Four principles for choosing overhead cables

In the selection of overhead cable, overhead cable, in general, should pay attention to the models, and specifications (conductor cross-section) of choice.

Overhead cable type selection

Selection of overhead cable, consider the use, laying conditions, and safety, for example,

Depending on the application, the choice of power cables, overhead insulated cables, control cables;

Depending on the laying conditions, the choice of general plastic insulated cables, steel armored cable, steel wire armored cable, cable, and other anti-corrosion;

According to security requirements, you can choose retardant cables, fire-retardant cables, flame retardant cables, and fire-resistant cables.

Overhead cable size selection

Determine the use of overhead cable specifications (conductor cross-section), the general should consider heat, voltage loss, economic current density, mechanical strength, etc. selection criteria. According to experience, in low-voltage power lines because the load current is large, it is generally to press the heating conditions are selected cross-section, and then check the voltage loss and mechanical strength; low voltage lighting lines because of their high-level requirements, press the allowable voltage loss condition Select profile, then checking fever conditions and mechanical strength; high-voltage lines, then press the economic current density select section, and then checking their condition and allow the voltage loss fever; and high voltage overhead lines, but also checking its mechanical strength. If the user does not have experience, you should consult the relevant specialized units or persons.

Explanation:

1. The same specification aluminum wire carrying capacity of approximately 0.7 times the copper core, the choice of aluminum wire large a size comparable copper wire, XLPE insulation can choose a file size small, the fire-resistant overhead cable should choose the larger size.

2. this table is calculated based on a three-phase capacity 380V, Cosφ = 0.85 as the base, if the single-phase 220V, Cosφ = 0.85, capacity should × 1/3.

3. When the ambient temperature is high or the methods used for surface, with its safe current carrying capacity will drop, and you should choose a larger size; when the starter motor is used frequently, should be used 2 ~ 3 specifications.

4. This form of PVC insulated wire laid by a single overhead calculated, if it is wearing a tube or a plurality of laying, should be used 2 ~ 3 specifications.

5 The above data is for reference only, the final design and determine the cable type and size should refer to the relevant professional information or electrician manual.

Overhead cable transport and storage

1. Prohibited transportation of dropped cable or equipped with cable reels from a height, especially at lower temperatures (typically about 5 ℃ and below), throw, throw cable will likely result in insulation, and sheath cracking.

2. Possible, avoid storing in an open way to the exposed cables, the cable tray does not allow flat.

3. Lifting packages, the prohibited several dishes at the same time lifting. In vehicles, ships, and other means of transport, the cable tray uses appropriate methods to be fixed, to prevent collision or falls, and to prevent mechanical damage to cables to each other.

4. Cable is strictly prohibited from contact with acids, bases, and mineral oils, to be stored with corrosive substances isolated. There shall be no storage warehouse destroyed cable insulation and corrosion of metals harmful gases.

5. Cable during custody should be periodically rolling (summer 3 months, other seasons can be extended as appropriate). When you scroll, the store-down rim rolls upward, to avoid the bottom surface of damp rot. When storing should always pay attention to the cable head intact.

6. Cable shelf-life period is limited to the factory, usually not more than a year and a half, no longer than two years.

Installation and construction of the overhead cable

Design and construction of wire and cable laying installation shall be the relevant provisions of GB 50217-94 "Electrical Engineering cable design specifications", etc., and to adopt the necessary cable accessories (terminals and joints). Power Supply System in the quality, safety, and reliability is not only the quality of the wire cable itself but also with the construction quality cable accessories and related lines.

Through statistical analysis of line fault, due to construction, installation and connection and other factors caused the failure is often much greater than the probability of failure caused by faulty wire cable body. Therefore, to correctly use overhead cable and related accessories, in addition to specifications for design and construction, we must also pay attention to the following aspects of the problem:

1. Cable laying installation by a qualified professional unit or professionals does not comply with the relevant norms of construction and installation requirements, it may cause the cable system can not to function properly.

2. Manpower when laying cable, unified command, and control rhythm, every 1.5 to 3 meters cable with one shoulder, side discharge side pull, slowly cast.

3. Mechanical cast cable, generally use a dedicated cable laying machine tools equipped with the necessary traction, traction size appropriate to control uniform, in order to avoid damaging the cable.

4. Cast cable before, to check whether the cable appearance and head are intact, note the direction of rotation of the cable reel when cast, do not crush or scratch the cable sheath, not to low temperature in winter when the best way to school straight cable, in order to avoid insulation, sheath cracking.

5. When laying the cable's bend radius is greater than a predetermined value. Before cable laying installation, the insulation resistance between the rear with 1000V megger cable conductors are normal, and according to the cable model specifications, different length and ambient temperature on the measurement results be properly corrected, the small size (less real 10m㎡ core conductor) cable should measure whether the conductor of.

6. Such as burying cables, paying attention to soil conditions, laying cables under the general building not less than 0.3 meters deep, soft, or the surrounding environment has become more complex, such as arable land, construction sites or roads, there should be some buried depth (0.7 to 1 meter) to prevent accidental damage to buried cables, if necessary erect signs.