Voltage Drop Calculator per AS/NZS 3008.1.1:2017 for Industrial Installations
Industrial voltage drop under AS/NZS 3008.1.1:2017 is limited to 5% per Clause 4.4.3, measured from the point of supply to the equipment terminals. Table 25 (copper) and Table 26 (aluminium) provide mV/A/m values, with Table 42 supplying three-phase correction factors. Long cable runs to remote plant, motor starting currents, and power factor effects require careful analysis.
Quick Reference Table
| AS/NZS 3008.1.1:2017 Voltage Drop Data — Industrial — AS/NZS 3008.1.1:2017 (2017) | ||
|---|---|---|
| Parameter | Value / Requirement | Clause Reference |
| Maximum voltage drop | 5% of nominal (20 V at 400 V three-phase) | Clause 4.4.3 |
| Copper conductor mV/A/m | Per CSA, includes resistance and reactance components | Table 25 |
| Aluminium conductor mV/A/m | Higher values than copper for equivalent CSA | Table 26 |
| Three-phase correction factor | 0.866 applied to single-phase mV/A/m values | Table 42 |
| Calculation formula | VD = (mV/A/m × Ib × L) / 1000 | Clause 4.4.3.1 |
| Power factor correction | Separate R and X components for non-unity pf loads | Clause 4.4.3.2 |
How to Calculate Voltage Drop for Industrial Installations
- 1
Survey the cable route and measure lengths
Industrial plants often have cable runs of 100-500 m from the main switchroom to remote motor control centres, pump stations, or process equipment. Measure the actual route length along cable trays, through underground ducts, and across pipe racks.
- 2
Determine design current and power factor
Use the motor nameplate FLC or process load maximum demand. Record the power factor — industrial motors typically run at 0.8-0.9 pf lagging. For large cables above 50 mm², the reactive component of voltage drop becomes significant per Clause 4.4.3.2.
- 3
Select cable material and look up mV/A/m
Choose copper (Table 25) or aluminium (Table 26). For three-phase circuits, apply the 0.866 correction from Table 42. For cables above 50 mm², use the separate R and X columns to account for power factor: mV/A/m = R×cos φ + X×sin φ.
- 4
Calculate voltage drop for each circuit
Apply VD = (mV/A/m × Ib × L) / 1000 for each feeder and final circuit. Sum the drops from the main switchboard through any intermediate distribution boards to the load. The total must not exceed 5% (20 V at 400 V).
- 5
Evaluate motor starting voltage
For direct-on-line motor starting, calculate the voltage at the motor terminals during the starting current (typically 6-7× FLC). While AS/NZS 3008 does not set a starting voltage drop limit, motors generally require 80% of nominal voltage to develop sufficient starting torque. AS/NZS 3000 Clause 5.5 covers motor starting provisions.
- 6
Document and optimise
If the voltage drop exceeds 5%, consider upsizing the cable, relocating distribution boards closer to loads, or using parallel cable runs. For very long runs, voltage regulation equipment or on-site substations may be more economical than oversized cables.
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Calculate Voltage Drop 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) |