Hello guys. I have a question for 302 written test.

[Martin.h.lee]

I am preparing 302 written test.
One thing is confusing.

8kw 230 v cooker using T&E pvc cable directly clipped. the circuit is prtected by BSEN 60898 type B circuit breaker.
the run covers 18m. the ambient tempurature is 35 C.

With this given condition, I need to cable size, design current, fuse rating etc.
I did get the answers.
the design current is 34.8A(Ib)
the rating of circuit breaker is 40A(In)
minimum size of cable is 6 mm2

However, one of questions is that "the eath fault loop impedance Zs is 1.12 ohm; does the circuit comply with Bs7671?

I got Zs(max) value 1.15 ohm (from table 41.3 of bs7671), and the measure Zs value is 1.12
Does it complies? The given answer is 'YES'
But I think I need to apply the rule of thumb : Zs> 0.8 X Zs(measured).
If I apply the rule of thumb, then it doesn't comply.

What is your opinion?

I hope I made myself clear for the question.
Thanks

 

[Geoffsd]

I don't really know how to answer this.

It is all correct without using diversity.
However, with a cooker, diversity is always used.

A cooker of double the rating could easily be fitted and, without diversity, that would make the results formidable.

As I keep saying -
The R1 + R2 of 18m of 6/2.5mm² after Ca works out at 0.20Ω.
This would leave the Ze as 0.92Ω - not acceptable.

Perhaps it was just a poorly thought-out question.
There's no mention of the socket in the question.
If it's just en exercise to see if you can get the correct answer, then ok but if your career depended on the outcome then querying it could be good.