Hi Jai,
It really depends on the Voltage Drop question you’ve got.
For questions where the max demand is provided, you would use the max demand value in your calculations. These would normally be for dedicated circuits where max demand can be determined. For final sub- circuits consisting of lighting or GPOs, as max demand is virtually impossible to determine, you can use half the value of the circuit protection device. Thus you get the CB rating x 0.5.
Look up Clause 3.6.2 Exceptions 1 in AS3000 and that will give you the details