We all know that the quality of products, good or bad, its first feature is reflected from the appearance of the product quality, regardless of which product, or semi-finished products, in the production must pay attention to the appearance of quality, strict control and inspection of its implementation. Sheath is the appearance of the cable, its appearance requirements are smooth round, gloss evenly, not eccentric (not exceeding the specified deviation), no mechanical damage, compressed, no visual visible sundries, bubbles, sand holes, obvious particles, bamboo-shaped, twist-shaped, and so on.

In addition to meet the above quality requirements, sheath thickness of cable quality also has a certain impact. Sheath thickness below the standard requirements of course unqualified, but the thickness exceeds the standard requirements, but also unqualified. For example: Cable model for ZR-KVVP 4*1.5mm2, measured by the thickness of the average thickness of 1.6mm, such models such as reference gb9330-88 standard requirements, thickness should be 1.2mm.

The reasons for the failure are as follows: 

(1) Reduce service life. After the cable is laid, it will power up for a long time electricity will produce heat, the conductor allowed to work temperature of 70 ℃, PVC long-term use temperature should not exceed 65 ℃, if in summer, working temperature will rise, these temperatures will be distributed through the outer layer, sheath thickness, heat energy is difficult to distribute, will affect cable service life,

Because of the thermal effect of polyvinyl chloride, the insulating layer occurs a series of physical and chemical changes, loss of the original excellent performance, resulting in a marked decline in insulation performance, or even a short-circuit, affecting the normal operation of the unit. 

(2) Material performance defects.

Material performance is not reflected by the thickness, according to the GB8815-2002 standard requirements,

    That one of its indicators is substandard, flame-retardant PVC material, that its oxygen index is less than 30. 

(3) Cable structure problems.

If the conductor, insulating layer, woven density, in accordance with the standard requirements of control, select the appropriate filler to make the round, so how can the sheath squeeze so thick? 

(4) Increase the difficulty of cable laying.

Cable laying now to bridge or pipe-oriented, now many enterprises are in the implementation of cable requirements, small diameter, in the laying process can have gaps, heat energy, to ensure that the cable sheath is not damaged, otherwise, to the construction unit and cable laying bring some difficulties. To sum up, the thickness of the sheath should be in accordance with the standard control, so that both for the enterprise to save resources, reduce material consumption, increase profits, but also to ensure cable quality, create high quality and low price products.