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Two 2.5mm² wires twisted together can be used. It is approximately equivalent to 4.5mm². The premise is that the material must be the same, and the length must also be the same. Using two wires with the same cross-section in parallel is common in work and maintenance.
Generally, for small cross-sections (below 10mm²), this method is not recommended or commonly used. It is most often applied in power distribution, where large cable sizes are difficult to install. In such cases, two cables of the same material and length are used in parallel to solve the problem. As long as the material and length are the same, the current-carrying capacity of two identical wires can match that of a single wire.
If two 2.5mm² wires and one 5mm² wire are of the same length and material, then the current-carrying capacity of the two 2.5mm² wires twisted together and connected in parallel should be about the same as the single 5mm² wire (or possibly even slightly better).
Because the combined safe current-carrying capacity of two 2.5mm² copper wires is roughly equivalent to that of a 6mm² copper wire.
The use of two or more wires in parallel can occasionally be seen. For example, in 220kV high-voltage transmission lines, each phase is composed of two wires in parallel. Between towers, the two wires are separated, but around the towers, they are combined together.
For 500kV high-voltage transmission, there are even cases where four wires are connected in parallel for one phase.
So, two 2.5mm² wires twisted together and connected in parallel should be able to replace a single 5mm² wire.
However, connecting two wires together does not guarantee an even split of current. Because it’s impossible to ensure both wires are exactly the same length or have precisely the same internal diameter, one wire may carry more current than the other. The one carrying more current is likely to heat up and may burn through its insulation.
For example, a 10mm² wire is made up of seven copper strands intertwined, and they share current evenly. But two separate 2.5mm² wires each have their own insulation, so they cannot share current internally, which can lead to uneven distribution and insulation damage.
Of course, for temporary or short-term use, this is not a big issue. But for long-term use, it is still better to buy a thicker wire!
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Jiangxi Zhongtebang Cable Co., Ltd.