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What tests need to be done for commonly used wires and cables?

Update:2020-12-21
Abstract:

1. Electrical function test There are mainly conductor […]

1. Electrical function test
There are mainly conductor DC resistance, insulation resistance, product voltage experiment and insulated wire-core voltage experiment, each of which is very important. The conductor resistance directly reflects the electrical transmission function of the cable and directly affects the temperature, life and voltage of the cable during 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, the DC resistance of the conductor will be seriously exceeded. This kind of cable laying in the line will increase the current on the line. The loss during passing will cause the cable conductor itself to heat up, cause the insulation of the coated conductor to age and crack, cause the power supply line to leak, short-circuit, and even cause fires, endangering personal and property safety. The specification has strict rules on the conductor DC resistance value of cables of different specifications, which shall not be greater than the value of the specification rules.

Insulation resistance, product voltage experiment and insulated wire-core voltage experiment all examine the electrical insulation function of the cable insulation layer and sheath layer. Insulation resistance is the resistance of the insulation material between two conductors. It should meet the requirements To insulation protection. The product voltage test and the inter-core voltage test of the insulated wire not only require the cable to have satisfactory insulation capacity, but also require the insulation or sheath material to be uniform, free of impurities, and uniform in thickness. There should be no invisible trachoma, pinholes, etc. on the surface, otherwise it will cause Partial breakdown during withstand voltage test.

2. Mechanical function testing
The main purpose is to examine the tensile strength and elongation of insulation and sheath plastic materials, including before and after aging, as well as the bending test, bending test, load breaking test, insulated core tearing test, Static torsion experiment, etc. The tensile strength before and after aging, and the elongation at break before and after aging are the most important and basic targets of cable insulation and sheath materials. It is required to be used as cable insulation and sheath materials. It must have satisfactory tensile strength and not easy to pull. It must have a certain degree of flexibility. Aging refers to the ability of insulation and sheath materials to maintain their original functions under high temperature conditions. Aging should not seriously affect the tensile strength and elongation of the materials, which will directly affect The service life of the cable, if the tensile strength and cracking elongation are unqualified, the sheath or insulator will be easily cracked during the construction and installation of the cable, or the sheath and insulation of the cable used in the light or heat environment will easily change It is brittle and cracked, causing the live conductor to be exposed, causing the risk of electric shock.

Since other flexible cables are not fixedly laid, there are repeated pulling and bending in use, so there are other rules for the flexible cable specifications. Dynamic bending experiments, bending experiments, load-breaking experiments, and insulation are added to the product cables. Core tear test, static bending test, etc., to ensure that this cable meets the requirements in actual use. For example, the dynamic torsion test mainly examines whether the twisted wires of the flexible conductor crack and reduce the electrical transmission function when the flexible cable is subjected to external mechanical tension and bending stress, or whether the insulation is pierced to reduce the electrical function of the insulation; Being under stress is an experimental method to determine whether the electrical insulation function of the cable is affected by deformation or cracking.

3. Insulation and sheath data function experiment
Including thermal weight loss, thermal shock, high temperature pressure, low temperature bending, low temperature stretching, low temperature impact, flame retardant functions, etc. These are to investigate the function of insulation and sheathing plastic materials. For example, the thermal weight loss test is to detect the degree of degradation and volatilization of the materials after 7 days of high temperature aging at 80°C; the thermal shock test is subjected to a special roll after a high temperature of 150°C for 1 hour. Whether the insulation surface of the winding is cracked; the high temperature pressure detects the elasticity of the insulation material after passing the high temperature and then cooling; all the low temperature experiments generally refer to the change of the mechanical function under the condition of -15 ℃, which is the detection of the cable data Whether it becomes brittle, easy to crack or break under low temperature environment.

The flame-retardant function of other cables is very important. The experiment to investigate this function is a non-flame test, that is, the product cable installed according to the specification is ignited with a special flame for a certain period of time, and the cable is checked after the flame goes out by itself. In the case of burnt, of course, the less burnt part is, the better, which clarifies that the burnability is poor, the flame retardancy is good, and the safer.

4. Logo inspection
The specification requires that the cable packaging should be accompanied by a label or logo indicating the product type, specification, specification number, manufacturer name and place of origin. The specifications include additional voltage, core number and nominal conductor cross-section, etc.; the cable surface should be printed with the manufacturer’s name and product type For continuous marks with additional voltage, the mark distance is required to be ≤200mm (insulated surface) or ≤500mm (sheath surface). The content of the mark should be complete, clear and scratch-resistant. This requirement is to facilitate users to understand the type, specification and voltage level of the cable. To prevent laying errors. In addition, the color of the wire insulation core should be the color recommended by the specification, especially the yellow/green two-color core. This kind of wire is generally used in the power cord of electrical products. This special two-color wire is dedicated to grounding. The yellow/green collocation specification also has the following rules: that is, for each 15mm length of 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%, and the other color should cover the insulated wire The rest of the core, the yellow/green color, should be basically balanced.

5. Structure size detection
Including the thickness, thinnest thickness, overall dimensions of the insulation and sheath. The thickness of the insulation and sheath plays an important role in the strength of the cable and its mechanical function. Therefore, for cables of different specifications, the specifications have strict rules on the thickness, and the requirements must not be lower than that of the country. Normative rule value. If the insulation thickness of the cable is too thin, it will seriously affect the safety of the cable. It will bring safety hazards such as cable breakdown and exposed conductors, causing electric leakage. Of course, it is not the thicker the better. It should not affect the installation. Therefore, the specification sets a requirement for external dimensions. Limit this.

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