Choose the right cable, according to Australian Standard AS3000. The cross sectional area (CSA) of a conductor will cause a volt drop per meter per amp. To be compliant, the cable should have no more than 5% volt drop over its total length for full load current and no more than 10% volt drop for start up current. A rule of thumb for a motor is the start up current is 5 times the full load current.
Example: You want to run a cable for a powerpoint in your shed 100m away. You may only pull 10A from a power point so that becomes the full load current. Lets say the biggest power tool you are going to run has a 1200W motor; divide that by 230(volts) gives you its full load requirement at 5.2A. Start up current for a motor is five times the full load current so the tool will draw 26A on startup. The calculator shows that although 4mm² cable is fine for the full load current, only a 6mm² cable meets the specification for start up current.
Note: Although we are dealing with 240VAC systems, AS3000 says we must do these calculations at a factor 1.04 which brings us down to 230VAC.