tonights 2391 exam....(10th march 2011)

[lynj]

one thing to say and that is did c&g forget how to be staightforward? felt like some of the questions were half thought......

anyone else take it?

 

[Paul.M]

it dose not matter about the wording for the questions ???
you know if they want you to list the FREEKING R.C.D times !
im just trying to jog peoples memorys, and work out if iv passed.

Bedford I wasn't being condescending in any way, shape or form and I think what you have done above is great. Thank you for taking the time and effort putting it together. The wording of this paper was particular difficult to say the least and by the looks of things a lot of good sparks that know what their doing in the field got caught out in the class room.

 

[chrissimm]

That would depend on whether it was a BS number (200ms) or BSEN (300ms). I haven't seen the paper so don't know.

If my memory serves me well it was a BSEN 61008 but don't quote me on that. Possibly somebody else who done the exam can remember.

Cheers Chris

 

[BEDFORD ELECTIC]

Pm me for past pappers, and stuff ?
IF YOU CAN REMEMBER A 2391 MARCH 2011 MARINER QUESTION POST IT !

when conducting a insulation resistance test on the lamp post curcit, test between live conductors together and c.p.c.
its not practical to remove the contole gear
the photocell on top of the lamp-post must be coverd up to enable the onward wiring of the curcit to be included in the test.
( THE PHOTO CELL---- ACTS AS A LIGHT SWITCH----- all ways include the strapper wires ect ect )
500v dc


Q) discribe how you would conduct a insulation resistance test on a curcit that has SURGE PROTECTION ?

A) test at 500v dc as normal
(BS7671 443.2) surge protection is basicly a bolt of lightning hitting part of the installation.

Q) name 3 locations witch have zones

A) location containig a bath or shower / sauna / swimming pool / water fountain

Q) how do you test the rcd (8 marks)

A) 50% --- 15ma---no trip
100%---30ma--- within 200ms
500%---150ma within 40ms

Q) when the new circit is connected, what will happen to the insulation resistance value, for the whole installation ?

A) the value will decreass

Q) why can you not do Zs-Ze to get the value for R1+R2

A) Ze may containe parralel paths

Q) why dose BS7671 state the mariner cannot be a T.N.C.S system

A) the dangers of water and electric / lower body resestiverty / contact of the body with earth potential.

Q) visual inspection in the shower block c.c.u, list 4 thing to look for (4 marks)

A) external influances
basic protection
correctly selected and erected
any visibal damage
Q) what in the above are you looking for (4 marks)

A) is there warter / dust ???
can some one touch live parts ???
in acordance with BS7671 ???
damage / ware and tear


Q) name 2 bits of infomation, that can only be obtaind via the supply authority.

A) ????? ????????? ????????? ???????? ????????????? ?????????????? ??????????

Q)name the 2 people who can decide the time for a periodic Inspection Report.

A) the designer / the tester

Q) work out the values for R1+R2 (3 marks)

A)0.96+127
-------- = 188
4
Q) name 3 things that may afect the next PIR date (3marks)

A) external influances
type of installation
maintenace shedual
Q) what is the maximum voltage drop for...
lighting ?
power ?
motor ?
A)3 %
3 %
3 % ( see page 358 in Bs7671)
............................Pm me for past pappers, and stuff ?...............................................

 

[IQ Electrical]

You disconnect a surge protective device or you conduct the IR test at 250V DC but with 1 MOhm still used as a minimum value BS7671:2008 page 158.

The disconnection time on a BS EN 61008/9 RCD at 1X I delta n is 300ms. I would bet large sums that C & G would not use a 'BS' residual current device in this exam.

I can't comment on the rest without the paper as there are too many variations on the important parts of the questions.

 

[BEDFORD ELECTIC]

Pm me for past pappers, and stuff ?
IF YOU CAN REMEMBER A 2391 MARCH 2011 MARINER QUESTION POST IT !

when conducting a insulation resistance test on the lamp post curcit, test between live conductors together and c.p.c.
its not practical to remove the contole gear
the photocell on top of the lamp-post must be coverd up to enable the onward wiring of the curcit to be included in the test.
( THE PHOTO CELL---- ACTS AS A LIGHT SWITCH----- all ways include the strapper wires ect ect )
500v dc


Q) discribe how you would conduct a insulation resistance test on a curcit that has SURGE PROTECTION ?

A) test at 500v dc as normal
(BS7671 443.2) surge protection is basicly a bolt of lightning hitting part of the installation.

Q) name 3 locations witch have zones

A) location containig a bath or shower / sauna / swimming pool / water fountain

Q) how do you test the rcd (8 marks)

A) 50% --- 15ma---no trip
100%---30ma--- within 200ms
500%---150ma within 40ms

Q) when the new circit is connected, what will happen to the insulation resistance value, for the whole installation ?

A) the value will decreass

Q) why can you not do Zs-Ze to get the value for R1+R2

A) Ze may containe parralel paths

Q) why dose BS7671 state the mariner cannot be a T.N.C.S system

A) the dangers of water and electric / lower body resestiverty / contact of the body with earth potential.

Q) visual inspection in the shower block c.c.u, list 4 thing to look for (4 marks)

A) external influances
basic protection
correctly selected and erected
any visibal damage
Q) what in the above are you looking for (4 marks)

A) is there warter / dust ???
can some one touch live parts ???
in acordance with BS7671 ???
damage / ware and tear


Q) name 2 bits of infomation, that can only be obtaind via the supply authority.

A) ????? ????????? ????????? ???????? ????????????? ?????????????? ??????????

Q)name the 2 people who can decide the time for a periodic Inspection Report.

A) the designer / the tester

Q) work out the values for R1+R2 (3 marks)

A)0.96+127
-------- = 188
4
Q) name 3 things that may afect the next PIR date (3marks)

A) external influances
type of installation
maintenace shedual
Q) what is the maximum voltage drop for...
lighting ?
power ?
motor ?
A)3 %
3 %
3 % ( see page 358 in Bs7671)
............................Pm me for past pappers, and stuff ?...............................................

 

[IQ Electrical]

'Bedford Electic' why are you multi posting the same stuff over and over?

 

[Jurasic Spark]

'Bedford Electic' why are you multi posting the same stuff over and over?

Yes I was thinking the same.
And his still getting the same ones wrong!!!

 

[paulanderson22]

Q) discribe how you would conduct a insulation resistance test on a curcit that has SURGE PROTECTION ?

A) test at 500v dc as normal
(BS7671 443.2) surge protection is basicly a bolt of lightning hitting part of the installation.

????
I answered 250v d.c. surge protection, lower the test voltage but minimum value should still be 1 meg ohm.

selv and pelv 250v 0.5
upto 600v ac (i think!) 500v dc 1 meg ohm
over 600v ac 1000v dc 2 meg ohm

if i remember correctly!!

 

[Zorro]

R<50 V/Ia

 

[Steve_Wilson]

I don't remember that question coming up but if it did, I would have put down that link the live conductors and test between them and cpc at 500 v DC. No danger of damaging the unit that way. Everybody recently has said about the 30mA rcd, are we now fairly confident that the answer to Q26 was 30mA or are we still stabbing in the dark? I still maintain Shakespeare would have had trouble understanding the comprehension and grammer used in this exam. Please note, I never understood him either

Q) discribe how you would conduct a insulation resistance test on a curcit that has SURGE PROTECTION ?

A) test at 500v dc as normal
(BS7671 443.2) surge protection is basicly a bolt of lightning hitting part of the installation.

????
I answered 250v d.c. surge protection, lower the test voltage but minimum value should still be 1 meg ohm.

selv and pelv 250v 0.5
upto 600v ac (i think!) 500v dc 1 meg ohm
over 600v ac 1000v dc 2 meg ohm

if i remember correctly!!

 

[paulanderson22]

im sure that was one of section a questions.
for the lighting install the scenario stated there was a service cut out in the base of the fitting.
i answered that i would operate all service cut outs and perform ln le ne and all conductors to steel armour.
tricky because i would assume either test method should pick up marks, both testing methods ensure no damage to equipment

 

[Liamsparks]

I think its one for the examiners to discuss between them selfs when they go for their "markers meeting" this week.

 

[jimmy_one_ball]

For the two bits of info only obtainable by enquiry to the DNO (or whatever it was) I answered Frequency and nominal voltage reasoning that everything else you can either see or measure yourself. Alright you can measure the voltage but the nominal is dictated by them at 230.

I read Q26 as additional protection, did they use the word additional? I thought they did, can't really remember now, anyway I said 30mA and the test procedure was for 8 marks suggesting to me they wanted the 5 X IAn as well.

Also can anyone remember the very last part of Q26 , the TT installation has a max dissconection time of 0.2s, how is this affected by the RCD tripping time (of 300ms)!!! I said replace the RCD with a BS type with time of 200ms (0.2s) I realise this is now pants as 0.2 TT time is for overcurrent not additional protection so the answer would be no effect i think.

I also went for the L+N to cpc IR test at 250V dc

Still think I've flunked it. The electrode test, I went for the ELFI tester and did one test for each of the 3 phases and said to use the highest reading, not the mean average of the three like you would with the Electrode potential test. I've never heart of a polyphase TT so I just guessed that's what you might do!

Anyway GL all, see you back here after the re-sit lolZ ATB

 

[jimmy_one_ball]

Oh and do you think they will accept Electricity Supply, Continuity and Quality Regulations? I got Quality and Continuity the wrong way round :0(

 

[IQ Electrical]

There's no requirement to measure Ra with each line.

 

[Gra]

The scenario:

A small marina forming a 400v/230v tt installation with a 100ohm resistance earth electrode, is to be inspected and tested to gain insurance. The installation was completed ten years ago and consists of a seperate shower and toilet block, shop and office and 10x mooring points.

There is no paperwork or certificates covering the exisiting installation.
At the same time a new installation is to take place for three new column mounted lights along the footpath. The lights will be fed from the origin and overcurrent protection by a 608098 16a mcb and fault protection by a bsen61008 rcd. The lights are supplied by swa with a fused cut-out in the base of each column. All control gear for the lights are in the head and an integrated photocell.


The confusing questions:

q.21 a) list the documentation for all electrical installation and state what each covers.

q.23) An insulation resistance test is to be carried out on the SWA cable supplying the new columns. describe the process. Answer should include circuit preparation, instrument to be used and scale, expected result.

q.24) Draw a diagram showing the complete earth fault path of the radial socket in the office.
q.25) It has been agreed that the installation can be isolated for a short period to test the earth electrode. Describe in detail the process.
q.26) a) this was worth two marks? Determine the current rating of the rcd protecting the new column lights.

The provided scenario was the only information given, there were no charts or diagrams presented. The scenario is the wording exact.

I got thrownn by it like everyone.
q.21) straightforward except for the number of dbs on the install? not clear at all
q.23) there will be loads of answers, i went for pull the fuses on the cut-outs, disconnect the neutral on the last and test combine l/n - cpc at 500vdc. I think now it should have been at 250vdc individual tests.
q.24 fine except how many dbs??
q.25 would a direct test with an efli tester been acceptable. did people state record the highest reading or the mean??
q.26) Most seemed to work out the 50/100 for a 500ma rcd. They were put off by this value and went 30ma because special location. Very true except that only applies to a socket outlet so very interested on peoples opinions of that!!

Lets here what your thoughts are, i feel ive missed too many sillly factors when i done thhe exam but it was a bugger for wording!

 

[IQ Electrical]

Ok, documentation, you have to assume that there is 1 distribution board so you will have the PIR, SOTR and SOI, then the EIC, SOTR and SOI.

The IR test is stated to be on the SWA so you could disconnect neutrals at the cutouts with cutout fuses removed and test as normal-this is a new installation. Why would you use 250V?

The installation is existing and has a live supply so the EFLI tester is the instrument of choice for the electrode test, there being no requirement to measure Ra using each line.

I agree with the 500mA rcd requirement, why do you need additional protection on a lamp column? All you need is fault disconnection times to be met.

 

[tony mc]

I take it this that some of the questions are missing as surge protectors and RCD testing have been mentioned alot on the post?

Anyway thanks for the post Gra .

 

[IQ Electrical]

I think the additional protection of 'supplies to pleasurecraft or houseboats' is what confused those that jumped to the 30mA conclusion.

 

[Paul.M]

I'm sure in the scenario it said that one of the swa cores were uses to provide earth and it is the same size as line conductor.

 

[Gra]

very true sorry paul yes the cpc was an integral core and the same size as the line/neutrals.

Tony there were other questions but the ones i highlighted seeme to be the moost controverisal ones and i thought at least if the original scenario was posted then its something to refer back to.

Please ndont take me for gospel because as i say i was thrown with the exam too and although happy with the first half, the second 6 left me feeling ready for june and a resit!

Quick question for those in the know. For the detailed answer questions worth multiple marks, do you lose all the marks if you get one piece wrong or are you given marks for every correct point made? For instance i.r test if you correctly stated the sequence, circuit prep and then got the voltage wrong, would you lose all marks??

 

[IQ Electrical]

very true sorry paul yes the cpc was an integral core and the same size as the line/neutrals.

Tony there were other questions but the ones i highlighted seeme to be the moost controverisal ones and i thought at least if the original scenario was posted then its something to refer back to.

Please ndont take me for gospel because as i say i was thrown with the exam too and although happy with the first half, the second 6 left me feeling ready for june and a resit!

Quick question for those in the know. For the detailed answer questions worth multiple marks, do you lose all the marks if you get one piece wrong or are you given marks for every correct point made? For instance i.r test if you correctly stated the sequence, circuit prep and then got the voltage wrong, would you lose all marks??

There's something about this in either the Exam Success book or the Examiners Report along the lines that candidates will be 'heavily penalised' and when you think about it, it's right-you do all your prep etc. then get the result totally incorrect by not nulling leads on a continuity test or removing parallel paths on external earth loop impedance.

 

[Paul.M]

You would be deducted marks. It works like this:-

Q. For 4 marks. Give me 4 numbers less than ten?

A.2,5,7,12.

You would get 3 out of 4 marks not just 2. Saying that if you put down more than 4 answers they will only take the first four even if the ones after are correct.

 

[IQ Electrical]

I don't think that was what he meant Paul, if you read it again, it's like the example I gave, if you describe the full procedure for continuity of protective conductors but omit the nulling of the leads, the whole test is worthless so marks are decimated.

 

[Paul.M]

That's why I used the example of the first 3 answers are correct, last one wrong so he gets 3 marks and not 2. If on a test sequence and the first step is wrong I agree with you. This was told to me by my instructor, but he wasn't that good. I won't slag him off on here but let's say he's always right, C&G, the regs. College and everyone under the sun is wrong.

 

[benjo]

A 30mA RCD is required for all circuits in TT installations and in special locations.....a Marina is a special location due to the water involved. The scenario deliberately mislead people with the info in the text so some people calculated 500mA. This is irrelevant in a TT system. The question ask you to determine not calculate the RCD tripping current.

 

[IQ Electrical]

A 30mA RCD is required for all circuits in TT installations and in special locations.....a Marina is a special location due to the water involved. The scenario deliberately mislead people with the info in the text so some people calculated 500mA. This is irrelevant in a TT system. The question ask you to determine not calculate the RCD tripping current.

Can you post me the exact quote from BS7671:2008 that makes these requirements?

I must have some missing pages.

 

[IQ Electrical]

Start with Regulation 709.1

 

[IQ Electrical]

Then head over to 411.5.3

Then read it all again and again and again.

 

[Paul.M]

IQ talking to himself again .

BTW the scenario was to install an underground swa using one of the cores as earth to 3 poles for lighting. A switch (can't remember what type) was at the base of the pole and from the switch to the light by flex.

At no time was it mentioned about power to jetty, boats or boat houses. Proximity to water was never declared.

Next time I do a C&G exam I'm going to take a cheeky photo of the paper.