Cable calcs.

[PJF Electrical]

Ok here's one to get your teeth into....

When working out the current carrying capacity of cables (Appendix 4 BS7671 2008) do you apply maximum demand and diversity?

I can't find this in so many words in the regs and page 95, paragraph 4 Appendix 1 of the OSG contradicts itself.

 

[matt.leung]

cable cal then deversity....

 

[Andy™]

apply diversity where allowed, get your design current and then work cable calcs from there

 

[Barx]

Diversity is for the demand on the supply. It is NOT applied to final circuits. These must be designed for the full load.

 

[Andy™]

Diversity is for the demand on the supply. It is NOT applied to final circuits. These must be designed for the full load.

your a bit off there... diversity applies to the circuit. i.e lighting. your design current can be value after diversity. same with your cooker circuit.

 

[Lee321]

[quote name='Andy

 

[Markiemarque]

Here's what I was told on me level 3 :

1) Identify design current (Ib) by applying diversity to final circuit (s)

2) Select protective device (In)

3) Apply correction factors for ambient temp/grouping/insulation/cable operating temp/protective device

4) Use Regs/on-site to find suitable cable able to meet It (from stage 3)

5) Check volt drop

6) Calc Zs

 

[Andy™]

Here's what I was told on me level 3 :1) Identify design current (Ib) by applying diversity to final circuit (s)

2) Select protective device (In)

3) Apply correction factors for ambient temp/grouping/insulation/cable operating temp/protective device

4) Use Regs/on-site to find suitable cable able to meet It (from stage 3)

5) Check volt drop

6) Calc Zs

that pretty much covers it

 

[PJF Electrical]

Thank you all for the replies. I would just like to add that I know how to carry out cable calculations but it is always nice to have confirmation. However the question was "I can't find this in so many words in the regs and page 95, paragraph 4 Appendix 1 of the OSG contradicts itself. " as in "I want the official line from the IEE or similar.

I do know that Trevor Linsley quotes diversity for a cooker circuit in the level 2 (basic) book but again omits this in his level 3 book (advanced).

I can see the sense in appying diversity but need clarification.

So the challenge is out there!!

 

[Andy™]

I do know that Trevor Linsley quotes diversity for a cooker circuit in the level 2 (basic) book but again omits this in his level 3 book (advanced).

no point teaching something in level 3 that you would have been taught in level 2

 

[JUD]

[quote name='Andy

 

[ian932]

So for a 8kW cooker:8000/230 = 35A

10A + 30% of 25A (7.5A) = 17.5A

Does this mean you would wire the cooker using 1.5mm cable?

I think not!!

only if it was reference method C