There are three standards for wire specifications commonly used internationally: the American system (AWG), the British system (SWG) and ours (CWG). 

  A few squares is a nominal value specified in the national standard, a few squares is the user to choose the wire and cable according to the load of the wire and cable. Wire square number is a verbal term in the renovation of plumbing construction, often said a few square wire is not added to the unit, that is, square millimeters. The square of the wire is actually marked by the cross-sectional area of the wire, that is, the area of the circular cross-section of the wire, in square millimeters. Generally speaking, the empirical load is when the grid voltage is 220V, the empirical load per square wire is about a kilowatt. Copper wire can carry 1-1.5 kilowatts per square, aluminum wire can carry 0.6-1 kilowatts per square. Therefore, the power of 1 kilowatt appliances only need to use a square of copper wire is sufficient. Specifically to the current, the general copper wire per square can carry 3A to 5A of current when the short distance of power delivery. Heat dissipation conditions are good to take 5A / square millimeter, bad to take 3A / square millimeter.

  Conversion method: know the square of the wire, calculate the radius of the wire with the formula for requesting a circular area: wire square number (square millimeters) = circumference (3.14) × wire radius (mm) square know the square of the wire, calculate the line diameter is also the same, such as: 2.5 square wire line diameter is: 2.5 ÷ 3.14 = 0.8, and then squared to derive 0.9 mm, so 2.5 square line The diameter of the wire is: 2 × 0.9 mm = 1.8 mm. Know the diameter of the wire, calculate the square of the wire is also used to find the formula for the circular area to calculate: the square of the wire = circumference (3.14) × the square of the diameter of the line / 4 cable size is also denominated in square, multi-stranded line is the sum of the cross-sectional area of each wire. The formula for calculating the cross-sectional area of the cable: 0.7854 × wire radius (mm) square × number of shares such as 48 (0.2 mm radius per wire) 1.5 square line: 0.785 × (0.2 × 0.2) × 48 = 1.5 square