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There is a mnemonic for the current-carrying capacity in copper-core wires and cables: multiply 2.5 by 9, then subtract 1 for each higher rating. Thirty-five times 3.5, pair them up and subtract 0.5. If conditions change, a discount is applied; at high temperatures, copper gets a 10% discount and is upgraded. Two, three, four roots pass through the tube; at 80%, 70%, 60% load, full current flow. Brief explanation: This set of formulas does not specify the current-carrying capacity (safe current) for various insulated wires (rubber- and plastic-insulated wires) directly; instead, it is expressed as \"the cross-sectional area multiplied by a certain factor\", which can be calculated mentally. “\"2.5 down multiplied by 9, subtract one and move upward\" refers to aluminum-core insulated wires with cross-sections of 2.5 mm and below; their current-carrying capacity is approximately 9 times the value of their cross-sectional area. For example, a 2.5mm” wire has a current-carrying capacity of 2.5×9=22.5(A). The multiple relationship between the current-carrying capacity and the number of cross-sections for wires of 4 mm” and larger is arranged in ascending order of wire size, with the multiple decreasing by 1 at each step: 4×8, 6×7, 10×6, 16×5, 25×4. “\"Thirty-five times 3.5, in pairs subtract 0.5,\" means that the current-carrying capacity of a 35mm” wire is 3.5 times the area of its cross-section; that is, 35×3.5=122.5(A). For wires of 50 mm” and larger, the multiplicative relationship between current-carrying capacity and cross-sectional area changes such that wire sizes are grouped in pairs, with the multiplier decreasing by 0.5 for each subsequent pair. That is, the current-carrying capacity of 50, 70 mm” wires is 3 times the cross-sectional area ； 95, the current-carrying capacity of 120mm” wires is 2.5 times their cross-sectional area, and so on. “If conditions change, a discount is applied; at high temperatures, a 10% discount applies and the copper grade is upgraded. The above formula is established for aluminum-core insulated wires installed exposed, under an ambient temperature of 25°C. If aluminum-core insulated wires are installed exposed in areas where the ambient temperature remains above 25°C for extended periods, the current-carrying capacity of the wires can be calculated using the method outlined above, and then that value should be reduced by 10% ； When insulated copper wires are used instead of aluminum wires, their current-carrying capacity is slightly higher than that of aluminum wires of the same specification; the current-carrying capacity can be calculated by using the method outlined above, by increasing the wire gauge by one level compared to aluminum wires. For example, the current-carrying capacity of a 16 mm” copper wire can be calculated based on a 25 mm2 aluminum wire.