(1) DC resistance detection. The relevant national standards have clear provisions: the DC resistance of the wire and cable must be used as the reference for comparison of the conductor resistance per kilometer, and the DC resistance data of the measured wire and cable must first be converted into the DC resistance value per kilometer at a temperature of 20 ° C. After converting the measured DC resistance value into the DC resistance value under the condition of 20℃, if the value is less than the specified standard value, then the wire and cable sample is a qualified product, and otherwise it is an unqualified product. At present, the relevant departments in China usually use bridge method and current method to measure the DC resistance of wire and cable. The measuring range of the bridge method is relatively narrow, 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, the double-arm bridge method is used.

Current method is also known as the micrometer method, its principle is based on the size of the resistance value of the wire and cable, the use of constant current source output different constant current, and then accurately measure the voltage at both ends of the measured wire and cable, the measured data can be calculated according to Ohm's law to obtain the DC resistance of the measured wire and cable. Current method can output different currents, so its measurement range is relatively wide.



(2) Insulation resistance detection.

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

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