03
09/2020
Huanet Cable: How to Calculate the CurrentCarrying Capacity of Cables
We understand that calculating the currentcarrying capacity of cables can be challenging. Huanet Cable is here to share a simple estimation formula to help you solve this problem with ease:
Multiply 2.5 by nine,
Go up by one and subtract in line.
Thirtyfive times threepointfive,
Pair by pair, subtract pointfive.
Adjust for changes in condition,
High heat: take 90%, for copper, upgrade a level.
For conduits with two, three, or four wires,
Multiply by 80%, 70%, 60% for full load currents.
Explanation:
This formula calculates the currentcarrying capacity (safe current) of various insulated wires (rubber and plastic) by multiplying the crosssectional area by a specific factor, derived through quick mental calculation.
Multiply 2.5 by nine, go up by one and subtract in line:
For aluminumcore insulated wires with a crosssection of 2.5 mm² or less, the currentcarrying capacity is approximately 9 times the crosssectional area. For example, a 2.5 mm² wire can carry 2.5 × 9 = 22.5 A.
For wires with a crosssection of 4 mm² and above, the multiplier decreases by 1 as the wire size increases:
4 mm²: 4 × 8
6 mm²: 6 × 7
10 mm²: 10 × 6
16 mm²: 16 × 5
25 mm²: 25 × 4
Thirtyfive times threepointfive, pair by pair, subtract pointfive:
A 35 mm² wire has a currentcarrying capacity of 3.5 times its crosssectional area: 35 × 3.5 = 122.5 A.
For wires of 50 mm² and above, the multiplier decreases by 0.5 for each pair of wire sizes:
50 mm² & 70 mm²: 3 times the crosssectional area
95 mm² & 120 mm²: 2.5 times the crosssectional area
And so on.
Adjust for changes in condition, high heat: take 90%, for copper, upgrade a level:
The formula is based on aluminumcore insulated wires exposed at an ambient temperature of 25°C.
If the ambient temperature is consistently above 25°C, reduce the calculated currentcarrying capacity by 10%.
For coppercore insulated wires, calculate the currentcarrying capacity as if the wire were one size larger in aluminum. For example, the capacity of a 16 mm² copper wire is equivalent to that of a 25 mm² aluminum wire.
For conduits with two, three, or four wires, multiply by 80%, 70%, 60% for full load currents:
When wires are installed in conduits with two, three, or four wires, the currentcarrying capacity should be adjusted to 80%, 70%, or 60% of the calculated value for a single wire, respectively.