2391 Odds and sods

[La Poste]

Greetings all.

I hope it's Ok to throw a few odds and ends that I am not sure about in this thread to see what people think.

1. When IR testing SWA cable and the Armour is not used as the CPC but is earthed is it correct to disconnect the earthing to the armour before doing the test.
Also when doing an R1+R2 test on SWA cable is it necessary to remove the earthing of the armour?
The R1+R2 test is done by connecting line and earth at the board feeding the circuit

2. When IR testing an individual circuit at a DB that is part of a TN-C-S system
We would isolate the individual circuit leaving the rest of the installation energised. After ensuring safe isolation and before beginning our IR test we would need to remove the neutral of the individual circuit from the board as the main switch is still closed. Is this correct?

3. To avoid confusion on the earth fault loop impedance and Ze test would it be appropriate to just say for Ze we test between line and earth, line being at the supply side of the main switch and then for the Zs test on a lighting circuit to test between switched line and earth at the furthest part of the circuit.
What I mean is don't even bothering mentioning to connect the neutral, just say my tester is a two lead tester.

4. Going back to surge protectors on sockets which I am still not sure about.
When IR testing the circuit with surge protectors do we
test between line, neutral and earth separately at 250V DC or do we link line and neutral together and test between them and earth at 250V DC?

Any thoughts.

Thanks alot.

 

[gap30]

Greetings all.

I hope it's Ok to throw a few odds and ends that I am not sure about in this thread to see what people think.

1. When IR testing SWA cable and the Armour is not used as the CPC but is earthed is it correct to disconnect the earthing to the armour before doing the test.
Also when doing an R1+R2 test on SWA cable is it necessary to remove the earthing of the armour?
The R1+R2 test is done by connecting line and earth at the board feeding the circuit

2. When IR testing an individual circuit at a DB that is part of a TN-C-S system
We would isolate the individual circuit leaving the rest of the installation energised. After ensuring safe isolation and before beginning our IR test we would need to remove the neutral of the individual circuit from the board as the main switch is still closed. Is this correct?

3. To avoid confusion on the earth fault loop impedance and Ze test would it be appropriate to just say for Ze we test between line and earth, line being at the supply side of the main switch and then for the Zs test on a lighting circuit to test between switched line and earth at the furthest part of the circuit.
What I mean is don't even bothering mentioning to connect the neutral, just say my tester is a two lead tester.

4. Going back to surge protectors on sockets which I am still not sure about.
When IR testing the circuit with surge protectors do we
test between line, neutral and earth separately at 250V DC or do we link line and neutral together and test between them and earth at 250V DC?

Any thoughts.

Thanks alot.

can i give my thoughts and people can correct me if i am wrong

1. the earthing of the swa is connected via a 'banjo' via the gland usually at the metalclad db/isolator so no you would not disconnect this - you could in theory disconnect the earthing cable connected to the banjo but i think the gland would still be earthed to the db/isolator

2. yes you would remove all three conductors so the test could be carried out ie l-n,l-e,n-e

3.yes i think its only the flukes that require a neutral for zs/ze but in 2391 land yes i would mention the neutral for zs i think?

4. i think you could test as normal due to the low test current ie 250v dc but dont forget its still 1 megohm minimum resistance value

 

[VMan]

hi La poste, you tried out the June 11 Quiz yet?
I also have 2391 tomorrow, just did the June quiz in an hour and a half, didnt even get to use my crayons! hope so tomorrow!

I have a question regarding sequence of test:

For radial the 1st four sequnces wil be
Continuity of CPC's
Insulation Resistance
Polarity ( dead & Live)
Earth fault loop impedance

For ring main circuit;
(Do i need to do contiunuity of cpc's as 1st step?? don't see why if i'm testing just this circuit)
Continuity of Ring Final Circuits (step 1&3 will confirm continuity of cpc?)
Insulation Resistance
Polarity ( Dead & Live)
Earth fault loop impedance

ok on June 11 paper,
Q8 - State, when testing the continuity of a radial circuit cpc using the line and cpc,the
a)Instrument to be used ( i got this one )
b) action to be taken regarding these conductors, prior to carrying out the test (Link them together?)
c) Significant of the test results obtained at the furthest point of circuit (R1+R2)?? or it should be highest value on the circuit?

well its a little late to worry to much now, i don't know how much more i can learn. the june paper seemed easy but without marking its hard to tell.
Just noiced i missed out switching any two way or intermediate switches when doing IR on lighting circuit - surely they should think about looking at the practical and noticed if you did it as in real life its something that is second nature to do, but when under pressure to write it down within a time limit it may slip my mind but hey thats C&G.

Good luck anyway guys

 

[La Poste]

Thanks for the replies.
I'm with you tomorrow night Vman.
I'll see if I can nab a test paper for the lads on here.


Still not sure about the SWA though, maybe it's best to remove the CPC of the SWA cable from the board altogether and then test to avoid any involvement of the armour in the testing.

 

[VMan]

Thanks for the replies.
I'm with you tomorrow night Vman.
I'll see if I can nab a test paper for the lads on here.


Still not sure about the SWA though, maybe it's best to remove the CPC of the SWA cable from the board altogether and then test to avoid any involvement of the armour in the testing.

Think about it this way.

if you have 3 cores on the SWA as you are suggesting ( because the Armour is not being used as a CPC) then to do your R1+R2 you simply link the CPC core of the SWA to the LINE core of the SWA.

it doesn't matter if the SWA armour is connected to earth or not as its not connected to either the CPC or line (except in earth terminal)

As for Insulation resistance, again it doesn't make any difference as the armour is essentially a 4th core to the cable. so just test between the cpc and line as normal.

if the armour was used as a cpc then its a different story.

make sense? or have i got the question wrong?

where you sitting your 2391 mate?

 

[gap30]

hi La poste, you tried out the June 11 Quiz yet?
I also have 2391 tomorrow, just did the June quiz in an hour and a half, didnt even get to use my crayons! hope so tomorrow!

I have a question regarding sequence of test:

For radial the 1st four sequnces wil be
Continuity of CPC's
Insulation Resistance
Polarity ( dead & Live)
Earth fault loop impedance

For ring main circuit; - RING FINAL CIRCUIT GET THE TERMINOLOGY RIGHT - IQ, WIDDLER, BRUCELEE,,MALCOLM,SPIN,TELETRIX HAVE BEEN BANGING ON TO ME ABOUT THIS FOR WEEKS!!!!!!!!!!
(Do i need to do contiunuity of cpc's as 1st step?? don't see why if i'm testing just this circuit)
Continuity of Ring Final Circuits (step 1&3 will confirm continuity of cpc?)
Insulation Resistance
Polarity ( Dead & Live)
Earth fault loop impedance

ok on June 11 paper,
Q8 - State, when testing the continuity of a radial circuit cpc using the line and cpc,the
a)Instrument to be used ( i got this one )
b) action to be taken regarding these conductors, prior to carrying out the test (Link them together?)
c) Significant of the test results obtained at the furthest point of circuit (R1+R2)?? or it should be highest value on the circuit?

well its a little late to worry to much now, i don't know how much more i can learn. the june paper seemed easy but without marking its hard to tell.
Just noiced i missed out switching any two way or intermediate switches when doing IR on lighting circuit - surely they should - THE EXAMINER WILL NOT SECOND GUESS YOU HAVE TO BE RIGHT FIRST TIME think about looking at the practical and noticed if you did it as in real life its something that is second nature to do, but when under pressure to write it down within a time limit it may slip my mind but hey thats C&G.

Good luck anyway guys

ring final circuit

continuity protective conductors
continuity ring final circuit conductors
insulation resistance
polarity - dead and live

READ THIS

exam success book page 68

a ring final circuit continuity test is to be carried out on a newly installed circuit. State

a. the instrument to be used
b. two additional tests that are automatically carried out when completing this test.

answer
a. low-resistance ohmmeter
b. continuity protective conductors/polarity

comments by examiner

b. stating r1 + r2 would not be an acceptable answer

I AM AN EXPERIENCED SPARK AND I HAVE FAILED THIS EXAM BEFORE - PEOPLE ON THIS FORUM HAVE DRUMMED IT INTO MY HEAD THAT YOU HAVE TO BE 100% IN YOUR ANSWERS - THE NIGHT BEFORE THE EXAM I PLAN TO READ GUIDANCE NOTES 3 FROM COVER TO COVER TO REFRESH ANYTHING IN MY HEAD

GOOD LUCK!!!!

 

[VMan]

I AM AN EXPERIENCED SPARK AND I HAVE FAILED THIS EXAM BEFORE - PEOPLE ON THIS FORUM HAVE DRUMMED IT INTO MY HEAD THAT YOU HAVE TO BE 100% IN YOUR ANSWERS - THE NIGHT BEFORE THE EXAM I PLAN TO READ GUIDANCE NOTES 3 FROM COVER TO COVER TO REFRESH ANYTHING IN MY HEAD

GOOD LUCK!!!!

That will be now then for me?!?! the GN3 book and sequence of each test is not a problem for me to remember , but obviously some has to be common sense, when i take on so much learning things start getting mixed up.

cheers for that i have got the exam success book and will go through paper 1 again now. i haven't even looked at paper 2 yet as i have the day off tomorrow and plan on doing paper 2 in the morning and brushing up on what i didn't get right after.

Some 'paper and answer' papers i have got of tinterweb have wrong terminology in them which messes with my head too. all be over this time tomorrow (i hope).

 

[La Poste]

My test is in Guildford but I have tomorrow all day to revise as well.
As for the SWA I was thinking that an IR test between Line and CPC, you would also have the armour as an additional connection to earth so it would almost be as if you were testing the line against two CPC's if you know what I mean.
The IR would be read between the line and the CPC but also between line and armour because the armour is also connected to earth at the board.
R1 + R2 probably wouldn't make that much difference due to the low voltage of the test instrument but IR is done at 500V so you could theoretically get leakage current from line to CPC and also from line to armour, that is why I asked the question should the armour be disconnected.
Personally I don't think it should but City and Guilds might think different.
I've been reading the electricity at work regulations 1989 and very thrilling they are too.
Still time to do one more test paper before bed though.

 

[gap30]

That will be now then for me?!?! the GN3 book and sequence of each test is not a problem for me to remember , but obviously some has to be common sense, when i take on so much learning things start getting mixed up.

cheers for that i have got the exam success book and will go through paper 1 again now. i haven't even looked at paper 2 yet as i have the day off tomorrow and plan on doing paper 2 in the morning and brushing up on what i didn't get right after.

Some 'paper and answer' papers i have got of tinterweb have wrong terminology in them which messes with my head too. all be over this time tomorrow (i hope).

i have done these several times, these are the only papers on record that a proper city and guilds examiner has shown you the answers and provided tips for you - do them again, and again if you need to

make sure you pass lol!

 

[VMan]

My test is in Guildford but I have tomorrow all day to revise as well.
As for the SWA I was thinking that an IR test between Line and CPC, you would also have the armour as an additional connection to earth so it would almost be as if you were testing the line against two CPC's if you know what I mean.
The IR would be read between the line and the CPC but also between line and armour because the armour is also connected to earth at the board.
R1 + R2 probably wouldn't make that much difference due to the low voltage of the test instrument but IR is done at 500V so you could theoretically get leakage current from line to CPC and also from line to armour, that is why I asked the question should the armour be disconnected.
Personally I don't think it should but City and Guilds might think different.
I've been reading the electricity at work regulations 1989 and very thrilling they are too.
Still time to do one more test paper before bed though.

but think about if you had 2 circuits running together in 1 conduit, and both had there own cpc, do you disconnect the cpc from the MET or do you put the crocodile clip on the MET to do your IR test? effectively the ir is testing between 2 cpc's and line this way too!

 

[VMan]

i have done these several times, these are the only papers on record that a proper city and guilds examiner has shown you the answers and provided tips for you - do them again, and again if you need to

make sure you pass lol!

i plan to, been averaging ( according to papers off he net) about 75% i try to be strict when answering them.

ok im off to do paper 1 again.

 

[gap30]

but think about if you had 2 circuits running together in 1 conduit, and both had there own cpc, do you disconnect the cpc from the MET or do you put the crocodile clip on the MET to do your IR test? effectively the ir is testing between 2 cpc's and line this way too!

no two circuits in one conduit you would test for electrical separation, you would link line and neutral on circuit one and test between line and neutral in circuit two (this is a different scenario)

guidance notes 3 page 41

the live parts of the separated circuits must be tested to ensure that they are electrically separate from other circuits. This is achieved by testing between the live conductors of the separated circuit connectd together and the conductors of nay other adjacent circuit strapped together

 

[Jay Sparks]

When doing the IR test you would leave the swa conected to the MET. Think of a domestic cu, you would normally put one croc clip on the MET and test between the line of each circuit. If there was a low reading on one of the circuits, you then dissconect the cpc, neutral and line for that circuit and test it seperately. Other wise, if all the readings were fine you would then connect the other croc clip to neutral and test between cpc & neutral, then line & neutral.

Jay


p.s Good luck with the exam tomorrow lads.

 

[VMan]

When doing the IR test you would leave the swa conected to the MET. Think of a domestic cu, you would normally put one croc clip on the MET and test between the line of each circuit. If there was a low reading on one of the circuits, you then dissconect the cpc, neutral and line for that circuit and test it seperately. Other wise, if all the readings were fine you would then connect the other croc clip to neutral and test between cpc & neutral, then line & neutral.

Jay


p.s Good luck with the exam tomorrow lads.

thats what i was trying to say!

 

[VMan]

ring final circuit

continuity protective conductors
continuity ring final circuit conductors
insulation resistance
polarity - dead and live

READ THIS

exam success book page 68

a ring final circuit continuity test is to be carried out on a newly installed circuit. State

a. the instrument to be used
b. two additional tests that are automatically carried out when completing this test.

answer
a. low-resistance ohmmeter
b. continuity protective conductors/polarity

comments by examiner

b. stating r1 + r2 would not be an acceptable answer

I AM AN EXPERIENCED SPARK AND I HAVE FAILED THIS EXAM BEFORE - PEOPLE ON THIS FORUM HAVE DRUMMED IT INTO MY HEAD THAT YOU HAVE TO BE 100% IN YOUR ANSWERS - THE NIGHT BEFORE THE EXAM I PLAN TO READ GUIDANCE NOTES 3 FROM COVER TO COVER TO REFRESH ANYTHING IN MY HEAD

GOOD LUCK!!!!

umm... Read page 39 exam success, Q7 :

State, in the correct sequence, the first THREE test to be carried out on a new ring final circuit.

Answer:
- Continuity of protective conductors
- Continuity of ring final circuit conductors
- Insulation resistance

Alternative answer:

- Continuity of ring final conductors
- insulation resistance
- earth fault loop impedance.

it seem if you dont include continuity of protective conductors, you dont include polarity as it has already been confirmed as has continuity of protective conductors!!

 

[gap30]

yes mate i was trying to highlight the r1 + r2 part, i got the shock of my life when i read the examiners comments!

 

[gap30]

good luck

 

[La Poste]

Referring back to SWA again there is no mention of special IR tests but GN3 page 34 states:

"Installation incorporating SWA will introduce parallel paths to protective conductors.
In such situations the R1+R2 test will need to be done prior to final fixing"

So there you go, there is no mention of special IR test procedures but R1+R2 is specifically mentioned so I guess you would have to remove the CPC from the board to test R1+R2 if the SWA had been already installed and the armour had been earthed.
It would be easier doing this way than trying to remove the armour earthing if you had a metal clad board.

 

[Deleted member 26818]

Really only applies when the armour is being used as the CPC, same with metal conduit and trunking.

 

[VMan]

Referring back to SWA again there is no mention of special IR tests but GN3 page 34 states:

"Installation incorporating SWA will introduce parallel paths to protective conductors.
In such situations the R1+R2 test will need to be done prior to final fixing"

So there you go, there is no mention of special IR test procedures but R1+R2 is specifically mentioned so I guess you would have to remove the CPC from the board to test R1+R2 if the SWA had been already installed and the armour had been earthed.
It would be easier doing this way than trying to remove the armour earthing if you had a metal clad board.

did you do another test paper?

it will only introduce parallel paths if used a a cpc, if it has separate cpc then it wont introduce parallel path the the separate cpc.

think if the swa is cpc and its connected to metal conduit via gland, then when u measure the armour as cpc its adding the parallel paths, where if its a 3 core cpc, the cpc is not connected to the metal conduit!

i will try draw a pic

 

[gap30]

Referring back to SWA again there is no mention of special IR tests but GN3 page 34 states:

"Installation incorporating SWA will introduce parallel paths to protective conductors.
In such situations the R1+R2 test will need to be done prior to final fixing"

So there you go, there is no mention of special IR test procedures but R1+R2 is specifically mentioned so I guess you would have to remove the CPC from the board to test R1+R2 if the SWA had been already installed and the armour had been earthed.
It would be easier doing this way than trying to remove the armour earthing if you had a metal clad board.

well done mate i was reading up on that last night as well, gn3 giving reference to testing at various stages of the installation to avoid this exact situation

 

[La Poste]

Maybe a special mention in the answer that the armour is not being used as CPC so need to disconnect it.

I mean in reality the armour is separated from the line conductor within by two sets of insulation, one covering the line cable and one covering the line neutral and cpc.
With all that insulation between the armour and the line I can't see how it would affect the results of an IR test and if it did you would want to know about it.
You would want to know if you had bad insulation between the armour and the line.
So it would be best to leave it earthed in my opinion.
But City and Guilds might see it different.
Do you see what i am getting at though, leakage from line inside cable to armour is kind of a parallel path because the armour is also earthed at the DB same as the CPC

 

[Deleted member 26818]

You wouldn't disconnect if it wasn't being used as a CPC.

 

[VMan]

sorry its small and crap it was rushed, (and colours are wrong)
so the top image uses armour as cpc, you see when you do r1+r2 it will include the bonding to my fabulous pipe and back to the met, a parallel path.

the bottom image you can do the r1+r2 with the cores it will not include the armour just the cpc core and line core

make sense? hopefully there wont be a question on this!

 

[gap30]

i have only ever once tested well insulation on armour and that was a fault on an underground swa in a duct for street lighting - turns out the brown was damaged so i used black and grey for line and neutral (identification of conductors of course) and the armour as earth, made brown safe - lovely thought i was gonna be there all day lol