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Cables in conduit calculator
How many cables fit a conduit, the smallest conduit for your cables, and a quick chart.
Cables in conduit
How many cables fit, and the smallest conduit for yours.
- Most that fit a 20 mm conduit
- 7 cables
- 4 × 2.5 mm²
- Fits
- Fill
- 20.4% of 40% allowed
- Smallest conduit for 4
- 16 mm
Method
- Conduit inside diameter 16.4 mm → area 211 mm²
- Cable overall diameter 3.7 mm → area 10.8 mm²
- Allowed: 50% for 1 cable, 33% for 2, 40% for 3 or more
Reference
- AS/NZS 3000 Appendix C (cables in conduit, space factors)
- Conduit wall thickness: AS/NZS 2053.1 (Vinidex catalogue)
- Cable diameter: manufacturer datasheet for single-core insulated (unsheathed)
Notes
- Indicative. Cable diameters vary by make, so check the cable maker's data or the Appendix C tables for the job.
- Long runs and several bends make pulling harder: go up a size if in doubt.
Estimate only. Check it against the standards and the site before you rely on it. You're responsible for your work.
Quick chart: most cables per conduit
Single-core insulated (unsheathed) in rigid pvc, medium duty (grey). Change the conduit or cable above to switch the chart.
| Cable | 16 mm | 20 mm | 25 mm | 32 mm | 40 mm | 50 mm |
|---|---|---|---|---|---|---|
| 1.5 mm² | 6 | 10 | 17 | 30 | 48 | 77 |
| 2.5 mm² | 4 | 7 | 13 | 22 | 36 | 57 |
| 4 mm² | 3 | 5 | 8 | 14 | 23 | 37 |
| 6 mm² | 1 | 3 | 6 | 11 | 18 | 29 |
| 10 mm² | 1 | 2 | 4 | 8 | 13 | 21 |
| 16 mm² | 1 | 1 | 3 | 5 | 9 | 15 |
| 25 mm² | 1 | 1 | 1 | 4 | 6 | 10 |
| 35 mm² | – | 1 | 1 | 3 | 4 | 7 |
Worked out from cable and conduit dimensions at 50% fill for one cable, 33% for two and 40% for three or more. Cable sizes vary by make: check the Appendix C tables or the cable maker's data for the job.
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