That chart lies if the cable is long. This is where 90% of DIY fails happen. Part 2: The "Voltage Drop" Monster (Distance kills amps) Imagine water flowing through a hose. A short hose (10m) gives full pressure. A long hose (100m) dribbles out.
Instead of just a dry chart, this guide uses a and a "Decision Tree" to help you choose the right cable for your shed, caravan, or solar system. The Ultimate Guide to Cable Sizing (Australia): Amps, Distance & the "3% Rule" The Golden Rule of Sparkies "The breaker protects the cable, not the appliance." You must size the cable so it handles more amps than the circuit breaker rating. If your breaker is 20A, your cable must handle at least 20A (we use 25A+ for safety). Part 1: The Cheat Sheet Chart (Copper, 240V, Standard PVC Sheathed - V-90) Use this for typical house wiring, power circuits, and lighting.
| Cable Size (mm²) | Max Amps (In free air/Clipsal) | Max Amps (In wall/Conduit) | Typical Use Case | | :--- | :--- | :--- | :--- | | | 11A | 10A | 1mm is dead. Use 1.5mm for lights. | | 1.5 mm² | 16A | 14A | Lighting circuits (LEDs are fine, halogens need this). | | 2.5 mm² | 27A | 22A | Standard Power Points (10A GPOs). Your house walls. | | 4.0 mm² | 37A | 30A | Ovens, cooktops, air conditioners (up to 25A). | | 6.0 mm² | 48A | 38A | Large ovens, instant HWS, Sub-mains (shed feed). | | 10 mm² | 67A | 52A | Small switchboards, EV chargers (7kW). | | 16 mm² | 88A | 69A | Big sheds, induction cooktops. |
Over distance, voltage drops. When voltage drops, amps spike, wires melt, motors die. The 3% Rule (Australia) For power & light circuits, your voltage drop cannot exceed 3% of 240V (which is 7.2 Volts lost).