This guide concerns the current-carrying capacity of cables for use in photovoltaic systems, off-grid setups, and backup power systems.

DC - Current-carrying capacity of copper wires (Cu)

❗When ordering cables, especially from China, make sure you are purchasing wires made of pure copper, not so-called copper-clad wires (i.e., aluminum wires coated with a layer of copper). Copper-clad wires have significantly worse conductivity and heat up more quickly, which under higher loads can lead to overheating and, in extreme cases, to electrical fires. Always check the product specification and request proof of material authenticity (e.g., quality certificates). Investing in verified suppliers and high-quality copper wires ensures safety and longer durability of your installation. Don’t save on safety!

Wire cross-section (mm²)	Resistance (Ω/m)	Max current (A)	Loss at 15 A (W)	Loss at 30 A (W)	Loss at 100 A (W)	Loss at 200 A (W)
4 mm²	0.004375	30 A	0.98 W	3.94 W	✖	✖
6 mm²	0.002917	40 A	0.66 W	2.63 W	✖	✖
10 mm²	0.00175	70 A	0.39 W	1.58 W	✖	✖
16 mm²	0.001094	100 A	0.25 W	0.98 W	10.94 W	✖
25 mm²	0.0007	150 A	0.16 W	0.63 W	7.00 W	✖
35 mm²	0.0005	200 A	0.11 W	0.45 W	5.00 W	20.00 W
50 mm²	0.00035	250 A	0.08 W	0.32 W	3.50 W	14.00 W
70 mm²	0.00025	300 A	0.06 W	0.23 W	2.50 W	10.00 W

DC - Current-carrying capacity of aluminum wires (Al)

❗Although aluminum wires are lighter and cheaper than copper ones, they have higher resistivity, which means they can heat up easily under higher current loads. In case of overload or short circuit, these wires pose a higher risk of overheating and insulation ignition, which is a potential fire hazard. Due to these properties, aluminum wires are recommended only as underground cables, where the fire risk is mitigated by the surrounding soil layer. For above-ground installations or those inside buildings, copper wires are preferred. Always follow safety standards and choose wires that suit your installation’s characteristics to minimize risk.

Wire cross-section (mm²)	Resistance (Ω/m)	Max current (A)	Loss at 15 A (W)	Loss at 30 A (W)	Loss at 100 A (W)	Loss at 200 A (W)
4 mm²	0.0275	20 A	6.19 W	✖	✖	✖
6 mm²	0.0183	30 A	4.12 W	16.47 W	✖	✖
10 mm²	0.0110	50 A	2.48 W	9.90 W	✖	✖
16 mm²	0.0069	70 A	1.55 W	6.23 W	✖	✖
25 mm²	0.0044	90 A	0.99 W	3.96 W	✖	✖
35 mm²	0.0032	120 A	0.72 W	2.88 W	32.00 W	✖
50 mm²	0.0022	150 A	0.50 W	2.00 W	22.00 W	✖
70 mm²	0.0016	200 A	0.36 W	1.44 W	16.00 W	64.00 W
150 mm²	0.001	300 A	0.23 W	0.90 W	10.00 W	40.00 W

AC - Current-carrying capacity of YdY copper cables

❗When ordering cables, especially from China, make sure you are purchasing cables made from pure copper and not so-called copper-clad cables (i.e., aluminum wires coated with a layer of copper). Copper-clad wires have significantly lower conductivity and heat up more quickly, which under higher loads can lead to overheating and, in extreme cases, electrical fires. Always check the product specifications and demand proof of material authenticity (e.g., quality certificates). Investing in trusted suppliers and high-quality copper cables is a guarantee of safety and longer-lasting installations. Do not cut corners on safety!

Cable cross-section (mm²)	Resistance (Ω/m)	AC current-carrying capacity (A)	Loss per 1 m at 1 A (W)
0,5 mm²	0.036	3–4 A	0.036 W
0,75 mm²	0.024	6–7 A	0.024 W
1 mm²	0.018	10–11 A	0.018 W
1,5 mm²	0.012	14–15 A	0.012 W
2,5 mm²	0.0074	18–20 A	0.0074 W
4 mm²	0.0046	25–27 A	0.0046 W
6 mm²	0.0031	32–34 A	0.0031 W
10 mm²	0.0018	40–45 A	0.0018 W
16 mm²	0.0012	58–63 A	0.0012 W

Calculating cable resistance

Formula for cable resistance: R = ρ × L / S, where:
R: Cable resistance (Ω),
ρ: Resistivity of the material (Ω·mm²/m),
L: Length of the cable (m),
S: Cross-sectional area of the cable (mm²).
Material resistivity:
Copper (CU): Resistivity is approximately 0.0175 Ω·mm²/m.
Aluminum (AL): Resistivity is approximately 0.0282 Ω·mm²/m.

How to calculate cable resistance:
- For copper: If the cable length is e.g., 10 m, and its cross-section is 4 mm², we calculate: $$ R = rac{0.0175 imes 10}{4} = 0.04375 \ \Omega $$
- For aluminum: For an aluminum cable of 10 m and 4 mm² cross-section: $$ R = rac{0.0282 imes 10}{4} = 0.0705 \ \Omega $$

Application:
Higher resistivity of aluminum means that aluminum cables generate greater power losses and require a larger cross-section to achieve similar properties to copper cables.

23.03.2025 - M.M. Junction.biz
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