Determining Minimum Trunking Size

[Zac Allingham]

Hi im new to this forum and I am currently doing my 2357 for my apprenticeship. im struggling with some questions, 1 of which is:

A trunking run within the electrical switch-room area is to contain the following single-core thermosetting stranded cables

• 35 x 1.5mm2
• 25 x 2.5mm2
• 12 x 4.0mm2
• 10 x 10.0mm2
• 5 x 16.0mm2

Determine the minimum trunking to be used.

230/400 V TN-C-S

Ze 0.12 ohms

PFC 3.5KA

if anyone can help I would really appreciate it.

 

[Zeespark]

The answer to that is in the Onsite Guide

Andy Guinness

 

[NozSpark]

I'm sorry, but we aren't here to do your homework for you...

If you have a go showing your workings we'll let you know how you've done and point you in the right direction

Conduit and trunking factors are in the regs book (or certainly in the OSG)

 

[Zac Allingham]

well im here as a last resort and I wasn't asking for the answer I was asking for help, because im not sure how to do this question.

using the onsite guide I got the size of the trunking as 150 x 38, but I was told that wasn't right.

 

[Andy™]

how about trying to answer it yourself. then someone will tell you if its right or where you went wrong. we are not going to do your homework for you

 

[Zac Allingham]

Right, well this is what I worked out but im not sure this is the way to  go:

(35 x 1.52)+(25 x 2.52)+(12 x 42)+(10 x 102)+(5 x 162)=2707

in the OSG the closest factor I could find is 2999 and the dimensions is 150 x 38 but I was told this isn't correct and to be honest I don't think this is the right method of finding the answer.

if someone can tell me what im doing wrong that would help me out a lot

 

[NozSpark]

Each cable will have a conduit/trunking factor that is determined by it's CSA,, find that and then multiply it by the number of cables of that size (do this for each size of cable),, add them together and then find the trunking size by looking in the table for the resultant (total) conduit/trunking factor

 

[Zac Allingham]

so for a example a cable with 1.5mm2 has a cable factor of 8.6.

8.6 x 35 = 301

is that along the right lines?

 

[NozSpark]

Yep,,, do that for all of them and add them together

 

[Zac Allingham]

Thanks a lot this has really helped me out

 

[NozSpark]

So what size trunking do you have now?

Scoobs are good

 

[Zac Allingham]

ive worked out the overall factor as 1256. The closet factor I can find, which is higher, is 1542, so the trunking size is 100 x 38

1407.2 even. I messed up on one of them but still the closet is 1542 so the size is 100x38

 

[Andy™]

got there in the end, at least you now know where you went wrong and what to do. now do you really think you would know that if someone just give you the answer?

 

[Zac Allingham]

I wasn't asking for the answer in the first place, I was asking for help If u read the bottom of what I said

 

[NozSpark]

But its really difficult to help if we can't see where you've gone wrong

 

[Zac Allingham]

I appreciate that and I showed my workings. anyways thanks a lot for the help that's all I needed to know

 

[Manator]

I wish that was all I needed to know, I am still learning little things each and every day.