By Dave Miller · off-grid sparky · 22 years wiring solar, batteries and sheds in central QLD
“After burning a 15mm cable on a 50-metre run to my shed in the heat, I learned that voltage drop kills more batteries than bad wiring ever will.”
— Dave. Measure twice, buy once.
ArticlesCalculatorsSite PlannerShopEnsure safety and efficiency with the right cable choices for your Australian power setup.
Ensure safety and efficiency with the right cable choices for your Australian power setup.
Cable sizing is critical for off-grid systems. Incorrect sizing can lead to overheating, voltage drop, or even fire hazards. AS/NZS 3008.1:2006 is the standard for Australian installations.
| Budget Tier | Cost Range (AUD) | Recommended Cables | Key Brands |
|---|---|---|---|
| Low Budget (<$100) | $50–$100 | 10mm² (for 50A), 6mm² (for 30A) | Bunnings, Jaycar |
| Medium Budget ($100–$300) | $150–$300 | 16mm² (for 80A), 10mm² (for 50A), 6mm² (for 30A) | Bunnings, Jaycar, Westinghouse |
| High Budget (> $300) | $300+ | 25mm² (for 100A), 16mm² (for 80A), 10mm² (for 50A) | Bunnings, Jaycar, Legrand |
Use these trusted products for accurate measurements and compliance:
Every job starts with AS/NZS 3008.1:2006 open on the bench. That standard covers cable selection and voltage drop calculations. I work through the tables, match conductor size to load and length, and keep voltage drop under the 5% limit. Go over that and you'll be back pulling cable.
My voltage drop calculation hasn't changed in 22 years on the tools: Voltage Drop (V) = Current (A) × Resistance (Ω) × 2. That resistance figure's not a set number—pull more cable, swap the conductor material, or step down the conductor size and it shifts on you.
Use larger cables for high currents, long runs, or high ambient temperatures to prevent overheating and voltage drop.
Test insulation resistance annually and voltage drop during peak load periods. Replace damaged cables immediately.
Exceeding 3% voltage drop is unsafe. Aim for 1–2% for critical systems like water pumps or refrigeration.
Cable sizing and voltage drop management aren't suggestions. Twenty-two years of wiring off-grid systems around central Queensland has shown me what happens when people skip the maths or buy cheap cable—fried inverters, dim lights, and unhappy customers in the middle of summer. Follow AS/NZS standards, use properly rated gear, and walk your system once a year for loose terminals or corroded lugs. Takes an hour. Cheaper than replacing a battery bank.
Twenty-two years of solar and shed wiring across Central QLD, and I've lost count of the scorched roof cavities I've pulled cable out of. DIYers reckon they can save a few bob running their own solar and battery cables, grab whatever's on the shelf at the hardware, and the next thing the insulation is melting and the house is on fire. This article lays out what goes wrong. It is not a how-to. Get a licensed sparky to do the work. AS/NZS 3000 and AS/NZS 5033 aren't suggestions — they're the standards, and the bloke who ignores them is the same bloke who ends up explaining himself to a fire investigator or a building inspector.
Worth a watch: How To Size a Wire For Off-Grid Solar Power - Calculation Examples · Cleversolarpower by Nick
While many off-grid projects are achievable as DIY, certain situations require licensed professionals:
Always check local regulations and obtain necessary permits before commencing work.