Electrical Cable Size — Chart Amps Australia Work
Instead of just a dry chart, this guide uses a "Water Pipe Analogy" 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 | | :--- | :--- | :--- | :--- | | 1.0 mm² | 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. | The Trap: 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. Electricity is the same. 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). The Rule of Thumb for 240V: electrical cable size chart amps australia
2.5mm² cable: Maximum length = 30 meters (from switchboard to device). 4.0mm² cable: Maximum length = 45 meters . 6.0mm² cable: Maximum length = 70 meters .
If your shed is 80m from the house and you run 2.5mm² cable... your power tools will run slow, overheat, and your lights will flicker like a horror movie.
Voltage Drop Formula (For nerds & solar guys) VD (Volts) = (Length in meters × Amps × 0.017) ÷ mm² Example: 20A over 50m using 4mm². (50 x 20 x 0.017) / 4 = 4.25 Volts lost. (Acceptable, under 7.2V). Part 3: The Real-World Decision Tree Don't search the chart. Ask yourself these 3 questions: Q1: What is the circuit breaker rating? Instead of just a dry chart, this guide
10A breaker → Min 1.5mm² (but use 2.5mm² for power). 16A breaker → Min 2.5mm². 20A breaker → Min 2.5mm² (check distance). 32A breaker → Min 4.0mm² (usually 6mm² for safety).
Q2: How far is the run?
< 20m → Use the chart above. 20m - 40m → Go up one size (e.g., 2.5mm² → 4mm²). 40m - 70m → Go up two sizes. Part 1: The Cheat Sheet Chart (Copper, 240V,
70m → Calculate properly (AS/NZS 3008) or use a sparky.
Q3: Where is the cable?