. Any help would be very appretiated.

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

16)
a) State the test instrument used to measure the earth electrode resistance for...
(i) a generator.
(ii) an instrument protected by an RCD and forming part of a IT system.
b) State the number of readings to be taken for the test in a(i) above.

22) One part of the building has an area where chemical etching and washiing down takes place
(a) (i) List three factors which must be considered when inspecting the containment system in this particular area.
(a) (ii) Identify, for each of the factors given in a(i) above, the human senses that would best determine compliance.
(b) The owner has agreed that the whole installation may be isolated in order for testing to be carried out. There has been a period of one hour allocated for this work. List the tests that must be carried out during this period (individual circuits may be isolated after this period).


26) During the course of the inspection one of the single phase radial circuits supplying an item of fixed equipment is to be checked for voltage drop compliance. The cicuit has the following charactistics;
  • Load current = 45 A
  • Circuit length = 80 m
  • Live conductors = 10 mm2
(a) Using the information in Figure 1 determine whether the circuit meets the requirements for the voltage drop. Show all calculations.
(b) (i) State a suitable observation to be recorded on this oeriodic report if the voltage drops fails to comply.
(ii) State one action which could be taken to rectify the situation in (b)(i) above.

Thanks in advance.
 
11) A circuit which includes surge protection devices is to be tested to determine insulation resistance. State,
a) two methods recognised in BS7671 for safety testing this circuit.
i) disconnect the protective device and measure between lives (inc neutral)and then between lives and earth
ii) reduce the voltage of the test to 250vd.c
b) the minimum test voltage which can be applied.
b 250v d.c

16)
a) State the test instrument used to measure the earth electrode resistance for...
(i) a generator.
external earth fault lop impedence tester
(ii) an instrument protected by an RCD and forming part of a IT system.
earth fault loop impedence tester
b) State the number of readings to be taken for the test in a(i) above.
3 readings

22) One part of the building has an area where chemical etching and washiing down takes place
(a) (i) List three factors which must be considered when inspecting the containment system in this particular area.
i) Corrosion
ii ) wear and tear
iii) the environmental conditions its subjected to Not sure with this could be external influences

(a) (ii) Identify, for each of the factors given in a(i) above, the human senses that would best determine compliance.
i put sight ,sight ,sight lol
(b) The owner has agreed that the whole installation may be isolated in order for testing to be carried out. There has been a period of one hour allocated for this work. List the tests that must be carried out during this period (individual circuits may be isolated after this period).
I put
i) continuity of circuit protective conductors inc main and supplementary bonding conductors
ii Insulation resistance
iii) polarity
iv) external earth fault loop impedence Ze
v) prospective fault current
vi earth fault loop impedence
the ring can be isolated individually not sure if i got this right though mate


26) During the course of the inspection one of the single phase radial circuits supplying an item of fixed equipment is to be checked for voltage drop compliance. The cicuit has the following charactistics;
  • Load current = 45 A
  • Circuit length = 80 m
  • Live conductors = 10 mm2
(a) Using the information in Figure 1 determine whether the circuit meets the requirements for the voltage drop. Show all calculations.
this had me then i did
R = m/ohm/m x length divide 1000
R = 1.83 x 2 x 80 divide 1000
R = 292.8 divide 1000
R = 0.2928
round up to 0.3
vd = R x Ib
= 0.3 x 45
= 13.5v
i wasnt sure as i only had done before by mv x ib x l divide 1000
some say you have to use a correction factor for the increase in temp due to conductor operating temp of 1.2 but i dont know if this is correct because q says use fig 1 and there is no table for correction factors
which when calculated
m/ohm/m at 20c increase for operating temp 70 c difference 50c = 1.83 x 1.2 =2.196
R = 2.196 x 2 x 80 divide 1000
R = 351.56 divide 1000
R = 0.35136
vd = R x ib
= 0.35136 x 45
= 15.8112
rounded down 15.8v
to calc by mv x Ib x length divide 1000
2.2 x 2 x 45 x 80 divide 1000
= 15840 divide 1000
= 15.84v or 15.8v rounded down




(b) (i) State a suitable observation to be recorded on this periodic report if the voltage drops fails to comply.
observation voltage drop of 13.5v exceeds maximum of 5% 11.5v max
(ii) State one action which could be taken to rectify the situation in (b)(i) above.
increse CSA of conductors

dont take this as gospel as i may be wrong but i passed so i got enough right lol
 
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11)b) The owner has agreed that the whole installation may be isolated in order for testing to be carried out. There has been a period of one hour allocated for this work. List the tests that must be carried out during this period (individual circuits may be isolated after this period).
I put
i) continuity of circuit protective conductors inc main and supplementary bonding conductors
ii Insulation resistance
iii) polarity
iv) external earth fault loop impedence Ze
v) prospective fault current
vi earth fault loop impedence
Would suspect that quite a few of these could be done by isolating individual circuits and earh fault loop impedance can only be done when the circuit concerned is energised.

Not certain myself by any means but would think it is more like Ze - because earthing conductor has to be disconnected to do this so rest of installation would be unsafe if left energised. Equally continuity of earthing conductor and main protective bonding conductors. To measure these one end would have to be disconnected to to remove parallel paths and in doing so the installation would again be potentially dangerous so would have to be de-energised.
I wouldn't include PFC, as for this the earthing conductor and parallel paths from main protective bonding are all in place.
Not wanting to be picky , just trying to find the right answers:)
 
I know what you mean mate no i was trying to go from memory of what i had put but i dont know if i did put zs as you say its a live test
i continuity of cpc and bonding
ii ir
iii polarity by continuity methods?
iv polarity live at supply
v Ze
vi pfc

would you say that sounds better
and the continuity of ring carried out by isolating seperatley
i cant remember what i put

there has to be six as there are six marks
pfc has to be done with supply live but the installation de energised
asdoes ze
continuity would have to be carried out on the bonding and ir on all
as for continuity of cpc then as you say you could carry out seperatley but this has to be done before a ir so i think you would have to do it as you only have 1 hour
and you cant just go straight to a ir test as this will not show if the cpcs are continous only

as i say dont take it as gospel as i passed but they dont tell you what you got wrong
 
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Yeah who knows what is in the mind of the examiners :confused:
6 marks and nothing for reasons? yep it does just say "list" !

I would still say that there is no reason why pfc can't be done with the installation live as you want the highest value so you want all the parallel paths from main bonding to be in place. On the other hand you do Ze, reconnect the earth and it's 30secs more to do pfc. Will have another read of gn3 later and see if there are any clues.
 
Hi pushrod
yes they have there own language and when they say list its in order of the test sequence if for initial verification
but for pir it can be done in ay order
when doing Ze and pfc at the origin, the Supply is live on the supply side of main isolator switch but the installation should be de- energised by switching off the main switch and all rcds and breakers
the earthing conductor is disconnected to remove parallel paths for Ze so you get the true value

for pfc the main earthing is in place and so is the bonding as this is how it will be if a fault develops and will allow the maximum current to flow to break the protective device in the required operating time or faster because the lower the resistance the more current will flow which is what we want to achieve
 
Question 16a is an earth electrode resistance tester, you must have typed on autupilot Brucelee because you've got the correct number of readings to be taken! :)
 
sorry iq
you are correct i have mistakenly put external earth fault loop impedence tester
earth electrode resistance tester Is the correct answer as you say
that wiil teach me for not concentrating on what i was doing lol
cheers for pointing out my mistake the answer is i the question hehe doh!
 
The volt-drop question was rather ill thought out, we were convinced it would be pulled from the exam but the examiners report states that the question was still used!

The big debate was around the 1.2 temperature factor-the rest of the question had every right to be there as volt drop is part of the inspecting/testing process.

We thought that the 'observation' to be recorded at the end of the question was actually referring to the defect code to be allocated-another silly question as it could have been 2,3 or 4 depending on whether the volt drop had any safety implications on the item of fixed equipment-BS7671 actually says that the 3/5% levels can be exceeded where there is no danger.
 
i had only ever been shown mv x ib xlength divide 1000 and this is what i was thinking weres the mv table or value?
but after reading a few times i started to realise to work it out from the resistance using ohms law
I saw that the 1.83 value was for conductors at 20c
and had been practicing other questions with correction factors
and as i wasnt sure what they were asking for with regard to observation i think i put voltage drop excessive and exceeds the maximum 5% rule of 11.5v and i may have put code 2
hard to know now as you dont see the paper again or getting any feedback on the areas you did well and the areas you failed to answer correctly
they would be better sending you a copy back of what you got right or wrong to the centre were you took the exam so students could get feedback and revise accordingly for the future
so beacuse there was no table for correction factors i did it without a correction factor for increase conductor temp due to load current and as it was two conductors i should have known to add this to to calculation but the exam makes you nervous and the way they word the questions
 
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