Wires and cables are important products related to personal and property safety. Low-quality wires and cables not only consume a lot of limited energy in the country, but also pose a threat to the safety of people's lives and property. Shenzhen is an important production base of wire and cable in China. After years of supervision by the Municipal Quality Supervision department, the quality of wire and cable products has been at a higher level than that of similar products in the whole country. However, a small number of enterprises are still pursuing profitable profits in order to reduce costs and produce low-quality products, which leads to the low quality of wire and cable products. In order to further improve the quality level of wire and cable products and enhance the competitiveness of wire and cable products in our city, in the second quarter of this year, the Municipal Quality Supervision Bureau organized a spot check on the quality of wire and cable products in the whole city. 44 batches of products were sampled, 28 batches were qualified, the qualified rate was 63.6%, and 16 batches were unqualified, the unqualified rate was 36.4%. At the same time, the test results show that the qualified rate of resistance items of conductors of wires and cables is higher, while the quality level of structural dimensions or mechanical properties of polyvinyl chloride (PVC) or rubber and sheath needs to be improved.
In accordance with the relevant national standards, the spot checks were carried out on conductor resistance, insulation thickness, insulation thinnest point thickness, and pre-aging tensile strength, etc., which are related to personal safety. In this spot check, the quality of wire and cable products in our city has the following characteristics:
The qualified rate of conductor resistance is higher. Copper conductor is an important part of wire and cable, and conductor resistance is an important index to measure the current carrying capacity of wire. The relevant regulations of the state clearly point out that electrolytic copper should be used in copper wires and cables. Of the 44 batches of samples sampled by production enterprises, 40 batches of conductor resistance are qualified, the qualified rate is 90.9%. Four unqualified samples were analyzed by experts. The reasons for the unqualified samples were the reduction of cross-section area and the use of inferior copper. Unqualified conductor resistance will cause serious heating of wire and cable in use and accelerate insulation aging, which is a major fire hazard in fire accidents.
The structural dimensions or mechanical properties of polyvinyl chloride (PVC) or rubber and sheath need to be improved. The insulating and sheathing layers of wires and cables are used to prevent electric shock and to protect copper conductors from corrosion and damage. National standards stipulate that polyvinyl chloride (PVC) or rubber and sheath should have certain thickness and mechanical properties (tensile strength and elongation at break). Among the samples sampled by this manufacturer, 10 batches of samples of polyvinyl chloride (PVC) or rubber and sheath were unqualified in structural dimensions or mechanical properties, with the unqualified rate of nearly 23%. The main reasons for this project's disqualification are as follows: firstly, the production of recycled materials is used to reduce the cost; the insulating materials used in wires and cables should meet the requirements of APS plastics of the national standard, and the insulating layer originally used to prevent leakage and ensure safety. If the wire made of recycled plastics or materials containing high impurities is used, its tensile strength and elongation at break are not found. The method meets the standard requirement. Insulator breakage is easy to occur during installation, which makes live conductor bare. Second, the technical ability is insufficient and the process control is not good. Some wire and cable factories have obsolete production equipment and uneven thickness of insulating layer. With the passage of time or sunshine and rain, insulators break and expose conductors. It is very vulnerable to electric shock, resulting in serious consequences of short circuit, power outage and damage to electrical equipment. In view of the results of the spot check, the Municipal Quality Supervision Bureau has taken different measures according to different situations, and severely punished enterprises that produce inferior cables and wires that do not conform to the national and industrial standards for the protection of human health and personal and property safety, in accordance with the Product Quality Law; ordered enterprises that produce unqualified cables and wires to rectify within a time limit; and rectified unqualified cables after rectification. To arrange follow-up supervision and spot checks, and to request relevant departments to revoke their 3C certificates for wire and cable manufacturers whose results are not up to standard twice in a row; to convene a city-wide Conference on the quality control of wire and cable products, and to strengthen the technical assistance, laws, regulations and related standards of production enterprises. At the same time, the relevant staff of the Municipal Quality Supervision Bureau said that there is knowledge in purchasing wires.
To purchase qualified wires and cables, consumers should pay attention to the following issues:
1. Check the certification marks. All products that have obtained compulsory certification shall be marked with certification marks, namely "CCC" sign, otherwise, they will be unlicensed products.
2. Look at the inspection report. As a product affecting personal and property safety, wires and cables have always been listed as the focus of government supervision and inspection. Regular manufacturers are subject to periodic inspection by supervision departments. Therefore, vendors should be able to provide quality inspection department inspection reports, otherwise, the quality of products will be lack of basis.
3. Insulation and sheath testing. The thickness of insulation and sheath should be uniform and unbiased. Hand induction has obvious tension and elongation. At the same time, the insulation and the surface of the sheath should be printed continuously with the manufacturer's name and product type. The marking interval should be no more than 200 mm for insulation and no more than 500 mm for sheath.
4. Observe the finish and color of the thread. The copper conductors of wires and cables are annealed copper wires plated or not plated. The aluminum conductors are aluminium or aluminium alloy wires with smooth surface, light purple copper conductors and silver-white aluminium conductors. Otherwise, the conductors are likely to be mixed with other impurities, resulting in a decrease in conductivity.
5. Measuring DC resistance. In order to ensure the quality of the wires and cables purchased is qualified, the DC resistance can be measured from 3 to 5 meters of the products to the inspection institution.
6. Measure length. The national standard clearly stipulates the length of wire and cable delivery, the length of coiling should be 100 m, the length of coiling should be more than 100 m. Consumers can measure the length according to the label marking. The standard stipulates that the length error should not exceed 0.5% of the total length. If it does not reach the lower limit of the standard, it will be unqualified.
