2391-52 exam question

[Seath]

Hello,
Would anyone be able to help with this question I do not seem to have the knowledge to answer please?

44
Questions 40 to 46 relate to the following scenario.
Insulation resistance has been tested on five new lighting circuits in an existing large
distribution warehouse. These circuits are supplied from a new single-phase, five-way DB.
Switching for each circuit is by 230 V contactors. Connection to each light is made using a
BS 1363 socket-outlet adjacent to the fitting.
The supply and installation form a 400 V three-phase TN-C-S system.
The following test results were recorded.

Circuit Line-line ohms Line-earth ohms
1 190 176
2 187 20
3 157 162
4 122 134
5 172 178

Initial and Periodic Inspection and Testing of Electrical Installations (2391-052)
Sample Questions
17What is the value of insulation resistance between Live and Earth for the new DB with all
the lighting circuits connected?

a)13 MΩ
b)20 MΩ
c)134 MΩ
d)178 MΩ

Response: correct answer is (a) I said (c)

Thanks in advance hope Duncan

 

[SparkyChick]

Can you show how you worked out the answer?

I could give you the answer but that's not going to help much as it won't expand your understanding.

 

[westward10]

The correct answer is about 13.34

 

[telectrix]

if you look at the question. reading #2 shows 20. therefore the global resistance must be <20. (resistances in parallel.). therefore a. is correct without any working out.

 

[westward10]

if you look at the question. reading #2 shows 20. therefore the global resistance must be <20. (resistances in parallel. therefore a. is correct without any working out.

No calculation required then, see I didn't spot that

 

[telectrix]

No calculation required then, see I didn't spot that

specsavers late night opening is Friday.

 

[Taylortwocities]

The ability to know about parallel resistances is a basic fundamental of electrical work..
I'm not knocking the OP, but surely this is first lesson stuff.

 

[Andy78]

On a positive note, at least now you know what you don't know, and knowing that is better than knowing nothing.

Time to revise resistance in parallel.

 

[Loki]

Rt = 1/r1 + 1/r2 + 1/r3 etc
Then the above is 1/r to give answer

 

[The Ghost]

The question states the value of IR results as ohms not Mohms would that make a difference to anyones answer? Must have forgotten to take the lamps out.

 

[Wilko]

The question states the value of IR results as ohms not Mohms would that make a difference to anyones answer? Must have forgotten to take the lamps out.

I just took it for granted as rubbish wording and they meant megs

 

[oracle]

The answer is easy but don't they give you marks for showing how you get the answer?

 

[telectrix]

it's a tick box. no working out erqiuered,

reqiured.
required.
bloody beer.

 

[westward10]

None of them are actually the correct answer, it is 13.34 what are these courses coming to.

 

[oracle]

No working out? Bloody hell have they devalued the exam completely? The old 2391 written exam was a real bugger .

 

[Andy78]

No working out? Bloody hell have they devalued the exam completely? The old 2391 written exam was a real bugger .

City and guilds were losing out to EAL whose own testing and inspection course was open book, so city and guilds dumbed down to match.

The old 2391 was split into the 2394 (initial verification) and 2395 (periodic inspection) to better serve the short course industry. Candidates only needed the 2394 bit and stood a better chance of passing just half of the content. Multiple choice elements were introduced at this stage but the main exam was still written and closed book.
They then proudly announced the "return" of the 2391 whilst failing to mention they had made it totally open book.

 

[oracle]

Who decides the standards for exams and assessments ? If City and Guilds, EAL, Logic etc can run the same course who sets the rules for the minimum requirements?

 

[Seath]

Got it now, much appreciated.
What would we do without M+ on the calculator?

 

[Andy78]

Got it now, much appreciated.
What would we do without M+ on the calculator?

Use the 1/x button ?

 

[telectrix]

what does the M+ button do? i seen it but never used it.