BS7671 Help with some PFE questions

[clanky]

‘how is the nominal voltage at origin of an installation determined?’
I thought the answer was in the start of paragraph 313.1 and is quoted as ‘..calculation, measurement, enquiry or inspection.’ but the answer in the exam was enquiry only?

Look at the model form in Appendix 6 for EIC or EICR, look for U/Uo and read carefully

back to this one, im still confused as to why 313.1 isnt correct? ie assessment of general characteristics or is it just because the word 'installation' has been used in the question?

 

[Zerax]

You have to chalk the occasional "wrong" answer to this unfortunately.

That's probably why they won't tell you which ones you got wrong either... would open up a whole can of worms and potential legal action !

 

[timhoward]

It’s also possible your practise software has errors it in. I didn’t have any issues with ambiguous questions in the actual exam. I also know that with the effort you are putting in you will easily pass.
The only issue I had was not finding a couple of things (still got 93% though)

 

[timhoward]

Q2) ..what is excluded from the scope?
I picked Lightning Protection Systems but it seems the correct answer is Highway Street Furniture which isn’t listed in 110.2

If highway street furniture was the correct answer this is wrong. Lightening Protection systems is likely the correct answer. Occasionally you get part answers that are deemed to be incorrect by not having the whole text, so some wally might decide that unless BS EN 62305 is mentioned in the answer it isn't right....but I suspect this is a website / software error.

Q40) ...Standby Generator to provide switched alternative to public supply. Which is NOT a precaution to prevent parallel operation?
From 551.6.1 I selected ‘an arrangement with separate switches for each supply’ which was wrong.

If you read the list in the regulation you mentioned, the key thing is that in all cases you can't possibly have both supplies on at once. A separate switch for each doesn't prevent you turning them both on. The point of the regulation is that you mustn't ever be able to do that.

‘how is the nominal voltage at origin of an installation determined?’
I thought the answer was in the start of paragraph 313.1 and is quoted as ‘..calculation, measurement, enquiry or inspection.’ but the answer in the exam was enquiry only?

This one is rather horrible. I feel the word "origin" is key, if you look that up in part 2 you get "the point electricity is delivered to the installation". In general that bit isn't yours to be messing around with and inspecting/measuring and you have nothing to base calculations on.
It's a poor question in my view, and again, worse than any real-life exam question I remember.

 

[pc1966]

Q5) Which describes a Neutral Conductor?
Based on the definitions in Part 2, where it describes a line conductor as a conductor of AC OTHER than the neutral and Live Part includes a Neutral Conductor, i chose wrong. The ‘correct’ answer in the exam was ‘a line conductor’ but during the course, according to my scribbled notes, the neutral was defined as Live only.

I don't have a copy of the questions, etc, but this is one odd aspect where common usage of 'live' differs from the definitions.

Live = Any current-carrying conductor under normal use (so all but the CPC)
Neutral = A live conductors that somewhere is connected/referenced to Earth.
Line = The live conductor(s) not referenced to Earth

Indeed it really is the referencing of a current-carrying conductor to Earth that defines neutral, and how/where that is done is of course on of the key aspects of the supply.

While an IT supply may not have any reference to Earth, most of any significant power level (e.g. excluding shaver supplies) do by some high impedance so they technically can have a neutral even though a single line-Earth fault has no immediate impact on operations as normally the earthing impedance is quite high and designed to sustain such a single fault. Used for situations where you really don't want an immediate interruption if at all possible (e.g. operating theatre supply, ship electrics, etc) and it is under skilled supervision.

 

[clanky]

Apologies for the delay in replying. Ive been stuck on a brutal night shift for the last week so its been a bit of eat sleep and work...repeat. Plus i didnt receive any notifications for replys...

Anyway, huge thanks to everyone for chipping in and although im fairly confident ill pass, i just find these foibles (love that word) annoying.

 

[clanky]

If you read the list in the regulation you mentioned, the key thing is that in all cases you can't possibly have both supplies on at once. A separate switch for each doesn't prevent you turning them both on. The point of the regulation is that you mustn't ever be able to do that.

Ooops. ive just reread the question and realised my mistake! Should pay more attention.

 

[clanky]

I don't have a copy of the questions, etc, but this is one odd aspect where common usage of 'live' differs from the definitions.

Live = Any current-carrying conductor under normal use (so all but the CPC)
Neutral = A live conductors that somewhere is connected/referenced to Earth.
Line = The live conductor(s) not referenced to Earth

Indeed it really is the referencing of a current-carrying conductor to Earth that defines neutral, and how/where that is done is of course on of the key aspects of the supply.

While an IT supply may not have any reference to Earth, most of any significant power level (e.g. excluding shaver supplies) do by some high impedance so they technically can have a neutral even though a single line-Earth fault has no immediate impact on operations as normally the earthing impedance is quite high and designed to sustain such a single fault. Used for situations where you really don't want an immediate interruption if at all possible (e.g. operating theatre supply, ship electrics, etc) and it is under skilled supervision.

Thanks for the detailed answer. I appreciate the effort as not being an electrician, it all adds to my knowledge. Again, ive just reread the question and i think ive made the same mistake of trying to be too quick in doing my answers. Deep breath needed when i get round to doing the exam for real.

 

[clanky]

yay 86% !!!!! Well chuffed with that.

geddin. Now i need to find a friendly local electrician to 'train' with before i do the T&I course.