Calculation method of monitoring engineering wire rod and auxiliary materials

In the process of making the scheme, the wire configuration is often encountered, such as wire length calculation, wire selection, pipe slot selection, etc. according to the above problems, the wire configuration method is sorted out.
Cable length estimation
The cable length estimation can be divided into two cases: with drawings and without drawings:
1. Drawings available
Find out the route on the drawing and determine the location of the monitoring room; If it is a building project, the distance and location of the off-line well in the monitoring room shall be determined. If it cannot be confirmed, it must be understood by the business.
The general wiring principle of engineering construction is to take a straight line nearby and try not to detour. The longest distance line length of a single gun is generally the sum of the length and width of the building area plus the length of the downline in the monitoring room and the reserved line at the front end.
The standard calculation length of a line is: 1.5m is reserved for the front-end gun, and 3.5m is reserved for the rear-end gun from the ceiling to the ground, that is, the vertical distance from the ceiling to the monitoring cabinet. 2m is reserved for the monitoring cabinet (for short-distance movement of the cabinet). In this way, the reserved line length of a gun is 1.5 + 3.5 + 2 = 7m, and then the total length of the line is calculated according to the length dimension marked in the actual environment of the drawing.
The building is 40m long and 30m wide. The monitoring center is located in the middle of the room. Then the length of gun a line is 40m + 15m (half of 30m width) + 7m (reserved line) = 62m. However, according to the actual work experience of the engineering department, the cable corners and turns are also required in the wiring process, which will generally increase by 15% on the basis of the original length, that is, 62 * 10% = 10m, Then the actual length of gun a is 62m + 10m = 72m.
The length of line for gun B is 10m + 15m + 7m = 32m, plus 15%. The total length of line for gun B is 37m. Then prepare 110m 75-3 video line, rvv2 * 0.5 power line and rvvp3 for both guns × 0.5 monitoring cable is enough. The length of pipe slot is the same as that of cable.

2. No drawing
In the absence of drawings, you need to know the basic information of the network from the business, such as building height, area, line well location and other basic information. Then estimate the vertical length according to the floor height (the general floor height is 3.5m, and the first floor is 7m), and then calculate the approximate total length of the cable according to the transverse distance of the cabinet offline well.
3. Elevator wiring
If there is an elevator in the building wiring, the floor from which the cable enters the elevator shall be calculated according to the following formula: floor ÷ 2 + 1, and the calculated result is the actual number of floors. Take a 16 storey building as an example, 16 ÷ 2 + 1 = 9 should be wired at the 9th floor to enter the elevator.
Selection of cable type
Generally, 75-3 and 75-5 lines are selected as video lines, and there are also a few special lines such as Elevator dedicated lines. The 75-3 video transmission distance is generally 200m, and the 75-5 transmission distance is generally 400m. The power cord is selected according to the actual situation.
At present, the power supply distance of 24V and 12V transformers commonly used by the company shall not exceed 50m. A single transformer can supply 6 guns, up to 7 guns. The power consumption of a single branch is generally 5-12w, and rvv2 * 0.5 two core wire is enough.
Power line diameter quick look-up table
What type of wire should be selected? Firstly, it is necessary to determine which layer the front-end equipment is mainly concentrated on. If the wiring distance exceeds 50m and there are many guns, the power line can be wired by bus, and the transformer can be placed in the front-end equipment box.
According to the quick look-up table of power line diameter, the maximum current load of 3 *. 075 line diameter is 4a. One gun is calculated according to 10W power consumption, and the number of guns available for a power line with 3 * 0.75 line diameter is 88. The calculation formula is 4A * 220V / 10W = 88. On the contrary, it can also be calculated according to this formula that how thick wire 10W * 88 / 220V = 4A is required for 88 guns, and then check the comparison table 4a, and the wire diameter is 3 * 0.75.