17th Edition Exam Question- help required !

[maxdog]

Alright folks, I am studying for my 17th edition exam and I have come across a question in the pastpapers I am struggling with. Anyone who can point me in the right direction on how to calculate the answer would be much appreciated.

A single phase load of 13A is supplied via a 15A BS1316 fuse isning single-core 70 degree c thermoplastic copper cables installed to method 4 (reference method B). The rating factor for grouping is 0.7 and for ambient temperature is 0.87, and overload protection is to be provided. The minimum acceptable size cable will be?
a. 1mm sq
b. 1.5mm sq
c. 2.5mm sq
d. 4 mm sq

 

[roukel01]

Using It > In / CaCiCgCr

So 15/(0.87x0.7)

= 24.63 A

Looking at table 6D1 you'd need a 4mm cable.
I think!

 

[Mark.W]

What is the length of run? cos if it's 100m for instance then the VD is too high and 4mm wouldn't be any good!

 

[maxdog]

Thanks for the help. 4mm is the answer according to the paper I have. Where do i find table 6D1 ?

 

[kung]

Page 128 onsite guide buddy !
Regards
Kung.

P.S.
Hello and welcome Maxdog

 

[poppypiesdad]

But you cant take an onsite guide into the exam !
Jamie

 

[roukel01]

What is the length of run? cos if it's 100m for instance then the VD is too high and 4mm wouldn't be any good!

A valid point, but 4mm was the largest cable to choose from. Normally regs calc questions never get too complicated because you only get 2 mins per question

 

[jpmiff]

if its the c&g 2382 exam your are going to take you are allowed to use unmarked copies of both the OSG and the red book in the exam.

all you need to know is how to find the answers in the books

in the big red book, have a look at appendix 4,section 5, determination of the size of cable to be used.
becouse the question relates to a grouping factor use equation 2 on page 257.
determine It,
then select the relavent current carrying capacity table to suite the cable bing used, table4D1A in this case,
reference method B 2.5mm2=24 amps, 4mm2=32 amps

It=26amps choose cable 4mm2

hope this helps