Precautions for parallel use of cables

　　First of all, for the two power cables used in parallel, it is best to have the same cable model and specification length, so that when the cables are energized, the various parameters of the two power cables are basically close, the current carrying capacity is basically evenly distributed, and there will be no single cable overload. , A large area of fever and burnt phenomenon occurred in advance.

　　Secondly, the distance between cables running in parallel should be appropriately enlarged, so that when a cable fails, it will not affect the cables used in parallel nearby and burn down at the same time, which reduces the power economic loss of the enterprise to a certain extent.

　　Thirdly, power cables run in parallel. The contact and connection status of the wire noses at both ends of the cable and the switch contacts should be checked frequently to ensure that the cable and the switch are well connected, because most of the cables used in parallel are above 35mm, and the conductor resistance per kilometer is Below zero ohms, the magnitude of the resistance is about 10 -1. If the cable nose is not in good contact with the switch, it is easy to cause a certain phase or phases of a cable at the switch to have too large contact resistance, resulting in two cables carrying capacity The distribution is uneven. The current cable customers take into account economy and grid design, and the selection of cable models and specifications will not leave too much current carrying margin. When the contact resistance at the nose of the cable is too large, first, it will heat up in continuous use. Burning out, in addition, causing the current carrying capacity of the two cables to shift, causing one of the cables to be overheated and burned.

　　There is another situation worth mentioning, that is, when multi-core armored power cables are used in parallel in the AC grid, the A phase, B phase, and C phase of each cable must be taken out separately and connected with the A, B, and C of the switch respectively. C three-phase parallel connection, it is strictly forbidden to short-circuit all the cores of a cable and connect to one phase of the switch. Because the cable is equivalent to running in a live single-phase, single-phase alternating current will generate eddy currents in the steel strip and cause thermal burn accidents in the cable. In addition, the reduction of the current carrying capacity after parallel connection should be fully considered, and the current carrying capacity after parallel connection is not equal to the current carrying capacity of the actual conductor section.

　　Calculation formula for commonly used cable usage in integrated wiring

　　1. Demand for RJ-45 headers and information modules

　　Demand for RJ-45 head: m=n*4+n*4*15%

　　M: Indicates the total demand for RJ-45 connectors

　　N: Indicates the total amount of information points

　　N*4*15%: indicates the surplus left

　　The demand for information modules: m=n+n*3%

　　M: Indicates the total demand for information modules

　　N: Indicates the total amount of information points

　　n*3%: indicates the surplus

　　2. Thread consumption per floor

　　1. Thread consumption per floor: C=[0.55*(L+S)+6]*n

　　L: The farthest information point distance from the management room on this floor

　　S: The distance of the information point closest to the management room on this floor

　　N: The total number of information points on this floor

　　0.55: Spare factor

　　6: Termination tolerance

　　2. C=[0.55(F+N)+6]*m

　　C Thread consumption per floor

　　F is the distance from the furthest information socket to the wiring closet

　　N is the distance between the nearest information socket and the wiring closet

　　m is the number of information sockets on each floor

　　3. Number of wire boxes

　　1. The longest line distance + shortest line distance) / 2 = average

　　(average value + 5 meters) * points = total length

　　Total length/305 (standard meters per box) + 2 boxes = total number of boxes

　　2. Each service requires a 4-pair unshielded twisted pair cable or 2-core (62.5/125 micron multi-mode) optical cable;

　　The total number of horizontal cables in each communication room = (the number of work areas served by the communication room) * (the number of services provided by each work area)

　　Calculation of horizontal wiring in work area:

　　A: The distance of the closest information point;

　　B: the distance of the farthest information point;

　　C: The number of information points in each working area

　　The required cable length for each layer=(A+B)/2*1.1*C

　　The sum of cable lengths of each layer = cable length of each layer * building height

　　Total number of required cable boxes = sum of cable lengths of each layer/305 meters

　　Remarks: 1.1 The coefficient is the loss, and the floor height is the floor height. If the horizontal trunking runs through the ceiling, it must be calculated; if it is a raised floor, it can be ignored;

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