Cable Sizing Calculator per AS/NZS 3008.1.1:2017 for Industrial Installations
Cable sizing for AS/NZS 3008 industrial installations addresses high-current motor feeders, process plant ambient temperatures up to 80 °C requiring Table 14 derating, short circuit withstand per Clause 3.7 and Table 34, and multi-circuit cable tray runs where Table 13 grouping factors significantly reduce current-carrying capacity for bundled power and control cables.
Quick Reference Table
| AS/NZS 3008 Industrial Cable Sizing References — AS/NZS 3008.1.1:2017 (2017) | ||
|---|---|---|
| Parameter | Value / Requirement | Clause Reference |
| Motor cable sizing | Full-load current rating from motor nameplate | AS/NZS 3000, Clause 4.7 |
| High ambient derating | Correction for air temps 45-80 °C in process plants | Table 14 |
| Cable tray grouping | Multi-layer derating for industrial tray runs | Table 13 |
| Short circuit withstand | k²S² ≥ I²t adiabatic equation for copper/aluminium | Clause 3.7, Table 34 |
| Buried cable in ducts | Current ratings for cables in underground ducts | Table 3, Columns 17-19 |
| Voltage drop for long feeders | mV/A/m values for three-phase industrial circuits | Table 25 |
How to Calculate Cable Sizing for Industrial Installations
- 1
Determine the motor or process load current
Obtain the full-load current from the motor nameplate or drive specification. For DOL-started motors, account for starting currents of 6-8 times FLC when selecting protective devices.
- 2
Assess the ambient environment
Measure or estimate the maximum ambient temperature in the cable route. Process plants, boiler houses, and smelters may have sustained temperatures of 50-80 °C requiring severe Table 14 derating.
- 3
Apply all derating factors
Combine Table 14 (temperature), Table 13 (grouping), and Table 22 (buried sections) factors. In industrial settings, the combined derating can reduce effective cable capacity by 40-60%.
- 4
Select cable size from Table 3
Choose the conductor cross-section where derated capacity exceeds the design current. For industrial feeders, X-90 (XLPE 90 °C) insulation is preferred for its superior temperature and short circuit performance.
- 5
Verify short circuit withstand
Use Clause 3.7 and Table 34 (k factors) to verify the cable can withstand the prospective fault current at the switchboard for the upstream protective device clearing time.
- 6
Check voltage drop under running and starting
Calculate steady-state voltage drop per Table 25 and verify motor starting voltage dip remains acceptable — typically above 80% of nominal at motor terminals.
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Calculate Cable Sizing NowBS 7671 vs AS/NZS 3008 Cable Sizing Comparison
| Parameter | BS 7671 | AS/NZS 3008 |
|---|---|---|
| Region | United Kingdom | Australia & New Zealand |
| Voltage drop limit | 3% lighting / 5% other | 5% general (AS/NZS 3000 Table C7) |
| Reference ambient temp | 30°C air | 40°C air (Table 22) |
| Ampacity tables | Appendix 4 Tables 4D1A–4J4A | Tables 13–20 (by method) |
| Derating tables | Ca, Cg, Ci, Cc factors | Tables 22, 24, 25, 26 factors |
| Soil temp reference | 20°C | 25°C (Table 25) |