:? could anyone one tell me in easy to understand terms how to calculate the cable and breaker size , including cf's and volt drop, i have a copy of BS7671 IEE Wiring Regs but i am struggling to get my head around the long calculation to reach Zs, fault current and minimum csa of cpc .
Start by calculating the design current
Select an MCB which is higher than that of the design current
Apply the correction factors to the size of the MCB
Use this to select a cable from the appendix of the regs
Verify the volt drop doesn't exceed the maximum allowed
If the cpc is the same size as the lives then it is fine
If the cpc is smaller then you can check it with regulation 543.1 in the regs.
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