National standard cable protection test need to do what test?

1. Check the cable resistance

The main conductor DC resistance, insulation resistance, finished voltage test and voltage test between insulated wire cores, each is very important, conductor resistance directly reflects the electrical transmission performance of the cable, directly affects the temperature, life, voltage drop, and operation safety of the cable in energized operation, it mainly examines the material and cross-sectional area of the conductor, if the material of the conductor is not good or the cross-sectional area is seriously insufficient. This kind of cable laid in the line will increase the loss when the current passes through the line, causing the cable conductor itself to heat, causing the insulation aging and cracking of the covered conductor, resulting in power supply line leakage, short circuit, and even cause fire, endangering the safety of people and property. The standard has strict provisions on the conductor direct current resistance of different specifications of cables, which shall not be greater than the value specified in the standard.

The insulation resistance, the finished product voltage test and the voltage test between the insulated wires are all examining the electrical insulation performance of the cable insulation layer and the sheath layer. The insulation resistance is the resistance of the insulating material between the two conductors, which should be large enough to play the role of insulation protection. The finished voltage test and the voltage test between the insulated wires not only require the cable to have sufficient insulation capacity, but also require the insulation or sheath material to be uniform without impurities, the thickness is uniform enough, and the surface can not have invisible trachoma, pinholes, etc., otherwise it will cause local breakdown during the voltage test.

2. Cable mechanical performance test

It is mainly to examine the tensile strength and elongation at break of insulation and sheath plastic materials, including before and after aging, as well as the bending test, bending test, load breaking core test, insulation core tearing test, static bending test and so on for finished flexible cables. The tensile strength before and after aging, and the elongation at break before and after aging are very important indicators of cable insulation and sheathing materials, which are required to be used as cable insulation and sheathing materials, which should have sufficient tensile strength and not be easy to break, but also have certain flexibility.

Aging refers to the ability of insulation and sheath materials to maintain their original properties under high temperature conditions, aging should not seriously affect the tensile strength and elongation of the material, which will directly affect the service life of the cable, if the tensile strength and elongation at break are not qualified, the construction and installation of the cable is very easy to appear sheath or insulator fracture. Or the sheath and insulation of the cable used in the light and thermal environment are easy to become brittle and break, resulting in the live conductor exposed and the risk of electric shock.

In addition, because the flexible cable is not fixed laying, there are repeated dragging, bending and other situations in use, so the flexible cable standard also stipulates that dynamic bending test, bending test, load broken core test, insulated wire core tear test, static bending test, etc. are added to the finished cable to ensure that this cable meets the requirements in actual use. For example, the dynamic flexure test mainly examines whether the stranded wire of the flexible conductor breaks and reduces the electrical transmission performance when the flexible cable is subjected to external mechanical tensile and bending stresses, or punctures the insulation and reduces the electrical insulation performance; Insulation under stress is a test method of whether deformation or cracking will affect the electrical insulation performance of the cable.

3. Cable insulation and sheath material performance test

Including thermal weight loss, thermal shock, high temperature pressure, low temperature bending, low temperature tensile, low temperature impact, flame retardant performance and so on. These are to examine the performance of insulation and sheath plastic materials, such as thermogravimetric test is to detect the degree of material degradation and volatilization after 7 days of high temperature aging at 80 ° C; Thermal shock test whether the insulation surface is cracked after special winding at 150℃ for 1h; High temperature pressure test insulation material after high temperature and then cooling its elasticity; All low-temperature tests generally refer to the change in its mechanical properties under the condition of -15 ° C, which is to detect whether the cable material becomes brittle, easy to crack or easy to break at low temperatures. In addition, the flame retardant performance of the cable is very important, the test of the performance is not delayed fire test, that is, the finished cable installed according to the standard is lit with a special flame for a certain time, to check the cable is burned after the flame is extinguished by itself, of course, the less the part that is burned the better, indicating that its combustion is poor, flame retardant is good, the safer

4. Check cable labels

The standard requires that labels or signs indicating product model, specification, standard number, manufacturer name and origin should be attached to the cable packaging, including the rated voltage, number of cores and nominal section of the conductor; The cable surface should be printed with the manufacturer's name, product model and rated voltage of the continuous mark, mark spacing requirements ≤200mm(insulation surface) or ≤500mm (sheath surface), the content of the mark should be complete, clear, rub resistant, this requirement is convenient for users to understand the cable model specifications and voltage level, to prevent laying errors.

In addition, the wire insulation core should be preferred the color recommended by the standard, especially the yellow/green two-color core, this line is generally used in the power line of electrical products, this special two-color line is dedicated to grounding, for the yellow/green collocation standard also has the following provisions: That is, for each length of the two-color insulated wire core, one of the colors should cover at least 30% of the surface of the insulated wire core, and not more than 70%, while the other color covers the rest of the insulated wire core, that is, the yellow/green two-color should be basically balanced.

5. Check the cable structure dimensions

Including insulation and sheath thickness, Z thin thickness, shape size, etc. The thickness of the insulation and sheath plays a very important role in how much strength the cable can withstand the voltage, as well as its mechanical properties, so for different specifications of the cable, the standard has strict regulations on the thickness, requiring that it should not be lower than the specified value of the national standard. Cable insulation thickness is too thin will seriously affect the use of the cable safety, will bring cable breakdown, conductor exposure caused by leakage and other security risks, of course, not the thicker the better, should not affect the installation, so the standard and set a dimension requirements to limit this.

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