2391 revision papers and answers

[kerry]

some of the papers i have to help anyone doing the 2391-10

 

[i=p/u]

cheers

 

[ferarrifeet]

thanks.hope this helps

 

[Rumacoai]

Great stuff, thanks

 

[brav]

Q:"Explain why maximum values of earth fault loop impedance
given for agricultural and construction sites are lower than
those for ordinary installations ?
ANS:
Under 17th edition there is no longer any difference between the values used for
agricultural locations and ordinary locations. However 17
th edition has gone
RCD mad. And every agricultural electrical circuit must now be protected by
either a 30mA, 100mA or 300mA RCD. "




Q15 List three parts of the earth fault loop impedance path external to a
TN-C-S system? (3 marks)
ANS: Any three parts from the following:
1) Neutral supply conductor.
2) Earthed centre point of Star supply transformer.
3) Transformer
[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]line [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman][/FONT][/FONT]winding.
4)
[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Line [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman][/FONT][/FONT]supply conductor.

Does anyone think these answers are correct? the second question they have given Neutral supply conductor as an answer, wouldnt this be a TNS not TNCS?

 

[mickeyo]

thank you for this

 

[sam80]

Thanks a great help

 

[Kyle Chadwick]

cheers for these pal major help fresh out of my time and want to get as much revision on the 391 before applying for it

 

[morph]

b) Give two reasons for correcting maximum tabulated values of
earth fault loop impedance so that a comparison with measured
values can be made ?
ANS:
1 This is because the values referred to in BS:7671 are based on the
assumption the circuit conductors are at their „normal‟ operating
temperature. In actual practice during inspection and testing it is often
difficult to know the exact temperature of the conductors so a reduced
value of maximum earth fault impedance is applied to err on the side
of safety. (1 mark)
2 The 0.8 „rule of thumb also allows for the possibility of an error of
a smaller c.p.c being installed than is necessary and again errs on the side of safety.


really !!

 

[the_evil_edna]

cheers

 

[Nanthakumar]

some of the papers i have to help anyone doing the 2391-10

Sorry I can’t download this Pdf

 

[DPG]

Sorry I can’t download this Pdf

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