How do you calculate the minimium size CPC for a circuit?

To calculate the minimum size of the Circuit Protective Conductor (CPC), you typically refer to the regulations or standards applicable in your region, such as the IET Wiring Regulations in the UK. The minimum size is often determined based on the size of the phase conductors, with a common guideline being that the CPC should be at least 10% of the size of the largest phase conductor for final circuits. Additionally, for specific applications or conditions, such as the presence of protective devices, other factors may need to be considered. Always consult the relevant standards for precise calculations and requirements.