Wire and cable are materials used for power, electrical, and related transmission purposes. There is no strict boundary between “wire” and “cable”. Generally, products with a small number of cores, a small diameter, and a simple structure are called wires; those without insulation are called bare wires, and others are called cables. The conductor cross-sectional area of the larger (greater than 6 square millimeters) is called a large cable, and the smaller (less than or equal to 6 square millimeters) is called a small wire, also known as cloth wire.
Wire and cable specifications and elements of construction and installation
First, the wire and cable model specification selection:
1. The choice of wire and cable models
Piece of wire and cable, to consider the use, laying conditions, and safety;
For example, according to the different uses, you can choose power cables, overhead insulated cables, control cables, etc.
According to the different laying conditions, you can choose the general plastic insulated cable, steel tape armored cable, steel wire armored cable, anti-corrosion cable, etc.;
According to the safety requirements, one can choose not to use flame retardant cable, flame retardant cable, halogen-free flame retardant cable, fire-resistant cable, and so on.
2. The choice of wire and cable specifications
Determine the use of wire and cable specifications (conductor cross-section), generally should consider the heat, voltage loss, economic current density, mechanical strength, and other selection conditions. According to experience, low-voltage power lines because of their load current, generally first according to the heat conditions to select and then calculate the voltage loss and mechanical strength; low-voltage lighting lines, because of their high voltage level requirements, can be first according to the conditions of the permissible voltage loss to select the cross-section, and then calculate the needs of the heat and mechanical strength; high-voltage lines, it is the first to choose the cross-section according to the economic current density, and then calculate the conditions of the heat and the permissible voltage loss And high-voltage overhead lines. Still, its mechanical strength should be calculated.
Second, the transportation and storage of wire and cable
1. The transportation is strictly prohibited from throwing down the cable or cable tray with cable, especially at lower temperatures (generally about 5 ℃ and below). Throwing and dropping the line will likely lead to insulation and sheath cracking.
2. As far as possible, to avoid storing cables in the open air in a bare way, the cable tray is not allowed to be placed flat; it should be placed upright.
3. When lifting the package, it is strictly prohibited to lift several disks at the same time. In vehicles, ships, and other means of transportation, cable trays should be fixed in a suitable way to prevent each other from colliding or tipping to avoid mechanical damage to the cable.
4. The cable is strictly prohibited from acid, alkali, and mineral oil contact to be stored in isolation from these corrosive substances. Storage of lines in the warehouse shall not damage the insulation and corrosion of the metal in the presence of harmful gases.
5. The cable in the storage period should be rolled regularly (3 months in summer; other seasons can be extended as appropriate). Rolling will be stored down the side of the disk rolled over towards the top to avoid the bottom side of the moisture decay. Storage should always pay attention to whether the cable head is intact.
6, cable storage period to the product factory period as a limit, generally should not exceed one and a half years, the longest not more than two years.
Third, the installation and construction of wire and cable
Wire and cable laying and installation design and construction should be carried out by relevant regulations and the use of necessary cable accessories (terminals and connectors). The operation quality, safety, and reliability of the power supply system are related to the quality of the wire and cable itself and the construction quality of the cable accessories and lines.
The statistical analysis of the line failure due to construction, installation con, section, and other factors caused by the loss is often much more likely than the failure caused by defects in the wire and cable.
Should pay attention to the following aspects of the problem:
1. Qualified professional units or professionals should perform cable laying and installation. If it does not meet the requirements of the relevant norms and regulations of construction and installation, it may lead to the cable system not operating normally.
2, workforce laying cables should be unified command control rhythm; every 1.5 ~ 3 meters, a person carries the line on the shoulder, puts a side pull, and slowly casts.
3, mechanical cable application, the general use of a special cable laying machine equipped with the necessary traction tools, traction appropriate size, and control uniformity to not damage the line.
4. Casting cable before to check the appearance of the line and the head is intact, casting attention to the direction of rotation of the cable tray. Do not flatten or scrape the cable sheath. Do not straighten the cable in the way of wrestling in cold winter temperatures to avoid the insulation; the sheath is injured and cracked.
5. Laying the cable bending radius should exceed the specified value. Before and after the installation of the cable, applying a 1000V megohmmeter to measure the insulation resistance between the conductors of the line is standard and according to the specifications of the cable type, length, and ambient temperature of the measurement results to make appropriate corrections, small specifications (10m ㎡ below the solid conductor) cable should also be measured whether the conductor is on and off.
6, a cable such as direct burial, pay attention to soil conditions, general buildings under the line buried depth of not less than 0.3 meters, softer or more complex surrounding environment, such as arable land, building construction sites or roads, etc., there should be a certain depth of burial (0.7 ~ 1 m) to prevent accidental damage to the direct buried cable, if necessary, should be erected obvious warning signs.