C&G 8202 past exam paper question. Cable calc.

[securespark]

I thought you'd contacted C & G and had it out with them.

Looks like I chased them like a terrier in vain!

 

[richardindorset]

I thought you'd contacted C & G and had it out with them.

Looks like I chased them like a terrier in vain!

Thanks for chasing them, I do appreciate it! I had hoped our lecturer might have got to the bottom of it too, but in the end, this question appeared on a past eam paper, last week.

 

[securespark]

That much I understood, and you now have the answer but not C & Gs "working out".

Or have I missed that? Do you have their reasoning behind how they got to the answer?

 

[securespark]

They are sometimes tricky to pin down.

I had a question on a 60 question 17th Edition update exam which I was struggling with. It was the way it was worded I couldn't get my head around.

Not being big-headed, but when the result came back, I'd got just that question wrong. Now, if I'd got any old pass and that question right, I'd have gone away happy, but I was miffed. I wrote to C & G and they knew which question it was, but were sure the wording was straightforward.

I wish I could remember it now, but sadly I can't.

 

[richardindorset]

That much I understood, and you now have the answer but not C & Gs "working out".

Or have I missed that? Do you have their reasoning behind how they got to the answer?

Well I have the answer sheet and the scoring method.

Here's the question:

Here's their answer:

 

[securespark]

Thank you for posting that.

So, without grouping, it would be 2.5.

Aren't there some on here that say sRCDs are no longer compliant?

 

[EFLImpudence]

Well after applying the grouping factor a CCC of 28.6A is required so 4mm² is needed instead of 2.5mm² with its maximum CCC of 27A.

I think this is purely an arithmetical exercise bearing little resemblance to reality.
4mm² is only required through the grouped area; not the whole circuit.

Why a ring?
Why 32A?
Why grouping?

There is no Method B in Table 4D5.

 

[richardindorset]

Further to this question, seeing as we're all looking at it here, they ask about earth leakage and leaky PC power suppies.

What do they mean "high integrity earth"? If the ring has its own breaker and is an independant circuit, the earth is going to be 'high integrity' anyway? Or is there some other wiring required, such as a thicker CPC?

I haven't read 543.7.2.201 yet, but this aspect hasn't been taught to us yet, so bit annoying that its in an exam and ours is coming up very soon!

 

[EFLImpudence]

https://docs.rs-online.com/1cd8/0900766b803720fd.pdf

 

[richardindorset]

https://docs.rs-online.com/1cd8/0900766b803720fd.pdf

Interesting! Thanks. Still think this is a bit advanced for level 3 exams, especially when there's no mention of it in the course notes!