In the power engineering installation, the cable terminal head and the intermediate joint are important electrical equipment components in the transmission and transformation cable line. Its function is to disperse the electric field at the shielded and cut-off position of the cable terminal, and protect the cable from being broken down. Internal and external insulation and waterproofing. In the cable line, more than 60% of the accidents are caused by the accessories, so the quality of the joint accessories is very important for the safety and reliability of the entire power transmission and transformation. Then, what are the points and matters to be aware of when installing wire and cable joints?
1, the connection of the conductor
Conductor connections require low electrical resistance and sufficient mechanical strength, and sharp corners cannot occur at the joints. Medium and low voltage cable conductor connections are commonly used for crimping. Crimp should be noted:
(1) selecting a conductor connecting tube of suitable electrical conductivity and mechanical strength;
(2) The inner diameter of the crimping tube and the outer diameter of the connected core are taken to be 0.8 to 1.4 mm;
(3) The resistance of the joint after crimping shall not be greater than 1.2 times that of the conductor of equal section, and the tensile strength of the copper conductor joint shall not be less than 60N/mm2;
(4) Before the crimping, the outer surface of the conductor and the inner surface of the connecting tube are coated with a conductive adhesive, and the oxide film is broken by a wire brush;
(5) The connecting tube, the sharp corners on the core conductor, the burrs, etc., smoothed with a file or sandpaper. In addition to the conduit itself, we feature a wide selection of accessories and fittings including mounting brackets, connectors, clamps, junction boxes, couplings, screw connectors and EMT-to-flexible combination couplings. Repair and maintenance equipment is also available from leading brands like American Polywater, including duct sealant, adhesive, repair kits and antifreeze gel for extreme cold weather conditions. For cutting conduit up to 3/8” in diameter, an armored cable cutter will do the trick.
2, the inner semiconductor shielding treatment
Where the cable body has an inner shielding layer, the inner shielding layer of the joint of the crimping tube conductor portion must be restored when the joint is made, and a part of the inner semiconductor shield of the cable is left so that the inner shields of the connecting head on the connecting tube can communicate with each other. The continuity of the inner semiconductor is ensured so that the field strength at the joint is evenly distributed.
3. Processing of external semiconductor shielding
The outer semiconductor shield is a semi-conductive material that acts as a uniform electric field on the outside of the cable and the joint insulation. Like the inner semiconductor shield, it plays an important role in the cable and the joint. The outer semiconductor port must be neat and uniform and requires a smooth transition from the insulation, and the semiconductor winding of the joint is connected to the external semiconductor shield of the cable.
4. Sealing and mechanical protection of joints
The sealing and mechanical protection of the joint is a guarantee for the safe and reliable operation of the joint. Moisture and moisture should be prevented from penetrating into the joint. In addition, joint protection grooves or cement protection boxes should be installed at the joints.
5, cable reaction force cone processing
During the construction, the shape and the correct response force cone are equal. The potential distribution on the whole cone surface is equal. When making the cross-linked cable reaction cone, the special cutting tool is generally used, or the micro-fire can be slightly heated, and the fast knife is used. After cutting, after basic molding, it is then scraped with 2mm thick glass, and finally sanded from coarse to fine with sandpaper until smooth.
6, metal shielding and grounding treatment
The role of the metal shield in the cable and the joint is mainly used to conduct the cable fault short-circuit current, and the electromagnetic interference of the shielded electromagnetic field to the adjacent communication equipment. In the operating state, the metal shield is at zero potential in a good grounding state, after the cable fails It has the ability to conduct short-circuit currents in a very short time. The grounding wire should be soldered reliably. The metal shielding and armoring tape on the cable body of the two ends of the box are firmly welded, and the grounding of the terminal head should be reliable.
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