Cable joint is also called cable head. After the cable is laid, in order to make it a continuous line, all the lines must be connected as a whole, and these connection points are called cable joints. The cable joint at the middle part of the cable line is called the middle joint, while the cable joints at both ends of the line are called the terminal heads. Cable connectors are used to lock and fix incoming and outgoing lines, and play a role in waterproof, dustproof and shockproof.
Due to the different operation modes and conditions of cable joints, the different technical level of construction personnel and the uneven quality of cable accessories, the reasons for the failure of cross-linked cable joints are also different. The following is an analysis of the causes of cable joint failure by technicians.
(1) The process of making cable joint is poor.
(1) poor handling of the contact surface of connecting hardware. Due to the influence of production or storage conditions, there are impurities, burrs and oxide layers on the inner wall of the terminal or connecting pipe.
② conductor damage. Cross-linked insulation layer has high strength and is difficult to peel. When the constructors cut the ring, they use an electrician knife to cut the left and right, and sometimes they simply cut the deep marks with a hacksaw ring, which often leads to wire damage due to poor mastery.
③ The core wire is not in place. When connecting conductors, the insulation stripping length requires the hole depth of crimping hardware to be increased by 5 mm. However, due to the nonstandard hole depth of products, the stripping length is not enough, or the gap is formed at the end of the wire due to the series position during crimping, which leads to the increase of contact resistance and calorific value only by the wall thickness of the hardware.
⑵ Insufficient pressure.
In the joint manufacturing process and standard drawing, only the number of pressure pits at each end during cable connection is mentioned, but the crimping area and depth are not detailed. The construction personnel have pressed enough pressure pits as required, but the effect cannot be determined.
The main reasons for insufficient conductor connection pressure are as follows:
① Insufficient pressure of crimping tools. There are many manufacturers of crimping tools, but there is no uniform standard. Some mechanical crimping tools have narrow crimping pits and the upper and lower dies do not match after crimping in place. Others implement foreign standards, which are not suitable for the nominal cross section of domestic conductors.
② The gap between connecting fittings is large. The connection fittings used in most cross-linked cable joints are the terminals and crimping pipes produced by fan-shaped conductors of oil-paper cables. Theoretically speaking, the effective cross-sections of circular and fan-shaped wire cores are the same, but the actual operation shows that there is a great difference in crimping effect between them. Because the conductor of the cross-linked cable is a tightly twisted round core, there is a large gap between the conductor and the inner diameter of the commonly used hardware fittings, and it cannot reach enough compression force after crimping. The contact resistance is inversely proportional to the applied pressure, resulting in an increase in resistance.
