## How to prevent cable from fire due to conductor overload

During the operation of wires and AAC Cables, they will heat due to the existence of resistance. The resistance of the conductor is generally very small, and its heating power can be expressed by the formula q = I ^ 2R. Q = I ^ 2R shows that for a section of conductor in actual use (r has been basically constant), the greater the current passing through the conductor, the greater the heating power; If the electric flow is constant, the heating power of the conductor is also constant. The heat released during operation will be absorbed by the conductor itself, resulting in the increase of conductor temperature. Although the conductor keeps absorbing the heat released by current work during operation, its temperature will not rise indefinitely. Because the conductor is absorbing heat and constantly releasing heat to the outside world, the facts show that the temperature rises gradually after the conductor is powered on, and finally the temperature is constant at a certain point. At this constant point, the heat absorption and release power of the conductor are the same, and the conductor is in thermal equilibrium. The ability of conductor to withstand high temperature operation is limited, and operation beyond a certain maximum temperature will be dangerous. This maximum temperature naturally corresponds to a maximum current. If the conductor exceeds this maximum current, it is overload. The overload of the conductor directly leads to the temperature rise of the conductor itself and its nearby articles. Temperature rise is the most direct cause of this kind of fire.

Overload destroys the insulation layer between double stranded conductors, causing short circuit, burning equipment and fire. The double strand conductors are separated by the insulating layer between them. Overload softens and destroys the insulating layer, resulting in direct contact between the two strands of conductors, causing short circuit and burning the equipment. At the same time, the high temperature generated by large current at the moment of short circuit causes the line to catch fire and fuse, and the generated molten beads fall to combustibles to cause fire. Overload temperature rise can also directly ignite nearby combustibles. The heat transfer of overload conductor increases the temperature of nearby combustibles. For combustibles with low ignition point nearby, it is possible to ignite them and cause a fire. This danger is particularly prominent in warehouses for storing inflammables and buildings with easy and combustible decoration.
Overload also puts the connection in the line under overheated conditions, which accelerates its oxidation process. Oxidation causes a thin layer of oxide film that is not easy to conduct electricity at the connection point. The oxide film increases the resistance between the contact points, resulting in ignition and other phenomena, resulting in fire.
So, how to prevent fire caused by overload of wires and ACAR Cables?
1. In the process of line design, the capacity of the site shall be accurately verified, the possibility of new capacity in the future shall be fully considered, and the appropriate type of conductor shall be selected. For large capacity, thicker conductor shall be selected. Line design and reasonable type selection are the key steps to prevent overload. If the design and selection are improper, it will leave congenital hidden dangers that are difficult to rectify. Some small projects and places are not carefully designed and selected. It is very dangerous to choose and lay lines at will. The bearing capacity of the original line shall be fully considered for new electrical appliances and electrical equipment. If the original line does not meet the requirements, it should be redesigned and reconstructed.

2. The line shall be laid by qualified electricians in accordance with relevant specifications. The laying conditions of the line directly affect the heat dissipation of the conductor. Generally speaking, the line laying shall not pass through inflammable and combustible materials and stacking, which will lead to poor heat dissipation of the conductor, heat accumulation, the possibility of igniting the surrounding combustible materials, and increase the risk of fire under overload; The lines laid in the decoration ceiling of public entertainment places shall be protected by steel pipes to separate the ceiling from the line. Even if there are molten beads under overload, short circuit and other conditions, they will not fall, so as to avoid fire.
3. Strengthen power management, avoid random wiring and grounding, and use mobile sockets carefully. Random ACSR Cables, random grounding and the use of mobile sockets are actually adding electrical equipment to a certain section of the line, increasing the amount of current, which may cause overload. The jack of mobile socket is obviously more than the fixed socket on the wall. If too many electrical equipment are used on the mobile socket, the original line must be difficult to bear. For high-power equipment and electrical appliances, separate lines should be set, and mobile sockets should not be used as wiring sources.

4. Speed up the renewal and transformation of old lines and eliminate potential fire hazards. Due to the long service life of old enterprises, old residential areas and other units, many lines have aged and exceeded the service life. Even if the current carrying capacity of some lines is small, it is difficult for aging lines to bear such current carrying capacity, and it also has the risk of overload. Especially in the old residential areas, the lines have long been aging, but with the improvement of people’s living standards and the increase of household appliances, their power consumption is still increasing year by year, which is really worse. For old lines, timely supervision and coordination shall be carried out to promote their rectification as soon as possible, so as to eliminate potential fire hazards and ensure safety.

## How to Ensure Outdoor Cable Performance ?

Many users and installations are faced with the problem of cheap and efficient data transmission between buildings in the park environment. The choice of routing, transmission distance and application environment will all affect the choice of cable medium. Incorrect or inappropriate choice will result in a shortened period of wiring investment, and reinstallation will also cause the network system to stop running.
If it is an outdoor application, the fiber optic system is usually the choice for campus network connection. The real cost of optical fiber lies in the termination of optical fiber cabling system and optoelectronic equipment. When users only need to transmit 10Mbps or 100Mbps within a distance of 50 meters between buildings, optical fibers are generally not used.

Buying conventional Category 5 copper cables underground or laying overhead may cause transmission failure of a certain network along the wiring line. Therefore, choosing the existing outdoor direct-buried enhanced type cable will bring a cheap link. Before deciding to choose these outdoor LAN cables, you should fully understand their design.

Anti-moisture protection nets have been used in communication cables for many years. These aluminum polymer materials have overlapping seals as protection to reduce the penetration path of water vapor to prevent water from entering. However, an unprotected dry cable will need to suffer as long as six months to a year of liquefaction due to infiltration, and a dry cable with a moisture-proof protective net will be completely protected. The cable designed in this way is approximately similar to a foil-screened LAN cable, and it is easy to connect and use.

Therefore, the wiring system designer must consider the application environment, which includes the following environment and parameters that affect the cable:
1. Whether the cable is placed under the eaves; as long as the cable is not directly exposed to sunlight or ultra-high temperature, the standard LAN cable can be used. It is recommended to use pipes:
2. External walls; avoid direct sunlight on the walls and man-made damage;
3. In the pipe (plastic or metal); if in the pipe, pay attention to the damage of the plastic pipe and the heat conduction of the metal pipe;
4. For suspended applications/overhead cables, the sag and pressure of the cable should be considered. Which bundling method you intend to use. Whether the cable is directly irradiated by sunlight; laying directly in the underground cable trench, this environment is the smallest control range. The installation of the cable trench should be checked regularly for dryness or humidity;
5. Underground pipeline. In order to facilitate future upgrades, cable replacement, and isolation from surface pressure and the surrounding environment, laying pipes is a better method. But don’t expect that the pipe will always remain dry, which will affect the choice of cable types.

Factors affecting cable performance include:
1. Ultraviolet (UV)-Do not use cables without UV protection in direct sunlight. You should choose cables with black polyethylene or PVC sheaths, such as Brand-Rex’s 4 pairs of reinforced type 5 MegaOutdoor outdoor cable, with metal mesh moisture-proof protective layer and black polyethylene sheath, is suitable for most inter-building connections, whether it is overhead laying, ground installation or pipeline construction, it can be used:

2. Heat-the temperature of the cable in the metal pipe or trunking is very high. Many polymer materials will reduce the service life at this temperature. Black polyethylene or PVC sheathed power cable should be selected;

3. Water-Water is the real killer of LAN cables. The moisture in the twisted-pair cable of the local area network will increase the capacitance of the cable, thereby reducing the impedance and causing near-end crosstalk problems. If it is extremely effective to prevent moisture and water vapor, a protective layer of metal shielding net is required;

4. Mechanical damage (repair costs)-the repair of optical cables is very expensive, and at least two terminations are required at each discontinuity;

Grounding-if the shielding layer of the cable needs to be grounded, the corresponding standards must be followed;

The total length of the route (not only between the buildings)-Use outdoor-grade LAN twisted-pair cables between the buildings, and the total length should be limited to 90 meters.
For a network of 100Mbps or 1000Mbps, the laying distance cannot exceed this limit. If the laying distance is between 100 meters and 300 meters, optical cable should be selected.
The following simple experiments can be used to self-test whether the wiring investment is safe: use a 20-meter enhanced category 5 UTP cable to terminate at both ends; carefully remove the cable sheath at the midpoint of the cable to expose a small section of copper cable (1 cm ); Test the cable according to AN/NZSD standard; soak the cut part of the cable in water for 1-2 minutes, and then retest.