Wire and cable testing items and methods

　　At present, there are many and messy domestic wire and cable manufacturers, the production technology level is uneven, and the industry's quality assurance system is not perfect, resulting in a large gap between the quality of wire and cable products produced in my country and other developed countries. In addition, some manufacturers use unqualified raw materials and production processes in pursuit of high profits, which has further led to the flood of fake and inferior wire and cable products in the domestic market.

　　In recent years, the country has gradually paid attention to the problem of wire and cable testing, and formulated some strict production and quality regulations for this, which has promoted the improvement of the quality of my country's wire and cable products to a certain extent.

　　performance issues

　　A certain domestic quality inspection agency has conducted an investigation on the wires and cables of some electrical appliances. The results show that the qualified rate of the wires and cables of the manufacturers that have passed the ISO9000 certification is below 90%, and those who have not passed the certification Of small-scale wire and cable manufacturers, the product qualification rate is even less than 30%. According to the survey report issued by the quality inspection agency, the overall pass rate of the wires and cables sold by various franchised stores on the market is about 70%. For those smaller hardware stores, the pass rate of the wires and cables sold by them is about 70%. It's not even 10%. The quality of domestic wires and cables is worrying.

　　Detection method

　　According to the relevant regulations of national standards, the testing items of wire and cable mainly include the testing of electrical performance and mechanical performance. The electrical performance testing mainly includes DC resistance testing, insulation resistance testing and power frequency withstand voltage testing.

　　(1) DC resistance detection

　　There is a clear stipulation in the relevant national standards: the DC resistance of the wire and cable must be based on the conductor resistance per kilometer as a benchmark for comparison, and the measured DC resistance data of the wire and cable must first be converted into a value per kilometer at a temperature of 20°C. DC resistance value. After converting the measured DC resistance value to the DC resistance value at 20℃, if the value is less than the specified standard value, then the wire and cable sample is a qualified product, otherwise it is a substandard product.

　　At present, the relevant domestic departments usually adopt two methods: the bridge method and the current method to determine the DC resistance of wires and cables. The measurement range of the electric bridge method is relatively narrow, which can be divided into single-arm bridge method and double-arm bridge method. When the resistance value of the wire and cable is about 1 or more, the single-arm bridge method is used; when the resistance value of the wire and cable is less than 1, then The double-arm bridge method is adopted. The current method is also called the micro-ohmmeter method. Its principle is to use a constant current source to output different constant currents according to the resistance value of the wire and cable, and then accurately measure the voltage at both ends of the wire and cable under test. The measured data is in accordance with Ohm's law The calculation can get the DC resistance of the measured wire and cable. The current method can output different currents, so its measurement range is relatively wide.

　　 (2) Insulation resistance detection

　　The measured value of the insulation resistance of the wire and cable must be converted into the insulation resistance value per kilometer. The difference from the DC resistance is that the insulation resistance value is inversely proportional to the length of the wire and cable; the measurement voltage of the insulation resistance of the low-voltage wire and cable is 100V. , 250V, 500V and 1000V, of which the detection voltage of 100V and 500V is widely used in quality inspection departments; the length of the measured wire and cable is not clearly specified, but for the convenience of measurement and calculation, 10m is generally used for measurement. The charging time before measurement is generally 1 minute.

　　Wire and cable insulation resistance detection generally adopts the voltage current method, also known as the high resistance meter method. Some wires and cables have a metal protective sheath, which has a certain shielding function. For this kind of wire and cable insulation resistance measurement, most of the insulation resistance between the conductor and the metal sheath or the shielding layer or the armor layer is measured; for the non-metal sheathing When measuring the insulation resistance of the wire and cable, the measured wire and cable must be immersed in water first, and then the insulation resistance between the conductor and the water must be measured, and the tested sample must be kept compatible with the water temperature during testing.