Exam question

Wally and Legh

The 0.8 factor is the normally taught figure for temperature (worst case) correction of maximum Zs. The BS7671 figures are the actual maximum, whilst the OSG (which is not important to anyone with any knowledge) is already corrected by 0.8 because anyone using it probably doesn't have BS7671 and probably wouldn't understand it anyway. I have no idea where you are getting the 1.2 from except that 1/0.8 is 1.25.  The figure used for design is then safe even under continuous maximum loading. However, if you are doing an EICR this is not the figure to use unless the cable is actually at normal operating temperature, the tabulated BS7671 figure is much more sensible as a reference. Remember too that your measured value may not be exact, you should be aware of the expected accuracy and treat the measured value accordingly.


Legh if you cannot get the correct C&G answer it is not their fault, the answers are there for anyone. However, you do need to be aware that the questions may be rather more searching of your knowledge than you feel is fair. Did you get 100% in the 18th exam? Was that because the questions were unfair? I have yet to see one that is unfair or unreasonable, all of them may well be seen in an installation.


The ultimate question is this 2391 (2395) or a design question or basic 2382? The expected answer will be different, and being multiple choice you cannot explain why.

Wally and Legh

The 0.8 factor is the normally taught figure for temperature (worst case) correction of maximum Zs. The BS7671 figures are the actual maximum, whilst the OSG (which is not important to anyone with any knowledge) is already corrected by 0.8 because anyone using it probably doesn't have BS7671 and probably wouldn't understand it anyway. I have no idea where you are getting the 1.2 from except that 1/0.8 is 1.25.  The figure used for design is then safe even under continuous maximum loading. However, if you are doing an EICR this is not the figure to use unless the cable is actually at normal operating temperature, the tabulated BS7671 figure is much more sensible as a reference. Remember too that your measured value may not be exact, you should be aware of the expected accuracy and treat the measured value accordingly.


Legh if you cannot get the correct C&G answer it is not their fault, the answers are there for anyone. However, you do need to be aware that the questions may be rather more searching of your knowledge than you feel is fair. Did you get 100% in the 18th exam? Was that because the questions were unfair? I have yet to see one that is unfair or unreasonable, all of them may well be seen in an installation.


The ultimate question is this 2391 (2395) or a design question or basic 2382? The expected answer will be different, and being multiple choice you cannot explain why.