An Awful Feeling This

[IQ Electrical]

i have a few past papers but i dont have the answers so i cannot refer back to check if my answers are correct

i started revising tonight at 8.30 and just finished now, up at 6 for work:frown2:

You DO have the answers, do the paper then reference your answers with Guidance Note 3.

You can even use GN3 as you do the papers if that works better.

 

[gap30]

2 questions i keep getting wrong GRRR!

State
a) two physical changes made to an installation that may result in an increase in the resistance of a circuit conductor

b) one reason, apart from a fault or deterioration, why overall insulation resistance of an installation may decrease


State three factors that affect the values of installation resistance for an electrical installation


I have got to get these two questions straight in my head i cant afford to drop any marks

 

[sparc]

Usually ohms law and resistivity equation gets you out of these, but I must admit I'm struggling here. So resistance is a function of temperature, cross sectional area of conductor and its length - so as temperature is a physical change that must be one of the first two, but I'll be damned if I can remember another one! (The temperature of the installation can go up or down, but length and csa should stay same)

Overall IR if the installation - taking all the circuits together - which is a good way of checking if you have an IR problem before looking at individual circuits - parallel conductors means lower resistance, so the more circuit the lower. And the longer a circuit, the lower the IR.

'Overall condition of the installation' can be a good catch-all, so worth trying if you're stumped for a 2nd or 3rd in these types of questions about the installation.

 

[Deleted member 9648]

2 questions i keep getting wrong GRRR!

State
a) two physical changes made to an installation that may result in an increase in the resistance of a circuit conductor....Think about the effect an increase in load current would have on a conductor.....and the effect of increasing the length of a circuit,or the cross sectional area of the conductor.

b) one reason, apart from a fault or deterioration, why overall insulation resistance of an installation may decrease....The clue is in bold,what is the result of resistances in parallell?


State three factors that affect the values of installation resistance for an electrical installation...When you are testing and get a low reading what do you look for?


I have got to get these two questions straight in my head i cant afford to drop any marks

...........

 

[gap30]

...........

when i am testing and get a low reading, i will trace the faulty leg of the circuit

this is a totally different scenario, i am finding it hard to get my head around some of the wording of these answers

sorry to be a grouch i have been revising for 3 days solid (even in work)

 

[gap30]

b) one reason, apart from a fault or deterioration, why overall insulation resistance of an installation may decrease....The clue is in bold,what is the result of resistances in parallell?

i have to admit i do not understand the term resistances in parallel

 

[brucelee]

Hi mate

all final circuits are in parallel to each other so thsi will reduce the overall IR

say you have 6 circuits
tested individually
circuit 1 299M/Ohms or greater
circuit 2 299 M/Omhs or greater
circuit 3 20M/ohms
circuit 4 2Mohms
circuit 5 299M/Ohms or greater
circuit 6 299M/ohms or greater

calc total Ir

Ie
1/Rt = 1/R1 +1/R2+1/R3+1/R4+1/R5+1/R6
1/Rt = 1/299+1/299+1/20+1/2+1/299+1/299
1/Rt = 0.003 +0.003+0.05+0.5+0.003+0.003
1/Rt = 0.562
RT = 1/0.562
=1.78M/Ohms rounded up
as you can see total IR still complies so if you had carried out the test as a whole then you would have had to check reason for low reading as its less than 2M/Ohm but still complies as greater than 1M/Ohm

and when you did start to test individually you would find the reasons for the low reading was the 2 circuits with low individual Ir
but all comply and 2 Meg or greater its ok but 2 M is low so next pir date should reflect this in order to see if further deterioration is occurring but at the minute still acceptable

 

[tommy76it]

I did 2391 written in june,when will i get results?

 

[gap30]

thanks mate, you have cleared that up for me no end, just done the exam success exam practice 1 long questions and i am still reading the questions wrong

State
a) the purpose for which this periodic inspection and test is required, as identified on the report

my answer: to verify the installation is safe for continued service

book answer: change of tenancy

worst thing is i fill these in on a daily basis, still reading questions in the wrong manner.....

also has anyone got any links to the diagrams for the earth fault loop impedance paths for tncs, tns, tt etc?

 

[IQ Electrical]

thanks mate, you have cleared that up for me no end, just done the exam success exam practice 1 long questions and i am still reading the questions wrong

State
a) the purpose for which this periodic inspection and test is required, as identified on the report

my answer: to verify the installation is safe for continued service

book answer: change of tenancy

worst thing is i fill these in on a daily basis, still reading questions in the wrong manner.....

also has anyone got any links to the diagrams for the earth fault loop impedance paths for tncs, tns, tt etc?

The fault path diagrams were in the exam success book, have they been removed?

 

[brucelee]

Hi mate Pm me your email i have some I did draw myself which i am no good at lol they were done when doing the course I have to warn you they were rushed free hand and my writing has always been shocking lol but they show all correct terminology and as the tutor showed us first lesson this sis all we did draw earth fault loop diagrams and discuss extraneous conductive parts and exposed etc

it will take me a bit to dig them out lol

 

[brucelee]

I did 2391 written in june,when will i get results?

Hi mate C&G say 42 days it took them nearly 13 weeks to send my results for written and almost 5 months nearly for the cert to arrive but it didnt help that our tutor didnt send the practical assesment papers to C&G until october i did exam june 2010 cert arrived november lol now my practical test says october i think even though i did it june 15th 5 days after written

 

[tommy76it]

Its a pain waiting for results.It will be a nightmare if i fail and have to start revising again.Pretty sure ill have done enough to get a pass though.

 

[gap30]

another one for you

state the purpose of an initial verification of a newly installed circuit

To conform that the circuit complies with the designers intentions
The circuit has been designed, installed and tested in accordance with the requirements of BS7671
It is not damaged so as to impair safety or otherwise defective

ok but guidance note 3 also says

initial verification shall be carried out to verify:

all installed electrical equipment and material is of the correct type and complies with applicable British Standards or acceptable equivalents
all parts of the fixed installation are correctly selected and erected
no part of the fixed installation is visibly damaged or otherwise defective

so which one is right?

 

[gap30]

Hi mate Pm me your email i have some I did draw myself which i am no good at lol they were done when doing the course I have to warn you they were rushed free hand and my writing has always been shocking lol but they show all correct terminology and as the tutor showed us first lesson this sis all we did draw earth fault loop diagrams and discuss extraneous conductive parts and exposed etc

it will take me a bit to dig them out lol

pm sent pal