By Dave Miller · off-grid sparky · 22 years wiring solar, batteries and sheds in central QLD
“I once melted a 50mm cable on a 12V bank in a QLD summer shed because I ignored voltage drop, costing me $800 and a week of power.”
— Dave. Measure twice, buy once.
ArticlesCalculatorsSite PlannerShopBattery cable sizing in Australia must follow AS/NZS standards and account for voltage drop over distance. Undersized cables melt, waste energy and risk fire, as one QLD owner discovered after a $800 failure. Correct sizing on a 12V bank protects gear and stops cash going up in smoke.
Your off-grid system runs on battery power. If your cables are too small, you lose money, waste energy, and risk a fire. Stop being cheap. Size them properly.
Your off-grid system runs on battery power. If your cables are too small, you lose money, waste energy, and risk a fire. Stop being cheap. Size them properly.
Too small a cable = voltage drop. For 12V systems, a 3% drop is 0.36V. For 48V, it's 1.44V. That's wasted power. AS/NZS 3004.1.1:2018 says max 3% voltage drop for DC systems. Ignore this and you'll have a system that's weak and inefficient.
Use this table for 12V/24V/48V systems. Always round up to the next standard cable size. Example: 35mm² isn't standard, so go for 50mm².
| Voltage | Current (A) | Distance (m) | Min Cable Size (mm²) |
|---|---|---|---|
| 12V | 100 | 5 | 35 |
| 24V | 100 | 5 | 16 |
| 48V | 200 | 10 | 35 |
| 48V | 300 | 15 | 70 |
Source: Solar Electric voltage drop calculator. Always verify with your specific setup.
AS/NZS 3004.1.1:2018 is the law. It mandates cable sizing for voltage drop and current. Ignoring it is illegal and dangerous. Get it right or get a licensed electrician. No exceptions.
Soldering is a no-go. It's brittle and fails under vibration. Crimping is mandatory. Use the right tools (e.g., Ferguson crimp tool for $150) and lugs (e.g., 50mm² lugs for 50mm² cable). Torque terminals to 15-20 Nm. If it's loose, it'll arc and burn. Done right, it lasts years. Done wrong, you're replacing it after a fire.
Don't skimp on battery cables. It's the cheapest part of your system and the most critical. Get the right size, crimp it properly, and you'll have a reliable off-grid system for years. If you're not sure, get a licensed electrician. It's not worth the risk. Stop being cheap. Do it right.
Worth a watch: Wire Sizes Explained for Mobile, Marine & Off-Grid Electrical Systems · EXPLORIST life Mobile Marine & Off-Grid Electrical
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.
