Advice on a BS 7671 exam question please

[John Lundrigan]

Hi All,
I am researching advice to give to candidates for the Regs exam. I came across the following question:

1.
The fundamental principles of BS7671 state that persons and livestock shall be protected against injury as a consequence of over voltages originating from

a. motors running

b. the operation of circuit breakers

c. atmospheric events

d. voltage recovery

My understanding of the BS7671 regulations would lead me to answer (c) under Regulation 131.6.2. Knowing that only one answer is correct I would choose (c) but I feel that (b) would also be a valid answer as this would give rise to transients and also comes under the same regulation in the guise of 'switching'

Jonel

 

[Spoon]

 

[ruston]

And explained in 443.

 

[John Lundrigan]

It's nice to know that you concur with answer (c) as being correct. But what is your opinion of option (b)?

 

[Deleted account]

Over voltages do not originate from the operation of circuit breakers.
It's all in the wording.

 

[telectrix]

suppose an overvoltage could occur when switching supply. say, from mains to a genny.that might be where the switching bit comes in.

 

[John Lundrigan]

Yes, I agree that the wording is important and I'm certainly very happy that answer (c) is the only intended correct result But circuit breakers can cause very substantial electrical disturbances.

I only ask the question because I have to explain why that particular option is wrong. In most question this is very easy, but no so in this question.

 

[telectrix]

i can'tse a circuit breaker being switche on/off in the normal way causing an overvoltage.

 

[John Lundrigan]

Any break in an electrical circuit will give rise to a change of current and this will cause an induced voltage. The larger the rate at which this collapses and the part of the cycle at which the break occurs could give a disturbances. In fact any switching will have some effect that way.

 

[FatAlan]

The joys of multi-choice exams. With the BS7671 exam I take the view that it’s about navigating the BYB. Like many other multi choice exams as soon as you start thinking logically you’re on to a loser.

 

[Richard Burns]

Section 443 although mentioning switching of equipment within the installation actually only covers atmospheric overvoltage in the description.
Depending on the meaning "operation" could mean automatic or manual operation; in the case of automatic operation the overcurrent not the overvoltage is the protection this device is providing.
Motors running and voltage recovery could also lead consequentially to overvoltage against which protection presumably should be provided but again not covered by 443.
Therefore c is the most appropriate response even though the others could be considered relevant C is the most relvant.

 

[John Lundrigan]

Well said, for the examiner it is a matter of choosing distracting options that are not outrageously wrong and this question does it quite well; although recovery voltage would never exceed the normal supply.

 

[Adj]

In answer to another Peterborough colleague.

Because we are all experienced practitioners, there is always a tendency to over think these multi choice questions. This question’s purpose will be to prove that the candidate can correctly identify a defining statement, in this case 131.6.2. The correct answer will be the choice of the word(s) that appear in or are closest to that statement.

The term “atmospheric events” appears in the answer and is included in the statement of fundamental principle, whereas the other answers, although having some validity, do not.

Blimey, this is a bit pedantic for a Wednesday – think I’ll finish lunch and smack a back box into some blockwork.