The permissible capacity of the wire is also called the safety of the wire or safety current value, the general maximum permissible working temperature of the wire is 65 degrees, if more than this temperature, the insulation of the wire will be rapidly aging, deterioration and damage, and even cause a fire, the so-called permissible conductor capacity is the operating temperature of the wire does not exceed 65 degrees can be a long time. Through the maximum current value.
Due to the operating temperature of the wire and the wire through the current, but also with the wire cooling conditions and environment, so the wire is not a fixed value of the permissible current-carrying capacity, the same wire with a different laying method, or in different ambient temperatures, the permissible current-carrying capacity is also different, the general principle of the ambient temperature of +25 degrees when the cross-section of 1 square millimeter of the air-compartmented current of 20 A, but As it relates to the different ways of laying, through the current is not the same.
2. Selected by the mechanical strength
When the load is too small, if the permissible current-carrying capacity calculated by the size of the selected conductor cross-section, fine wire often can not meet the requirements of the mechanical strength, prone to break the line of accident, so for indoor wiring core minimum allowable cross-section of a special provision, the specific provisions of the current used to measure the.
3. Allowable voltage loss by line selection
If the wiring line is long, the conductor cross-section is too small, may result in excessive voltage loss, which will make the motor power or heat burned, the lamp luminous rate is also greatly reduced, so the general voltage of the electrical equipment or lighting equipment, electric motors and lighting equipment should not be less than 95% of the rated voltage.