*Note: Based on Copper conductors, V-90 insulation at 75°C. Always refer to AS/NZS 3008.1.1 for final verification.
Understanding Cable Sizing in Australia (AS/NZS 3008)
In Australia, electrical installations must comply with the AS/NZS 3000 (Wiring Rules) and AS/NZS 3008.1.1 standards. Choosing the correct cable size is not just about making the equipment work; it is a critical safety requirement to prevent fires and ensure equipment longevity.
Key Factors in Cable Selection
Current Carrying Capacity (Ampacity): The cable must be thick enough to carry the electrical current without overheating. This is affected by the installation method (e.g., in a conduit, in the ground, or in free air).
Voltage Drop: As electricity travels through a wire, some energy is lost as heat due to resistance. AS/NZS 3000 generally limits voltage drop to 5% from the point of supply to any point in the installation.
Short Circuit Performance: The cable must be able to withstand the heat generated during a fault until the circuit breaker trips.
Environment: Ambient temperature and proximity to other cables significantly affect how much heat a cable can dissipate.
Typical Cable Sizes for Australian Homes
While this calculator provides mathematical minimums, common practice in AU includes:
1.5mm²: Standard for lighting circuits (usually protected by a 10A breaker).
2.5mm²: Standard for power outlets (usually protected by a 16A or 20A breaker).
4mm² or 6mm²: Common for split-system air conditioners or ovens.
10mm² to 16mm²: Common for main supply lines in residential homes.
Calculation Example
Suppose you are running a single-phase 230V circuit for a backyard shed 40 meters away with a 20 Amp load. If we aim for a 3% voltage drop:
Allowed drop = 230V x 0.03 = 6.9V.
Using a 4mm² cable (resistance approx 11.2 mV/A/m): Drop = (20A * 40m * 11.2) / 1000 = 8.96V (Fails 3%).
Using a 6mm² cable (resistance approx 7.49 mV/A/m): Drop = (20A * 40m * 7.49) / 1000 = 5.99V (Passes).
In this scenario, a 6mm² cable would be the minimum requirement based on voltage drop constraints.
function updateVoltage() {
var phase = document.getElementById("phaseType").value;
var voltInput = document.getElementById("voltage");
if (phase === "1") {
voltInput.value = "230";
} else {
voltInput.value = "400";
}
}
function calculateCableSize() {
var phase = parseFloat(document.getElementById("phaseType").value);
var voltage = parseFloat(document.getElementById("voltage").value);
var loadType = document.getElementById("loadInputType").value;
var loadValue = parseFloat(document.getElementById("loadValue").value);
var length = parseFloat(document.getElementById("runLength").value);
var maxDropPct = parseFloat(document.getElementById("maxDrop").value);
if (isNaN(voltage) || isNaN(loadValue) || isNaN(length) || isNaN(maxDropPct)) {
alert("Please enter valid numerical values.");
return;
}
// Calculate Current (I)
var current = 0;
if (loadType === "amps") {
current = loadValue;
} else if (loadType === "watts") {
if (phase === 1) {
current = loadValue / voltage;
} else {
current = loadValue / (voltage * Math.sqrt(3));
}
} else if (loadType === "kw") {
if (phase === 1) {
current = (loadValue * 1000) / voltage;
} else {
current = (loadValue * 1000) / (voltage * Math.sqrt(3));
}
}
var allowedDropVolts = (maxDropPct / 100) * voltage;
// mV/A/m data for PVC V-90 Copper Cables (AS3008 approximation)
// Format: [Size mm2, mV/A/m value]
var cableData = [
[1, 44.8],
[1.5, 29.9],
[2.5, 18],
[4, 11.2],
[6, 7.49],
[10, 4.48],
[16, 2.81],
[25, 1.80],
[35, 1.29],
[50, 0.942],
[70, 0.672],
[95, 0.493],
[120, 0.395]
];
var recommendedSize = "Consult Engineer (>120mm²)";
var finalDrop = 0;
var finalDropPct = 0;
for (var i = 0; i < cableData.length; i++) {
var size = cableData[i][0];
var mvAm = cableData[i][1];
// Formula for Voltage Drop
// Single Phase: (I * L * mVAm) / 1000
// Three Phase: (I * L * mVAm) / 1000 (standardized tables often assume 3-phase mV/Am)
var drop = (current * length * mvAm) / 1000;
if (drop <= allowedDropVolts) {
recommendedSize = size;
finalDrop = drop;
finalDropPct = (drop / voltage) * 100;
break;
}
// If it's the last one and still not found
if (i === cableData.length – 1) {
recommendedSize = "Over 120";
finalDrop = drop;
finalDropPct = (drop / voltage) * 100;
}
}
// Display results
document.getElementById("resSize").innerText = recommendedSize;
document.getElementById("resCurrent").innerText = current.toFixed(2);
document.getElementById("resDropVolts").innerText = finalDrop.toFixed(2);
document.getElementById("resDropPercent").innerText = finalDropPct.toFixed(2);
document.getElementById("resultArea").style.display = "block";
}