Solar Cable Size Calculator (Australia)
Free Australian solar cable size calculator. Enter voltage, current, and cable run length to get the smallest copper cross-section that meets AS/NZS 3000 and AS/NZS 5033 voltage drop limits.
Solar Wire Size Calculator
How to use this calculator
Enter four values:
- System voltage — Australian residential strings typically run at 350–600 V DC; off-grid and caravan systems use 12 V, 24 V or 48 V
- Current — maximum amps the circuit will carry (read panel Imp from the data sheet, or charge controller output)
- One-way length — cable distance in metres from the array to the inverter or charge controller
- Max voltage drop % — 3% is the CEC recommendation for DC strings, 2% is excellent
The calculator returns the smallest cable cross-section that keeps drop within target. Smaller cable is cheaper at Australian copper prices and easier to terminate in MC4 connectors and inverter input blocks.
Why cable sizing matters more in Australia
Australian rooftops bake harder than almost anywhere else in the world. A cable that’s marginally undersized has three failure modes:
- Wastes solar yield — losses scale with current squared, and Australian arrays are typically the highest-yield in the world
- Drops MPPT efficiency — high drop pushes the string outside the inverter’s optimal voltage window, especially on cool, high-irradiance mornings
- Cooks insulation — colorbond roof spaces can hit 70°C ambient on summer afternoons, and undersized cable adds I²R heating on top
Going one cross-section larger than the bare minimum is the cheapest 25-year insurance policy on a CEC-installed system.
The voltage-drop math
The calculator iterates through every standard Australian cross-section (1.5, 2.5, 4, 6, 10, 16 mm² and larger) and computes the voltage drop for your inputs. It picks the smallest cable that meets your specified percentage.
V_drop = 2 × Length(m) × Resistance(Ω/m) × Current(A)The factor of 2 covers the round-trip — current goes out through the positive conductor and returns through the negative. Resistance values come from AS/NZS 3008.1 Table 35 for copper at 75°C operating temperature.
| Cross-section | Ω/km @ 75°C |
|---|---|
| 1.5 mm² | 14.5 |
| 2.5 mm² | 8.87 |
| 4 mm² | 5.52 |
| 6 mm² | 3.69 |
| 10 mm² | 2.19 |
| 16 mm² | 1.38 |
| 25 mm² | 0.870 |
AS/NZS 3008.1 uses 75°C as the design operating temperature for most domestic installations — higher than the 25°C used in some European tables, which is why Australian cable sizing tends to be conservative.
Typical Australian PV cable sizes
| Run length | 5 A | 10 A | 20 A | 30 A |
|---|---|---|---|---|
| 5 m | 2.5 mm² | 2.5 mm² | 4 mm² | 6 mm² |
| 10 m | 2.5 mm² | 4 mm² | 6 mm² | 10 mm² |
| 20 m | 4 mm² | 6 mm² | 10 mm² | 16 mm² |
| 30 m | 6 mm² | 10 mm² | 16 mm² | 25 mm² |
Assumes 3% drop on a 48 V DC system, AS/NZS 3008.1 Table 35 resistances. Higher string voltage cuts cable size dramatically — a 500 V string at the same kW carries roughly one-tenth of the current.
Voltage drop versus ampacity — both matter
AS/NZS 3008.1 sets two separate constraints:
- Ampacity — the cable must carry the current safely without exceeding insulation temperature limits, with derating for ambient, grouping and installation method
- Voltage drop — the cable must keep the load voltage within design tolerance
For long roof-to-inverter or array-to-battery runs, voltage drop usually wins. For short, high-current battery-bank cables, ampacity wins. Use the larger of the two requirements. This calculator handles voltage drop — confirm ampacity from AS/NZS 3008.1 Table 4 or equivalent with appropriate derating factors.
Australian standards you must comply with
- AS/NZS 3000:2018 — the Wiring Rules
- AS/NZS 5033:2021 — PV array installation
- AS/NZS 4777.1:2016 — grid connection of inverter energy systems
- AS/NZS 4509.1 — stand-alone power systems
- AS/NZS 3008.1 — cable selection (current-carrying capacity, voltage drop)
- AS/NZS 5139:2019 — battery installation
Only a CEC-accredited installer can sign off systems eligible for the Small-scale Renewable Energy Scheme (SRES) STC rebate. Your accredited installer must provide a written cable-sizing calculation as part of the design pack — demand it before commissioning.
What it costs to get cable wrong
A typical 6.6 kW Australian residential system installed in 2026 costs AUD 5,500–9,000 turnkey including STC discount (Clean Energy Council Solar PV Price Index, SunWiz market data, hipages and Service.com.au quotes). Annual generation is around 9,500–11,000 kWh depending on state. A persistent 2% drop above the 3% CEC target costs roughly 200 kWh/year — about AUD 60/year at the 2026 average Australian residential tariff of 30 c/kWh. Across a 25-year warranty that’s around AUD 1,500.
Upsizing 25 m of 4 mm² to 6 mm² costs roughly AUD 80–120 in materials at Australian wholesaler prices. The economics overwhelmingly favour upsizing on any borderline calculation.
Related solar calculators
- Solar voltage drop calculator — full AS/NZS 3008.1 drop calculation
- Solar panel tilt calculator — Australian latitude tilt optimisation
- Solar panel orientation calculator — north versus east-west yield
- Solar charge time calculator — battery charging from PV
For grid-connected systems, your CEC-accredited installer must lodge connection paperwork with the local DNSP (Ausgrid, Energex, SA Power Networks etc.) and register the system with the Clean Energy Regulator for STC creation. Always demand a written cable-sizing calculation as part of the as-built design pack.