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common problem
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Wire and cable laying is a common problem encountered
Announcer:格盟泰  Date:2019/11/29 14:28:07  Views:117

Pay attention to the laying of cable trenches. Cables with different voltage levels must be installed in different brackets. The cable trenches themselves must pay attention to drainage measures. And consider measures to prevent small animals such as rats from entering. Regarding the laying of wires and cables, the following points are summarized:


Question 1 How many cables need to be laid with cable trenches?


Answer: According to "Measures 6.10 Section 6.10, the following 8 are recommended to be buried directly, 8 to 12 are recommended to use a pipe, 12 to 18 are recommended to use a cable trench, and 18 or more are recommended to use a cable tunnel." It can be connected with the actual engineering reference, not so fixed. As for cable trenches and cable tunnels, it is not the difference between the number of cables, it is the difference between maintenance and importance.


It mainly depends on factors such as engineering conditions, environmental characteristics, and number of cable types, as well as selection of requirements that meet the requirements for reliable operation, easy maintenance, and technical and economical reasonableness. It is uncertain whether there are mandatory index requirements. The specific scheme can be determined by referring to the relevant content in Section 5.2 of GB50217-2007 P28.


Question 2 How to calculate the current carrying capacity of the cable trench?


answer:


1: (Considering the laying of the bridge, considering that the bridge is in the air, and there is a cover in the cable trench, the derating factor is 0.96.)


2: (For the correlation coefficient of current carrying capacity, please refer to GB T16895.15-2002 "Building Electrical Installations Part 5 Section 523 Wiring System Current Carrying Capacity". Personally, it is more appropriate to consider the coefficient of the ladder frame.)


Question 3 Is there a depth requirement for the cable trench when laying high voltage cables?


A: There are no requirements. The depth of the cable trench is determined by the number of cables and the number of types of cables. For example, there are three levels of control cables, low voltage power cables, and high voltage power cables. The pitch is 250 ~ 300, so the height is determined.


Question 4 Can the busway be laid along the cable trench?


(Additional question: For a project, a high-level hospital, to save money, choose an oil-immersed transformer for outdoor installation, 15 meters away from the building (including 6 meters in the middle), and the low-voltage power distribution room is located in the hospital underground. Use a busway (current-carrying 3000A) to run along the cable trench to the underground distribution room of the building. Is it possible?)


Answer: It should be possible to use dense buses that meet the requirements of the corresponding IP level. For example, Siemens has buses that can be laid underwater. However, the cost of using dense busbars will be relatively high, and it is necessary to comprehensively consider which one is better to use dry transformers and busbars. Personally, it is recommended to use dry-type transformers and place them indoors. The maintenance workload will be less, and the failure rate will be lower.


Question 5 How many cables can be laid in the cable trench without brackets?


Answer: Generally, the bracket is required. If there is no bracket, the cable maintenance in the cable trench will be more troublesome. If the project is not large and the number of cables is not large, it is not a problem, but the heat dissipation conditions will be worse, and if there is water in the trench, it will also affect the cables.


Question 6 Can high and low voltage cables share the same cable trench?


(Additional question: Outdoor cable trench, trench width 1200mm, brackets on both sides, 10KV high-voltage cable on one side, and 1KV-class low-voltage cable and control cable on the other side. Is it in compliance with the specifications? What should be noted?


Answer: The cable trench can be laid together. For specific requirements, see the requirements of Articles 5.1.3 and 5.1.4 of GB 50217-2007 P24.


Question 7 What is the distance between the cable trench and the road?


Answer: This is mainly to consider the force of the cable trench cover. If there is no problem with the force, there will be no problem. Generally set up on the sidewalk or where the motor vehicle does not pass.


Question 8 Is it necessary to use armored cables when laying cables in cable trenches?


(Additional question: Technical measures: When laying cables in cable trenches or cable tunnels, you should consider using steel tape armored plastic outer sheath type cables with anti-ant and rodent-resistant functions. Didn't make it clear! Can you not wear armor?)


A: There is no mandatory requirement for directly buried cables to use armor, and cable trenches are even more absent. The requirements are different according to different environments. (If the rat in the area is rampant, armoring is recommended) Generally there is no mandatory requirement.


Question 9 What is the minimum distance between the high-voltage cable and the low-voltage cable in the cable trench when they are layered on the same side bracket?


Answer: Separate the weak electric cables with metal plates and ground the metal plates at the same time! Best, place an iron plate (or metal slot box) on the uppermost bracket, and the iron plate is grounded. Inside the box).


According to GB 50217-2007 5.1.3 Article 1: Power cables with high to low voltage levels, control and signal cables with strong to weak power, and communication cables should be installed in the order of “top to bottom”. It can then be determined according to GB50054-2011 Table 7.6.23.


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