Current-carrying power of electrical wires and corresponding air switch models

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1. **Basis for calculating the current-carrying power of electrical wires** - Firstly, it should be clear that the current-carrying capacity of electrical wires is related to many factors, including the material of the wires (copper or aluminum), the cross-sectional area of the wires, the laying method (exposed laying or concealed laying), and the ambient temperature, etc.

- For copper conductors, the current-carrying capacity is generally calculated by empirical formulas (in the case of an ambient temperature of about 25 °C and exposed laying): The safe current-carrying capacity of a 1-square-millimeter copper wire is 5 - 8A. For example, for a 2.5-square-millimeter copper wire, the current-carrying capacity is approximately between 12.5 - 20A.

- According to the power calculation formula \(P = UI\) (in a household circuit, the voltage \(U = 220V\)), taking the current-carrying capacity of a 2.5-square-millimeter copper wire as 12.5A for calculation, the power it can carry is \(P = 220V×12.5A = 2750W\).

2. **Relationship between the current-carrying power of electrical wires and the selection of air switch models**

- **1.5-square-millimeter copper wire** - Current-carrying capacity: Generally around 7.5 - 12A.

- Corresponding power: Calculated according to the current-carrying capacity of 10A (\(P = UI\)), \(P = 220V×10A = 2200W\).

- Air switch selection: Generally, an air switch of C10 (type C tripping characteristic, rated current of 10A) is selected. This tripping characteristic is mainly used for non-power loads such as lighting. It will trip instantaneously when the current is 5 - 10 times the rated current, which can effectively protect the circuit from overload.

- **2.5-square-millimeter copper wire** - Current-carrying capacity: Approximately 12.5 - 20A. - Corresponding power: Calculated with the current-carrying capacity of 16A, \(P = 220V×16A = 3520W\).

- Air switch selection: You can choose air switches of C16 or C20. The C16 air switch operates normally when the current reaches about 16A, and will trip quickly when it exceeds a certain multiple (such as 8 - 10 times), protecting the safety of the circuit; the C20 air switch has a higher rated current and is suitable for situations where there may be a slightly larger current impact.

- **4-square-millimeter copper wire** - Current-carrying capacity: Roughly 20 - 32A. - Corresponding power: Calculated by taking the current-carrying capacity of 25A, \(P = 220V×25A = 5500W\). - Air switch selection: Usually, air switches of C25 or C32 are selected. For example, when using a C25 air switch, it operates stably when the line current reaches about 25A. When there is an overload or short circuit and the current reaches a certain multiple, it will quickly cut off the circuit to prevent the wire from being damaged by overheating.

- **6-square-millimeter copper wire** - Current-carrying capacity: Around 30 - 48A. - Corresponding power: Calculated according to the current-carrying capacity of 40A, \(P = 220V×40A = 8800W\).

- Air switch selection: You can choose an air switch of C40. It can meet the current-carrying requirements of a 6-square-millimeter copper wire under normal operation and certain overload conditions, effectively protecting the circuit. It should be noted that the above data are reference values under the general ambient temperature (around 25 °C) and conventional laying methods. If the ambient temperature is relatively high (such as exceeding 30 °C), the current-carrying capacity of the wire will be appropriately reduced; if it is laid in a concealed manner through pipes, etc., the current-carrying capacity will also be affected to some extent. In practical applications, factors such as the starting current of the load also need to be considered. For example, the starting current of inductive loads such as motors is relatively large, and it may be necessary to appropriately increase the rated current of the air switch to avoid misoperation.