Assignment help

[Siam]

Determine the minimum size of cpc for the circuit giving consideration to; Disconnection times Thermal Constraints?

Here is what I have worked out so far for the circuit -

Ib=p/(Ulx√3) = 12000/(400 x 1.732) = 17.32Amps

From Table B6 I selected a C20 which has a max Zs of 0.87 Ω
20>17.32

Cable Selection

CA=1.03 Cg=0.70

It=In/cacg= 20/1.03x0.70=27.74A

I selected a cable size of 〖4mm〗^2 with a current carrying capacity of 28A, this was found from table 4D1A from the on-site guide.

Reference method B in trunking/conduit

9.5x17.32x42/1000 = 6.91V mv/a/m x ib x L

Yes, the voltage drop does comply.

Any help would be greatly appreciated.

 

[Richard Burns]

The minimum cross sectional area permitted for a circuit protective conductor is calculated from the formula
View attachment 35719
Therefore you need either the I²t (the let through energy of the protective device)
or the prospective earth fault current and from that using the graphs in Appendix 3 (or the manufacturers data) determine the time in which the protective device will operate and select the appropriate k value for the protective conductor material (presumably copper in table 54.3) you are using.