Working current and calculation

Calculation formula for working current of electric (wire) cable: single-phase, I=P ÷ (U × cos Φ)； P-power (W); U-voltage (220V); cos Φ- Power factor (0.8); I-phase line current (A).  Three phase, I=P ÷ (U × one point seven three two × cos Φ)； P-power (W); U-voltage (380V); cos Φ- Power factor (0.8); I-phase line current (A).  Generally, the safety cutoff of copper conductors is 5-8A/mm2, and that of aluminum conductors is 3-5A/mm2. In single-phase 220V lines,  The current per 1KW of power is around 4-5A, and in three-phase load balanced three-phase circuits, the current per 1KW of power is around 2A,  In other words, in a single-phase circuit, every 1 square millimeter of copper wire can withstand a 1 KW power load; The three-phase balance circuit can withstand 2-2.5KW of power;  However, the larger the working current of the cable, the smaller the safe current that can be withstood per square millimeter.

Formula for safe working current allowed by cables

Ten times five (ten times five);  One hundred and two (more than one hundred multiplied by two);  Two five three five four three boundaries (two five times four, three five times three);  Seven zero nine five two and a half times (both the seven zero and nine five lines are multiplied by two point five);  The threading temperature is 80% off (varies with temperature, multiply the calculated safety current by 0.8 or 0.9);  Copper wire upgrade calculation (based on the same cross-section of aluminum core wire, increase by one level. If the 2.5 copper core wire is one level higher than the 2.5 aluminum core wire, calculate based on the 4mm aluminum core wire);  Add half of the bare wire (add another half based on the originally calculated safety current).