Job and limit
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The Wiring Rules (AS/NZS 3000) allow 5% in total from the point of supply to any point, so add the consumer mains and any submains as runs too.
Your details for the report
Printed at the top of the report. Kept when you start again.
Cable runs
One row for each part of the route, from the point of supply out to the load. The drops add up.
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| Run | Volts | % | Max length | Max load |
|---|---|---|---|---|
| Total |
Max length and max load are how long that run could be, or how much current it could carry, with everything else as it is, before the total reaches the limit. Voltage drop only: check the cable’s current rating too.
How it’s worked out
- Vd = mV/A·m × I × L ÷ 1000. mV/A·m is 2 × Z for single phase (out and back) and √3 × Z for three phase (balanced load), where Z is the cable’s impedance per metre.
- Resistance is the standard maximum for the conductor size at 20 °C (IEC 60228), raised to the cable’s operating temperature. Reactance is taken as 0.08–0.1 mΩ/m, typical of multicore cables. Parallel runs share the current.
- Loads in kW are turned into amps at the voltage and power factor you enter.
A guide only. It checks voltage drop and nothing else. The cable must also carry the current where it’s installed (derating for grouping, insulation and ambient temperature), and meet short-circuit and earth fault loop impedance limits. Always check against AS/NZS 3000 and AS/NZS 3008.1.1.