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.
Always remember that the right insulated cable must be used, correctly installed, correctly earthed, correctly protected, etc etc, as per AS3000. To get really serious about your cable selection check out www.as3008.com.