Laying and installation of pre branched cables

1、 Laying and installation of pre branch cable
Prepare for laying and installation according to the requirements of design drawings and be familiar with the laying direction and location of cables.
(1) Formulate construction plan and organize professional construction personnel.
(2) Prepare for installation of tools and equipment.
(3) Verify the abc cable model and specification and packing sequence.
(4) Verify the accessories and assign the installation site of accessories to the construction party.
(5) Place cable tray on the cable release frame.
(6) When the cable is installed vertically, the cable laying frame is lower than the floor, and the cable is lifted by winch or pulley block through the rope. Professional construction personnel shall be required for each floor. As for the terminal, hang the cable on the installed hook
(7) When the cable is installed horizontally, the cable setting out frame shall be set by the professional construction personnel (one person every two meters and the commander) as for the receiving position.


(8) Fix the intermediate part of the main and branch lines of prefabricated branch cables as required.
(9) Connect the main line and branch line with the electrical control device in phase sequence.
(10) After installation, clean the site, measure the insulation resistance of each circuit connected to each phase of prefabricated branch cable.
(11) Fill in the construction record.
2、 Precautions during laying and installation
(1) When laying, it is necessary to use the vertical hoisting as far as possible. When the construction site is restricted or special requirements are required, reverse installation can be used. No matter which setting method, the branch line shall not be released in advance in the process to prevent the branch body from scratching when passing through the hole and avoid being subjected to excessive mechanical external force.
(2) During lifting and hoisting, the cable with a weight of more than 4 times the strength must be selected. After laying, the upper and lower installation and fixing fixture shall be carried out first.
(3) The bending radius of cable shall not be less than 25d during laying and installation.
(4) Metal clamps are not allowed when fixing single core prefabricated branch cables.
(5) When connecting the main line and branch line with the receiving and electric measuring apparatus, the metal clamp must be used and the metal type of the clamp shall be selected correctly.

(6) The spreader must be installed on the load-bearing wall.

A big explanation of high-voltage cables

Power cables have become a necessity in human life and production, and play an important role in many fields and industries, including home appliances, automobiles, houses, engineering, transportation, and so on. The demand for high-voltage power cables has been increasing in recent years, and cable companies have also entered the market.


The main technology for the production of high-voltage cables is CV continuous vulcanization production. This production line converts polymers into high-performance insulating materials and wraps metal conductors to form cables. As far as China’s high-voltage cable market is currently in a state of overcapacity, Chinese cable companies have invested in building a large amount of production capacity, but demand cannot keep up with the substantial expansion of production capacity.


Statistics show that China’s high-voltage power cable production accounted for 40% of the world’s total in 2014. At present, there are more than 185 continuous vulcanization production lines in China that can theoretically produce conductors for high-voltage power cables, accounting for 50% of the global production of high-voltage cable CV continuous vulcanization production lines. Although many of these CV lines are not in production, or have not even obtained relevant approvals, China’s high-voltage cable production capacity still exceeds its demand by three times. Today, the output of high-voltage cables will continue to increase until 2021.
As the traditional high-voltage cable market is saturated with overcapacity and its competition is becoming increasingly fierce, some powerful cable companies have turned to high-voltage submarine cables. This field has higher requirements for technical thresholds. Only a few companies in China have Strong production, and with the construction of wind farm projects in many countries around the world, the demand for high-voltage submarine cables will increase in the future.

The Bare conductor has no sheath, is it safe?

In daily life, many people will see high-voltage power cables in the suburbs. They are often erected in mid-air, but many people may not observe carefully. Many of the high-voltage wires that are erected in the air are bare wires. The so-called bare wires are not insulated. The cable of the skin.


Usually the wires and cables we buy have a layer of insulation. The function of the insulation is to protect the inside of the cable from damage, and to prevent us from getting an electric shock. However, the high-voltage line has no insulation, and the second is a bare wire. Why? What?
The voltage of domestic high-voltage transmission lines is often above 10,000 volts, while China’s unique ultra-high voltage technology has a higher voltage, and the cables used in high-voltage lines are basically bare wires. Generally, lines above 10 kV will be used. .


The reason whyBare conductors are used in high-voltage lines is very simple. If the high-voltage lines are to be insulated for cables, the thickness of the ordinary insulation layer is far from enough. If the insulation layer is to be used, its thickness needs to be increased. , This will make the weight of the cable become very large, will increase the maintenance cost of the later line. Moreover, such a thick insulating layer will also affect the heat dissipation of the cable. The final result of poor heat dissipation is to increase the consumption of electric energy. Therefore, comprehensively considered, the benefits of adding an insulating layer cannot offset the negative effects brought about, so simply don’t need an insulating layer. Attach bare wires directly.
From the design point of view, bare wires are obviously better than cables with insulation, but if you consider their safety issues, will the use of bare wires cause harm to people? In fact, you don’t need to worry. High-voltage lines sound terrible, but the high-voltage lines are difficult for ordinary people to reach. They are all in remote suburbs and are elevated in the air, so ordinary people can hardly touch them.
The operation of the staff also has strict operating specifications in the industry. There are air gaps between the wires and the ground, between the wires and the wires, between the wires and the ground, and between the wires and the tower. Perform accurate calculations and leave a sufficient safety distance.
So generally speaking, it is not very dangerous, but if there are high-voltage lines in the area where you are moving, you should still keep a safe distance.

What is Bare Wire & Bare Conductor ?

Cable products with only conductors without any insulation layer are called “bare wires and bare conductor products”. In order to ensure the current flow along the wire and electrical safety, external insulation suitable for the line voltage must be installed during installation, such as space separation, insulator support, etc. Therefore, this type of product itself does not indicate “use voltage”.

1. Bare single wire
Refers to non-ferrous metal single wires of different materials and sizes, which can be divided into round single wires (copper, aluminum and aluminum alloys cable), flat wires (copper, aluminum and their alloys), single wires with metal plating (tin, silver, nickel) and Bimetallic wires (aluminum-clad steel, copper-clad aluminum, copper-clad steel), etc.
Most of these products are used as materials for the next production of wire and cable products.

2. Bare stranded wire
This is the leading product in this category. Because it is always erected on a pole, it is customarily called an overhead wire. Overhead conductors are not divided into voltage levels. In principle, the same series of conductors can be used from low voltage, medium voltage, high voltage and even ultra high voltage. However, the 330-500kv level has special requirements for the outer diameter of the wire and the surface finish to reduce the corona on the wire surface (that is, the electric field makes the surrounding local air electrically dissociate, which will increase the line loss.
Although the overhead wire structure is simple, its function is extremely important. In the power network, its line length accounts for more than 90% of the total, especially the 110kv-500kv high-voltage transmission and distribution lines. Bare stranded wire can be divided into three types from the structural composition.
One is stranded with a single wire of a single metal material, such as aluminum stranded wire, copper stranded wire, aluminum alloy stranded wire, etc.;


The second type is ACSR cable ,which uses steel stranded wire as the core wire to increase the tensile strength, and the steel core aluminum stranded wire is twisted with one or several layers of aluminum wire or aluminum alloy wire ;The third type is stranded wire made of bimetallic single wire, such as aluminum-clad steel stranded wire.
Steel core aluminum stranded wire (ACSR) is the most widely used variety. Because the steel core can withstand the tensile force suspended on the pole, the spacing between poles can be increased to reduce investment (especially high-voltage lines), extend the life of the wire, and enhance safety.
If there is corrosive gas around the laying line (such as salt spray at the seaside, chemical plant area), anticorrosive steel core aluminum stranded wire coated with anticorrosive paint should be used.

The development trend of new overhead wire and cables products is: ①Increase the tensile strength and vibration resistance without increasing the weight of the wire, such as high-strength aluminum alloy stranded wire, self-damping (anti-vibration) wire, etc.; ②Increase the long-term working temperature of the wire Or conductivity to increase the transmission capacity, such as double-capacity wire, etc.; ③Anti-icing and snow wire to prevent the surface of the wire from freezing in cold areas.

3. Soft wiring and braided wire
This is a kind of special purpose products with a lot of varieties but a small amount; such as brush wires of electric machinery, parallel wires of batteries, antennas, ground wires and shielding nets. This kind of product is made of thin copper single wire stranded and twisted; battery parallel wires are generally made into flat shape (commonly known as braided wire); shielding net sets are woven and sheathed outside the wires that require shielding.

4. Profiles and profiles
The cross-sectional shape of the product is different, and the product that is not round is called the profile; the product that is not used with a larger length is called the profile. According to its purpose, it can be divided into three types:
① As copper and aluminum busbars for high-current bus bars (also called bus bars). Most of them are flat, and some are made into hollow rectangles and semi-arches. Used in power plants and substations to transmit large-capacity streams; and in switch cabinets. In recent years, insulated bus bars with insulating layers have been developed.

②Wires for catenary. This type of wire is used for overhead wires for electrified railways, urban trams, electric locomotives in tunnels (such as subways, underground mine cars). Due to the large-scale development of urban rail transit lines and electrified railways, the use of catenary wires (commonly known as tram lines, now referred to as contact lines) has doubled. In addition to the technical requirements of the contact wire, in addition to good electrical conductivity, sufficient tensile strength and good weather resistance, excellent wear resistance is also very important, which is directly related to the service life.
③Special-shaped strips are mainly used for commutator components in various motors, as well as blade electrodes of various switches and guillotines. The cross-sectional shape is trapezoidal, unimodal, bimodal, and the material is copper or copper alloy.