1. Electrical performance testing
The main tests include conductor DC resistance, insulation resistance, finished product voltage test, and voltage test between insulated cores. Each test is crucial. Conductor resistance directly reflects the electrical transmission performance of the cable, directly affecting its temperature, lifespan, voltage drop, and operational safety during energized operation. It primarily examines the conductor material and cross-sectional area. If the conductor material is poor or the cross-sectional area is severely insufficient, the conductor DC resistance will significantly exceed the standard. Laying such a cable in a power line will increase current loss as it flows through the line, causing the cable conductor itself to heat up, leading to aging and cracking of the insulation covering the conductor, resulting in leakage, short circuits, and even fires, endangering personal and property safety. The standard has strict regulations on the conductor DC resistance values for different cable specifications, which must not exceed the values specified in the standard.
Insulation resistance, finished product voltage test, and insulated core voltage test all examine the electrical insulation performance of the cable's insulation and sheath layers. Insulation resistance measures the resistance of the insulating material between two conductors; it should be sufficiently high to provide insulation protection. The finished product voltage test and insulated core voltage test not only require the cable to have sufficient insulation capacity, but also require that the insulation or sheath material be uniform, free of impurities, and of sufficiently uniform thickness. The surface must be free of invisible pinholes or other defects, otherwise, localized breakdown will occur during the withstand voltage test.
2. Mechanical performance testing
The main focus is on examining the tensile strength and elongation at break of the insulating and sheathing plastic materials, both before and after aging. Tests also include flexure, bending, load-induced core breakage, insulation core tearing, and static flexure tests on finished flexible cables. Tensile strength before and after aging, and elongation at break before and after aging, are the most important and fundamental indicators for cable insulation and sheathing materials. Materials used for cable insulation and sheathing must possess sufficient tensile strength to prevent breakage, while also exhibiting a certain degree of 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, as these will directly affect the service life of the cable. If the tensile strength and elongation at break are not up to standard, the sheath or insulation is very likely to break during the construction and installation of the cable. Alternatively, the sheath and insulation of cables used in light and heat environments are prone to become brittle and break, resulting in the exposure of live conductors and the risk of electric shock.
Furthermore, since flexible cables are not fixedly laid, they are subject to repeated dragging and bending during use. Therefore, the standard for flexible cables specifies additional tests such as dynamic flexure test, bending test, load-induced core breakage test, insulation core tear test, and static flexure test on the finished cable to ensure that the cable meets the requirements in actual use. For example, the dynamic flexure test mainly assesses whether the stranded wires of the flexible conductor break when the flexible cable is subjected to external mechanical tension and bending stress, thus reducing the electrical transmission performance, or whether the insulation is punctured, thus reducing the electrical insulation performance; it is also a test method to assess whether the insulation deforms or cracks under stress, thus affecting the electrical insulation performance of the cable.
3. Performance testing of insulation and sheathing materials
These tests include thermal weight loss, thermal shock, high-temperature pressure, low-temperature bending, low-temperature tensile testing, low-temperature impact testing, and flame retardancy. These tests examine the performance of the plastic materials used for insulation and sheathing. For example, the thermal weight loss test measures the degree of material degradation and volatilization after 7 days of aging at 80°C; the thermal shock test checks for cracking on the surface of specially wound insulation after 1 hour at 150°C; the high-temperature pressure test measures the degree to which the insulation material retains its elasticity after high-temperature cooling; and all low-temperature tests generally refer to changes in mechanical properties at -15°C, detecting whether the cable material becomes brittle, prone to cracking, or easily breaks in low-temperature environments. Furthermore, the flame retardancy of cables is very important. The test for this performance is the non-flame-retardant test, which involves igniting a standard-installed finished cable with a special flame for a certain period. After the flame extinguishes itself, the extent of burning is checked. The less burned, the better, indicating poor flammability, good flame retardancy, and greater safety.
4. Marking Inspection
The standard requires that cable packaging should be labeled or marked with the product model, specifications, standard number, manufacturer's name, and place of origin. Specifications include rated voltage, number of cores, and nominal conductor cross-section. The cable surface should be printed with continuous markings of the manufacturer's name, product model, and rated voltage. The marking spacing should be ≤200mm (insulation surface) or ≤500mm (sheath surface). The markings should be complete, clear, and resistant to abrasion. This requirement is to help users understand the cable's model, specifications, and voltage rating to prevent incorrect installation.
In addition, the standard recommended colors should be given priority for the insulation cores of electrical wires. It is worth mentioning the yellow/green bicolor cores. This type of wire is generally used in the power cords of electrical products. This special bicolor wire is dedicated to grounding. The standard for yellow/green matching also has the following provisions: for each bicolor insulated core of a length of about 100 mm, one color should cover at least 30% and no more than 70% of the surface of the insulated core, while the other color should cover the rest of the insulated core. That is, the yellow/green bicolor should be basically balanced.
5. Structural Dimension Inspection
This includes the thickness, minimum thickness, and overall dimensions of the insulation and sheath. The thickness of the insulation and sheath plays a crucial role in the voltage resistance of the cable and its mechanical properties. Therefore, standards have strict regulations on the thickness of cables of different specifications, requiring it not to be lower than the national standard values. Insulation that is too thin will seriously affect the safety of the cable, leading to safety hazards such as cable breakdown and leakage caused by exposed conductors. However, thicker is not always better; it should not hinder installation. Therefore, the standard also includes dimensional requirements to limit this.
Common certification marks
1. CCC certification is a mandatory certification and a passport to enter the domestic market.
2. CB certification is beneficial for exporting electrical products used in homes, offices, workshops, and similar locations that directly involve personal safety. In some countries, these products are subject to mandatory certification; that is, only after obtaining a certificate of conformity from that country are they allowed to be exported and sold in that market. Even in countries without mandatory certification, consumers are willing to buy certified products bearing the certification mark for their own safety.
3. CE certification
It serves as a passport for products entering the markets of the EU and the European Free Trade Area. Products that have obtained certification and bear the CE mark will reduce the risks of selling in the European market.
1) Risk of being detained and investigated by customs;
2) The risk of being investigated and punished by market supervision authorities;
3) Risk of accusations from competitors for competitive purposes.
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