Example: 3 × 6mm² TPS cables = 3 × 78.54 = 235.6 mm². 235.6 ÷ 0.4 = minimum internal conduit area. Step 4: Select conduit size Use the internal diameter (ID) of Australian standard conduits (usually to AS/NZS 2053).
1. The Governing Standard In Australia, conduit sizing is not a simple "one-size-fits-all" calculation. It is governed by AS/NZS 3000 Clause 3.11 (Selection and installation of wiring systems) and AS/NZS 3008.1 (Electrical characteristics).
Example: A 6mm² TPS (Twin + Earth) flat cable might have a major diameter ~10mm. Area = 10² × 0.7854 = per cable. Step 3: Apply the 40% fill Required conduit internal area = (Total cable area) ÷ 0.4
| Nominal Conduit Size (mm) | Approx. Internal Diameter (mm) | Approx. Internal Area (mm²) | Max 40% Fill Area (mm²) | |---------------------------|--------------------------------|----------------------------|--------------------------| | 16 | 12.5 | 123 | 49 | | 20 | 16.1 | 203 | 81 | | 25 | 20.7 | 336 | 134 | | 32 | 26.6 | 556 | 222 | | 40 | 33.4 | 876 | 350 | | 50 | 42.4 | 1,412 | 565 |
From the example above (589 mm² needed), you would select . 4. Practical Australian Reference Table (Common Cables) These are approximate maximums for short, straight runs (under 10m, minimal bends). For long runs or multiple 90° bends, drop one size.
