Voltage Drop Calculator per AS/NZS 3008.1.1:2017 for Residential Installations
AS/NZS 3008.1.1:2017 Clause 4.4.3 limits voltage drop to 5% of nominal voltage from the point of supply to the furthest point of utilisation in residential installations. Table 25 provides mV/A/m values for copper conductors and Table 26 for aluminium. For 230 V single-phase domestic supplies, the maximum permissible drop is 11.5 V.
Quick Reference Table
| AS/NZS 3008.1.1:2017 Voltage Drop — Residential — AS/NZS 3008.1.1:2017 (2017) | ||
|---|---|---|
| Parameter | Value / Requirement | Clause Reference |
| Maximum voltage drop | 5% of nominal voltage (11.5 V at 230 V) | Clause 4.4.3 |
| mV/A/m copper conductors | Tabulated per CSA at 75°C conductor temperature | Table 25 |
| mV/A/m aluminium conductors | Tabulated per CSA at 75°C conductor temperature | Table 26 |
| Three-phase correction | Multiply single-phase mV/A/m by 0.866 | Table 42 |
How to Calculate Voltage Drop for Residential Installations
- 1
Confirm supply voltage and drop limit
For residential installations, the nominal supply is 230 V single-phase (or 400 V three-phase in larger homes). The maximum permissible voltage drop is 5% per Clause 4.4.3, giving 11.5 V for a 230 V supply.
- 2
Determine circuit design current
Calculate the maximum demand current for the circuit. For domestic circuits, AS/NZS 3000 Table C1 provides typical demand values — for example, a power point circuit protected by a 20 A circuit breaker has a design current up to 20 A.
- 3
Measure cable route length
Measure the cable route length from the switchboard to the furthest outlet. Include all vertical drops, horizontal runs through the roof space, and any deviations around obstacles. In Australian residential construction, roof space runs can add significant length.
- 4
Look up mV/A/m from Table 25
For copper conductors (standard for residential), find the mV/A/m value in Table 25 for the selected conductor size. For 2.5 mm² V-75 copper, the single-phase mV/A/m value is approximately 17.8 mV/A/m.
- 5
Calculate and verify voltage drop
Compute VD = (mV/A/m × Ib × L) / 1000. Compare against 11.5 V (5% of 230 V). If exceeded, increase conductor size to the next standard size and recalculate. Document the final cable size, route length, and calculated voltage drop.
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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) |