As/nzs 3008 ((install)) -

It prevents cables from overheating by matching their current-carrying capacity (ampacity) to the load.

Here’s the correct step-by-step method per AS/NZS 3008.1.1: as/nzs 3008

If multiple cables are bundled together or installed in high-temperature environments (like a roof space), their capacity must be "derated" or reduced. It prevents cables from overheating by matching their

If you only remember three things: