2391 Inspect and test help and guidance.

scope02 · Nov 4, 2011

Hey,

I haven't posted anything on a forum before, but someone recommended this site to me, so here it goes.. Hope you all can help?!

In two weeks time i am starting my 2391 exam, i don't have much practical experience, but i was wondering what is the best way to approach this exam, both written and practical, as it three phase system and i don't know really where to start in terms of inspecting it or testing the installation. Any suggestions, past papers questions and best systematic way to approach the testing would be of great assistance.

Many Thanks

Scoop02

trev · Nov 4, 2011

Do you mean in 2 weeks you're sitting the exam or starting the course?
If its sitting the exam you need to get stuck in to guidance note 3. If you're starting the course you still need to get into GN3 but you have a bit more time to read,digest and understand it. You'll be taught the test procedures and what results to expect, and theres a shedload of threads on here which will tell you what to expect.
Good luck

ezzzekiel · Nov 4, 2011

guidence note 3, city guilds exam success and a practical guide to inspection and testing will give all the theoretical knowledge if you have no experience (really may b too soon for you to be doing 2391) then training on a mock up board or at home (safely) is all you can do

trev · Nov 4, 2011

ezzzekiel said:
guidence note 3, city guilds exam success and a practical guide to inspection and testing will give all the theoretical knowledge if you have no experience (really may b too soon for you to be doing 2391) then training on a mock up board or at home (safely) is all you can do

I have to agree here, the lecturer on my 2391 said C&G guidlines were A) Qualified spark B) Well versed in regs C) Actively involved in I&T.
There was a taxi driver on the course though.

chelwood · Nov 4, 2011

I managed to get through first time having taken the course over twelve weeks.Personally i think its to much an ask to do it in 4 or 5 days unless you are very experienced at testing.Read the books alreasdy mentioned from cover to cover and back again and good luck

tony mc · Nov 4, 2011

If you search the forum you will find lots of very useful info to get you on the right track.

If you get stuck someone will always be able to help when you ask

.2391 sum practical help

Good luck

johnelectrical · Nov 4, 2011

For the theory exam, go straight to the long questions, raed the scenario, then read it again, highlight things you are likely to have to refer to, Ze earthing system etc. that way you will spend less time looking for things during writing the answers. the reason for doing the long questions first is to reduce the risk of remembering details from the short questions. as an example sapposing question 16 asks for external fault path for a TN-S system but the long question is based on a TT system, 2 hours into the exam you may remember question 16 rather than the scenario. Do all the long questions first, make sure you put the number of the question you are answering in the margin on the left. then do the quicker short questions. remeber to always put your working out, that way you still get some marks even if you make a silly mistake for the answer. as for the practical make sure you do safe isolation properly. make sure the installation is dead when you do continuity of main protective bonding conductors AND Ze. as other people have said read GN3 cover to cover. for this exam it is the Bible. as for the IET/C&G exam success book, generally good except for how to do insulation resistance which must always be tested to EARTH not to cpc (plus L-L)
good luck

scope02 · Nov 4, 2011

Thank you for all your constructed comments, Single phase supplies i can get my head round even with the lack of practical work, but i managed to get a glimps of what the 2391 installation looks like, and that looks a bit tricky, Three phase supply feeding a single phase db, i gather testing continuity of the main earth bonding for the Three phase supply is done in the same way as the single phase db that you test in the 2392?? then move on the remaining circuits for the three phase board.. i.e a fuse spur i think was there, and a circuit for a motor with an under current protective device ( can't quite recall how to test that particular circuit). Once the three phase has been tested for continuity, polartity and ins resistance, move onto the single phase board, think my zs for the from my three phase board feeding the db becomes my ze or zb for single phase board. Is that correct? oh read somewhere on one forum that testing a three phase board, has some kind of multiplying factor of 2 can't quite recall what for though.. So much to try and get my head around ( The course starts in two weeks, so looks like it's revision and past papers, that's if i can get hold of any. Picked up the two books mentioned today, so cheers for the shout on that one folks..

trev · Nov 4, 2011

There are threads in the stickys, one is mentioned above-2391 practical help another is-basic test procedures.
Read them and stick in with GN3, do the past papers, ask questions in class and here and you'll be fine.
I owe a few guys here a beer or 3 from when I did 2391, I'll bet you will too

SPARTYKUS · Nov 4, 2011

Factor of two is what you multiply your highest Pfc reading by to give your value to record on your PIR form or whatever over simplified excuse for a tick sheet its turned into....

scope02 · Nov 4, 2011

I just been reading the sum practical link, it's seems good , but thought there would be more on testing the three phase supply, basically a step by step guide as such, The gn3 is really good, covers all the test procedures... good shout..

johnelectrical · Nov 4, 2011

If you are happy with single phase testing just think of each of the three lines going to the motor as three individual single phase circuits, they all have their own line on the schedule of test results, all dead tests including bonding (there are exceptionally few situations where you will find an earth bond) cpc's of radial circuits, ring continuity, polarity are exactly the same. when it comes to Ze you have three lines so three values for Ze. you just recoed the highest. as for PFC this is different from single phase. for starters you must connect the earthing conductor, it generally doesn't matter if the installation is on or not as most modern testers compensate so unlike Ze where the installation must be off because you have disconnected the incoming earthing conductor, when doing PFC the earthing conductor must be connected so the installation does not need to be off. PFC is actually 2 tests = PeFC that is Prospective earth fault current, measured between line and earth, and PSCC prospective short circuit current, measured between live conductors (line to line or line to neutral) in a single phase install you measure both and record the highest, three phase is different. although we measure all three lines to earth for PeFC that is noted ONLY it is not used to record PFC, on a three phase install the biggest bang will be between two line conductors 400volts but most testers only go up to 250v so you measure between each line to neutral and double the highest. the reason for doubling the highest is about the ratio between single phase and three phase, to find three phase value you multiply single phase by the squar root of three (230 X 1.732 = 398.4 so approx 400v) so by measuring line to neutral at 230 volts and multiplying by root three that would give you an indication of the PFC if there was a short between two phases BUT there are three phases available so the biggest bang would be if you shorted out all three at the same time hence the instructions in GN3 that you measure short circuit current between the lines and neutral and double the highest. please remember you do not use PeFC at all in three phase installations even if the PeFC is measured higher that PSCC, and yes this does happen sometimes eg when a steel wire armour supply cable is used and one of the cores is the earthing conductor in parrallel with the steel armouring. on your practical safety is paramount. it is also open book so you can take your notes in with you, use bullet points just as reminders.

brucelee · Nov 6, 2011

scope02 said:
I just been reading the sum practical link, it's seems good , but thought there would be more on testing the three phase supply, basically a step by step guide as such, The gn3 is really good, covers all the test procedures... good shout..

Hi mate

SOMEWHERE i put a post into someones threaad giving you a step by step guide of all the 4 assessments I am having difficulty recolaecting which thread but if i find it i will post up

there is loads of useful stuff on here for 2391 try the general section in the stickys there is a thread by amberleaf and this has loads of stuff for 2391 its called section 301

read gn3 as advised fron to back back to front take it everywhere you go lol
have a read of GS38
memorandum of guidance on elecy at work regs
part 6 & 7 of the regs learn the certificates and what to call them and everything thats in them ie basic and fault protection
selv pelv, double or reinforced insualtion as everyhting to do with the certificates and completing them concerns this exam
chris kitchers practical guide to inspection and testing
exam success as this will show you how to answer the questions
earth fault loop diagrams and how to draw and label with correct terminology for every sytem TT ,Tn-s Tn-c-s IT
learn how to write out all test procedures with and without diagrams in bullet points
and for continuity of ring final circuit conductors with calculations for each step etc
jsut keep using the search bar for 2391 and you will find loads and post up any questions you may have