Voltage Drop in NZ Electrical Installations
Voltage drop occurs when current flows through a cable — the cable's resistance causes a reduction in voltage at the far end. Too much drop means appliances don't get sufficient voltage to operate correctly, and in commercial settings can cause equipment failure.
NZ Compliance — AS/NZS 3000:2018
New Zealand follows the AS/NZS 3000:2018 Wiring Rules (the "Wiring Rules"). Maximum allowed voltage drop:
| Circuit type | Maximum voltage drop |
|---|---|
| Final sub-circuits | 3% of supply voltage |
| Mains and sub-mains | 1% of supply voltage |
For a 230V single-phase supply: - Final circuits: max 6.9V drop - Mains: max 2.3V drop
Formula Used
This calculator uses the standard resistive formula:
Vd = 2 × I × L × R
Where I = current (amps), L = one-way cable length (metres), R = resistance per metre of conductor (Ω/m).
Note: this is a simplified resistive calculation. For large cable sizes or long runs, reactance also plays a role — refer to AS/NZS 3008.1.1 for full de-rating tables.
All Electrical Work Must Be Done by a Registered Electrician
In New Zealand, electrical installation work must be carried out by a licensed electrician and covered by a Certificate of Compliance (CoC). WorkSafe NZ enforces this under the Electricity Act 1992.