A quality inspection organization has conducted a sampling survey on domestic wires and cables. The results show that the qualified rate of wires and cables in production enterprises that have passed ISO 9000 certification is less than 90%, while the qualified rate of products in small-scale wire and cable production enterprises that have not passed certification is even less than 30%. The quality of wires and AAC Cables in China is worrying.
So, don’t be too busy talking about how cheap the AAAC Cable is. Let’s take a look at the following common testing items?
1. Electrical performance test
It mainly includes conductor DC resistance, insulation resistance, finished product voltage test and insulated wire core voltage test, each of which is very important.
The conductor resistance directly reflects the electrical transmission performance of the cable and directly affects the temperature, service life, voltage drop and operation safety of the cable during power on operation. It mainly examines the material and cross-sectional area of the conductor. If the material of the conductor is poor or the cross-sectional area is seriously insufficient, the DC resistance of the conductor will seriously exceed the standard, This kind of cable laying in the line will increase the loss of current passing through the line, cause the heating of the cable conductor itself, cause the insulation aging and cracking of the coated conductor, cause electric leakage and short circuit of the power supply line, and even cause fire, endangering the safety of personal and property. The standard has strict provisions on the DC resistance of conductors of cables of different specifications, which shall not be greater than the value specified in the standard.
Insulation resistance, finished product voltage test and voltage test between insulated cores all examine the electrical insulation performance of cable insulation layer and sheath layer. Insulation resistance is to detect the resistance of insulating material between two conductors, which shall be large enough to play the role of insulation protection. The voltage test of finished products and the voltage test between insulated cores not only require that the ABC Cable has sufficient insulation capacity, but also that the insulation or sheath material is uniform without impurities, the thickness is uniform enough, and there shall be no invisible trachoma, pinhole, etc. on the surface, otherwise it will cause local breakdown during voltage withstand test.
2. Mechanical property test
It mainly examines 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 core breaking test, insulation core tear test, static bending test, etc. for the finished flexible cable.
Tensile strength before and after aging and elongation at break before and after aging are the most important and basic indicators of cable insulation and sheath materials. It is required that the materials used as cable insulation and sheath should not only have sufficient tensile strength, not 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 shall not seriously affect the tensile strength and elongation of materials, which will directly affect the service life of cables. If the tensile strength and elongation at break are unqualified, it is very easy to break sheath or insulator during cable construction and installation, or in light The sheath and insulation of cables used in thermal environment are easy to become brittle and break, resulting in exposed live conductors and electric shock.
In addition, because the flexible cable is not fixed laying, there are repeated dragging and bending in use. Therefore, the flexible cable standard also stipulates that dynamic bending test, bending test, load core breaking test, insulation core tear test, static bending test, etc. are added to the finished cable, so as to ensure that the cable meets the requirements in practical use. For example, the dynamic bending test mainly examines whether the stranded wire of the flexible conductor is broken to reduce the electrical transmission performance, or pierce the insulation to reduce the electrical performance of the insulation when the flexible cable is subjected to external mechanical tensile and bending stresses; It is a test method for whether the insulation is deformed or cracked under stress to affect the electrical insulation performance of cables.
3. Performance test of insulation and sheath materials
Including thermal weight loss, thermal shock, high-temperature pressure, low-temperature bending, low-temperature tensile, low-temperature impact, flame retardant performance, etc. These are to examine the performance of plastic materials for insulation and sheath.
For example, the thermogravimetric test is to detect the degree of degradation and volatilization of the material after 7 days of high-temperature aging at 80 ℃; Thermal shock test whether the specially wound insulation surface is cracked after high temperature of 150 ℃ for 1H; High temperature pressure test the elastic retention of insulating materials after high temperature re cooling; All low temperature tests generally refer to the change of mechanical properties under the condition of – 15 ℃, which is to detect whether the cable material becomes brittle, easy to crack or easy to break under the low temperature environment.
In addition, the flame retardant performance of the cable is very important. The test to check this performance is the non delayed combustion test, that is, the finished cable installed according to the standard is ignited with a special flame for a certain time, and the cable is burned after the flame goes out. Of course, the less the burned part is, the better, indicating that its flammability is poor, its flame retardant is good, and it is safer.
4. Sign check
The standard requires that the cable package shall be attached with labels or marks indicating product model, specification, standard number, factory name and place of origin.
Specifications include rated voltage, number of cores, nominal section of conductor, etc; The cable surface shall be printed with continuous signs of manufacturer’s name, product model and rated voltage. The spacing of signs shall be ≤ 200mm (insulating surface) or ≤ 500mm (sheath surface). The contents of signs shall be complete, clear and scratch resistant. This requirement is convenient for users to understand the model, specification and voltage grade of cables to prevent wrong laying.
In addition, the color recommended by the standard shall be preferred for the insulated wire core of the wire, especially the Yellow / Green two-color wire core. This kind of wire is generally used in the power line of electrical products. This special two-color wire is specially used for grounding. The Yellow / Green matching standard also has the following provisions: for each 15mm long insulated wire core, one color shall 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 core, that is, the Yellow / green two colors shall be basically balanced.
5. Structural dimension detection
Including the thickness, thinnest thickness and overall dimension of insulation and sheath.
The thickness of insulation and sheath plays an important role in how much voltage the cable can withstand and its mechanical performance. Therefore, for cables of different specifications, the standard has strict provisions on the thickness, which shall not be lower than the specified value of the national standard. The cable insulation thickness is too thin, which will seriously affect the use safety of the cable, and will bring potential safety hazards such as cable breakdown and electric leakage caused by bare conductor. Of course, the thicker the better, which should not affect the installation. Therefore, the standard also sets an overall dimension requirement to limit it.
Appendix: common certification
1. CCC certification
Compulsory certification is a pass to enter the domestic market.
2. CB certification
Electrical products directly related to personal safety that are conducive to the export of products for families, offices, workshops and similar places. Such products are subject to compulsory certification in some countries, that is, they are allowed to be exported to the country and sold in the market of the country after obtaining the certification certificate of the country. Even in countries without compulsory certification, consumers are willing to buy certified products with certification marks for their own safety.
3. CE certification
It is a pass for products to enter the markets of EU and European Free Trade Area countries. Products certified with CE mark will reduce the risk of sales in the European market:
1) The risk of being detained and investigated by the customs;
2) Risks investigated and dealt with by market supervision institutions;
3) Risk of peer allegations for competitive purposes.
4. UL certification
In the U.S. market, consumers and buyers are more willing to buy products with UL certification marks.