Hello,
The process is :
1º Calculate de current in the circuit
2º Get a cable manufactures Current rating tables for the type of cable that you will use
3º Choose a cable with a current rating bigger than the circuit current
Iz (Imax from the cable) > Is (circuit)
you must be aware that the value in the tables are usually for 20ºC or 30ºC, so youi may have to correct the value, be also aware
that te value taken form the table is for a single cable alone, so if you have more cables together in the same conduit you must
correct the value.
4º Choose a protecion for the circuit
In > Is and In*1,45 < Iz*1,45
5º Verify that the length of the cable is not a problem for the Voltage level in the end of the circuit.
This is only some guide lines…..