2394 past paper scenario need help please anyone.

[N6rul]

Scenario
The building has its own supply and forms part of a 230 v TT System. Ze and PFC have not been measured. All circuits are wired in 70 degree Celsius thermoplastic single core cables, with copper conductors, in surface mounted, galvanized steel trunking and conduit. All accessories, including the distribution board, are metal clad. All circuits are protected by type B circuit breakers to BS EN 60898 Apart from the socket outlet circuit and the lighting circuit which are protected by individual RCBOs to BS EN 61009-1. the main switch is a double pole 100 A, 300 A S-type RCD to BS EN 61008-1.
PLEASE SEE ATTACHMENT FOR DIAGRAMS.

QUESTION 1
The ring final circuit is to be tested prior to connection to distribution board.
A) explain in detail how the continuity of ring circuit conductors test would be carried out.

B) determine the expected results for each stage.

C) a test of external loop impedance is to be carried out to assess the effectiveness of the earth electrode. Describe how this test is to be carried out after safe isolation of the installation has been complet.

Please can someone help. Thanks

 

[Jurasic Spark]

Theres no point anyone typing out a reply when all you have to do is look in GN3 or the O.S.G where there is a clear and concise explantion

 

[brucelee]

Hi mate have you got GN3 as its all in there also the OSG and regs part 6 and 7 helps with 2394 as regards zones and rcds etc for special locations or installations

read GS38
memorandum of guidance on elecy at work regs
chris kitchers guide to I&T
there are others such as scaddons books

all these books will help your course material and tutor should help you out ad show you how to answer also
but mainly its down to you mate


are you asking how to explain how to carry out a continuity of ring final circuit conductors is so
the exam success book will help you with this as it has 2 full exam papers with questions and answers exactly as C&G want the questions answered its all about correct terminology
is the installation existing or a new installation
this answer may be worth 15 marks for a full description of a test procedure

best way is to use bullet points
If its a existing the you will also have to include safe isolation
using a low resistance ohmeter and not a continuity tester and include checking meter and leads that its functioning correctly state the scale Ie low ohms
its a 3 step test
step 1 end to end resistances of line, neutral and cpc loop values
step 2 cross connection of outgoing line to incoming neutral and vice versa for remaining L and N test at this connection and alll accessories readings should be substantially the same ie within 0.05ohms of each other any readings higher than this could indicate a spur
step 3 cross connection of Line and CPC carries out as per step 2 again readings should be substantially the same at the join and all accessories
higher readings could indicate spurs or loose connections
the highest reading is the R1 + R2 value and should be recordd on the schedule of inspections
in bullet points something like
if existing install then something like below if New install ie initial verification then no need to include the safe is and proving dead as this will be prior to connection and before energising

seek permission to isolate supply, Erect barriers and warning notices warn people in vicinity
Locate and identify the supply, lock off, Label, CBs off,
select a GS38 approved voltage indicator prove working on known supply or suitable provig unit
Prove dead between L-N, L-E and N-E for single phase
L1-L2, L1-L3, L2-L3, L1-E,L2-E, L3-E, L1-N, L2-N,L3-N and N-E for 3 phase 4 wire supply
re prove voltage indicator to prove working at time of test
Identify the Line, Neutral and cpc and measure seperatly
Select a low resistance ohmeter confirm calibration no damge and functioning correctly
Set to low ohms note resistance of leads or auto null
Step1 end to end
Connect 1 lead of tester to outgoing line and the remaining lead to the incoming line
carry out test, note value this is r1
repeat procedure for N and cpc these are r1 and rn and r2 respectively
the values obtained should be substantially the same ie within o.05ohms of each other if same size conductors used
if cpc has smaller csa then the cpc loop values will be higher approx 2.5mm/1.5mm= 1.67 times higher than Lor N values

step 2
cross connect Line and Neutral at Db
check to confirm that outgoing line is connected to incoming Neutral and vice versa ( as per diagrams On site Guide and GN3)
mesure resistance values at this join and each socket outlet or accessory
the readings should be substantially the same Ie agin within 0.05 ohms of each other
the value should be approx one quarter the resistance of the Line plus Neutral loop values from step 1 Ie r1+rn / 4 = (R1+RN)
the highest reading is the R1+RN value for the circuit
any sockets wired as spurs will give higher value

Step 3
cross connect as per step 2 above

check to confirm cross connected correctly
repeat procedure as step 2 above but wit line and CPC cross connected
again measure resistance at this join and all socket otlets and accessories
the readings will be substantially the same within 0.05ohms of each other and will be approx one quarter the resistance of the Line + CPC loop values from step 1 ie
r1+r2/4 = R1+R2
again spurs will give higher values
the highest reading is the R!=R2 for the circuit ad should be recorcded on the schedule of test results in the appropriate column
disconnect instrument, reconnect conductors , reinstate supply and confirm functioning correctly

basically mate something like above but include as much as you can but write it out a few times and alter but try to keep all relevent info such as low resistance ohmeter , calibration , set to low ohms etc etc

If you search the forum for 2391 and testing procedures there is loads of threads and psots on this
Buy the exam success and deffo GN3

the second is worked out from resistances of the coductors by using
m/ohm/m x Length of the circuit
step 1
Ie r1 = m/ohm/m x Length /1000
= 7.41 x 27m /1000
= 0.20007 round down
= 0.20 ohms
repeat for r2 but the cpc is smaller m/ohm/m is 12.1 x 27/1000 = 0.3267 round up 0.33ohms
rn is same size as r1 so will be the same but still show the calculation
step 2 cross connect Line and Neutral
R1+RN = r1+rn /4
= 0.20+ 0.20/4
= 0.40/ 4
= 0.10
step 3
R1+R2= r1+r2 / 4
= 0.20 + 0.33/4
= 0.1325 round down
= 0.13 ohms
this is the value you should expect to find at the cross connection and all socket outlets and accessories

good luck mate
I will leave Q 3 to someone else but i strogly advise you get the exam success book as it has example answers for all tests

some of these you can include diagrams and sometimes they ask for brief description with calculation or with diagrams

hope its some help get reading GN3 , OSG regs and all other books practice calculations etc and diagrams especially for earth fault loop etc

I did the 2391-10 which is basically 2394 and 95 in 1 course
I revised every day upto 12 hrs a day for 4 months and then did the course which was a 8 week 3hrs each week and then the exam and I studied as much as i could while on the course 4 out of 10 passed I was the only one not working in the industry the others either didnt have time or couldnt be bothered really to put the effort in

its all about how much you put in and want to learn a lot harder than all other quals

so again I wish you luck

 

[N6rul]

thanks mate

I'm in the same boat as you, but as you are aware these training facilities just want to take your money. I had to pay out of my own pocket. I was not concerned paying for the course but what hurts is they don't give a damm. I have my exam next month and looking at the past paper, we were not shown or taught half the stuff. I'm really trying studying 10 hours a day, but sometimes it's difficult when you dint have practical experience to read and get it imbedded in your head. But it was very nice of you to take time out to help. Thanks
Can I just ask if a location has galvanised conduit, would I need to do a continuity test on the conduit, or link to galvanised metal.
What has also confused me is the socket ring is on a s-type breaker, does that make a difference for insulation resistance test or PFC. I'm sure I read some where the aux needs to be taken off on a RCBO, but for which part of the test I cannot remember.

 

[SirKit Breaker]

To answer question C would be a long winded job with my typing speed. The full explanation goes in depth, but as this may crop up in your exam, then you need to know it from memory. You not only need to know the test procedure, but you also need to know what instrument to use, and there is a choice of 3, you need to know all 3, and you also need to know the specification of these instruments. So i am going to back up Jurrasic Spark on this one, you need to get GN3, and you need to do a lot of reading. If i or anyone else wrote the script, it may not have the same depth of detail that GN3 contains. You wont have a cat in hells chance of passing the exam if you don't have a detailed and in depth knowledge of this book.

Cheers..........Howard

 

[growler]

im doing my 2394 and the teacher hasnt got any past papers to give us. im screwed basically !

 

[Guest154]

brucelee is spot on apart from his calculations the cable is thermoplastic so the calculations should have a factor of 1.2 in them so it will be
7.41 times 27 times 1.2 divided by 1000 , this is one of the things they try to catch u out with in the tests , just incase anyone is using this for their test

 

[Jurasic Spark]

brucelee is spot on apart from his calculations the cable is thermoplastic so the calculations should have a factor of 1.2 in them so it will be
7.41 times 27 times 1.2 divided by 1000 , this is one of the things they try to catch u out with in the tests , just incase anyone is using this for their test

1.2 is the muyltiplying factor to convert a resistance reading from 20 degrees to 70 degrees C.
So why do you reckon you have to do this to answer this question????

 

[Guest154]

its also the factor for thermoplastic cable

 

[Guest154]

thats y in the question they mention it , to catch u out

 

[LittleHelper]

im doing my 2394 and the teacher hasnt got any past papers to give us. im screwed basically !

Try these past papers City & Guilds 2391 Revision Questions 2391 sample questions

 

[Jurasic Spark]

its also the factor for thermoplastic cable

The question gives milli ohms/m at 20 degrees C and askes what your expected readings would be. Why do you think you need to multiply by 1.2. I'm sorry but I think you've misunderstood something. 1.2 is the multiplying factor to go from 20 degrees to 70 degrees resistance readings.

 

[Guest154]

if u check the OSG there is also a factor for thermoplastic cable , also in GN3 am not tryin to be smart just giving poeple a heads up as its comon to fail because of this

 

[NickD]

Re: thanks mate

I'm sure I read some where the aux needs to be taken off on a RCBO, but for which part of the test I cannot remember.

Insulation resistance test. RCBO can be damaged by 500V if you don't off the auxiliary earth.

 

[NickD]

if u check the OSG there is also a factor for thermoplastic cable , also in GN3 am not tryin to be smart just giving poeple a heads up as its comon to fail because of this

What factor's that then mate? For multiplying by what to achieve what? Just saying "it's for thermoplastic cable" is a bit vague. Not being funny, genuine question as I'm bemused.