To Design any electrical system there are some parameters and requirements which you should have to know. First of all, we should know that the total electrical load of the system.
What is an Electrical Load?
what is SLD?
Once you know electrical load then you have to calculate the rating of main circuit breaker and size of the cable. These two are the most important parameters. Selection of appropriate circuit breaker and cable having appropriate size complied with International electrical codes and standards like IEC, NFPA, BS, etc.