This is the distance from the circuit protection (circuit breaker) to the load. Guessing the length can result in an undersized cable. Always factor in a bit extra for the "rise and fall" of cables in conduits and risers.
Always input accurate lengths, be realistic about the installation environment (enclosed vs. open air), and never forget to calculate for voltage drop. In Australia, we don't guess with electrical safety. If you are unsure, always err on the side of caution and go one size up—it’s far cheaper to pay for extra copper now than to tear down a wall later.
In Australia:
Or use Table 40–51 (mV/A/m values):
: The most recent update, which includes revised reference tables and values, though the core calculation methodology remains consistent. How to Use a Cable Size Calculator DC Cable Sizing using AS/NZS 3008; and Limitations -