Attention should be paid to the laying of cable trenches. Cables of different voltage levels should be set up with different brackets, and drainage measures should be taken for the cable trenches themselves. And consider measures to prevent small animals such as mice from entering. Regarding the laying of wires and cables, the following points are summarized:

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

Answer: According to section 6.10 of measure 2009, it is recommended to use direct burial for less than 8 wires, pipe laying for 8-12 wires, cable trench for 12-18 wires, and cable tunnel for more than 18 wires. These are all suggestions and can be referenced in actual engineering, and are not so fixed. As for cable trenches and cable tunnels, it is not the difference in number, but the difference in maintenance and importance.

The selection mainly depends on factors such as engineering conditions, environmental characteristics, cable types and quantities, as well as meeting the requirements of reliable operation, easy maintenance, and technical and economic rationality. It is uncertain whether there are mandatory indicator requirements. The specific plan can refer to the relevant content in section 5.2 of GB50217-2007 P28.

Question 2: How to calculate the current carrying capacity of cables laid in cable trenches?

Answer:

1: (Considering the installation of cable trays, taking into account that the trays are in the air and there are cover plates in the cable trench, the capacity reduction factor is 0.96.)

2: The correlation coefficient of current carrying capacity can refer to GB T16895.15-2002 "Electrical installations of buildings - Part 5, Section 523- Current carrying capacity of wiring systems". In my opinion, it is more appropriate to consider the coefficient of the ladder frame. )

Question 3: Is there a depth requirement for the laying of high-voltage cables and cable trenches?

Answer: There are no specific requirements. The depth of the cable trench is determined by the number and type of cables you have, such as control cables, low-voltage power cables, and high-voltage power cables. Generally, three layers are set up with a spacing of 250-300 between each layer to determine the height.

Question 4: Can the bus duct be laid along the cable trench?

(Question supplement: For the first project, a high-rise hospital, in order to save money, oil immersed transformers are selected for outdoor installation, 15 meters away from the building (including a 6-meter road in the middle). The low-voltage distribution room is located underground in the hospital. To save investment, I want to use a busbar duct (carrying 3000A current) to lay along the cable trench to the underground distribution room of the building. I wonder if it is feasible?)? )

Answer: It should be possible to use dense busbars that meet the corresponding IP level requirements, for example, Siemens has busbars that can be laid underwater for operation. However, the cost of using dense busbars will be relatively high, and it is necessary to comprehensively consider which is better, choosing a dry-type transformer or using busbars. Personally, I suggest using a dry-type transformer and placing it indoors. The maintenance workload will be smaller, and the failure rate will also be lower.

Question 5: How many cables can be laid in cable trenches without brackets?

Answer: Generally, a bracket is required. Without a bracket, cable maintenance in the cable trench will be more complicated. If the project is not large and there are not many cables, it is okay not to install them, but the heat dissipation conditions will be poorer, and if there is water in the trench, it will also affect the cables.

Question 6: Can high and low voltage cables be laid in the same cable trench?

(Additional question: Outdoor cable trench, with a width of 1200mm, supports on both sides, with 10KV high voltage cable on one side and 1KV low voltage cable and control cable laid on the other side. Does it comply with the specifications?)? What should be noted? )

Answer: It is possible to lay cables in the same trench. Specific requirements can be found in GB 50217-2007 P24 5.1.3 and 5.1.4.

Question 7: What is the distance between laying the cable trench parallel to the road?  

Answer: This mainly considers the force on the cable trench cover plate. If there is no problem with the force, there should be no problem. Usually set on sidewalks or in places where motor vehicles do not pass through.

Question 8: Should armored cables be used when laying cables in cable trenches?

(Additional question: In terms of technical measures, when cables are laid openly in cable trenches or cable tunnels, consideration should be given to using steel tape armored plastic outer sheath cables with anti ant and anti rodent functions. However, it seems that this is not explicitly stated in the specifications! Can cables be installed without armor?)

Answer: There is no mandatory requirement to use armor for buried cables, let alone cable trenches. According to different environmental requirements, armor is generally not mandatory (if rodent activity is rampant in the local area, armor is recommended).

Question 9: What is the minimum distance between strong and weak electrical cables when laid in layers on the same side bracket in a cable trench?

Answer: Separate the weak current cables with metal plates and ground the metal plates at the same time! It is best to place an iron plate (or metal slot box) on the top bracket, ground the iron plate, and place the weak current cable on the iron plate (inside the slot box).

According to Article 5.1.3 of GB 50217-2007, power cables with voltage levels from high to low, control and signal cables from strong to weak, and communication cables should be installed in a "top-down" order. According to Table 7.6.23 of GB50054-2011, it can be determined.