For the user, how to choose a variety of products of various specifications and models?
For commercial and residential buildings and factory distribution systems, GCK and GGD cabinets should be used. The utility model has the advantages of simple interchange, small occupied area, high power supply continuity and reliability, convenient and safe maintenance and installation, and can be combined with a program controller and a microprocessor to provide an automatic power supply control system, which can be used as power receiving, feeding and power control. equipment. Such products are increasingly being used in many projects.
For systems with high motor load, such as power plants, petrochemicals, steel mills, or for substations, high-rise buildings, hospitals, stadiums, airports, ports, mining, etc., MNS and GCS cabinets are ideal. The drawer unit has a large installation space, the drawer and the functional isolation board are made of flame-retardant materials, and the safety protection level is high; the GGD cabinet is suitable for power distribution in the factory workshop, which is economical and convenient, and is easily accepted by the grassroots electrician. The disadvantage is low protection level. For cabinets, soft starter cabinets, control cabinets, etc. that control large motors in water plants, power plants or factories, they can be used because they are basically non-standard installation methods except for the cabinet frame. In summary, the selection of the power distribution cabinet should be based on the load application to select a cost-effective product.
2. Main components of low voltage distribution cabinet
In order to prevent the manufacturer from selecting low-cost components and affecting the performance of the power distribution cabinet in the future, it is necessary to select components that have passed the inspection and have guaranteed quality. When ordering, the user should indicate the model specifications and brand of the main components such as the frame, circuit breaker and transformer. Among them, the circuit breaker is divided into two categories: omnipotent (also known as frame type, internationally known as ACB) and plastic case type (known internationally as MCCB, MCB (small)). Of course, in the process of technical disclosure, it is sometimes necessary to accept the rationalization proposals of the manufacturer to avoid the use of technical indicators that far exceed the distribution load requirements, resulting in unnecessary investment, material waste and maintenance costs.
3, low-voltage power distribution cabinet implementation standards
The product standards for low-voltage switchgear and control equipment are: IEC 60439-1, GB7251.1-1997, GB9466-88, JB/T9661-1999, etc. The manufacturer can perform production and organize acceptance according to the standard requirements. Inspect the manufacturer's standard implementation and production management level. Often the management level of the company is closely related to the quality of the product. Users can understand the relevant standards and select a manufacturing plant with a certain production capacity before inspecting the production plant.
4, material quality requirements
4.1 The material of the distribution box and distribution cabinet is preferably hot-rolled, and the thickness of the steel plate should be greater than 1.2mm, and the corrosion resistance is good.
4.2 Whether the internal components of the power distribution cabinet (box) meet the design and specification requirements, whether the quality of the components is reliable, mainly depends on whether the components are produced by regular electrical manufacturers, whether they are counterfeit and shoddy products, whether the electrical performance is reliable, quality assurance Whether the information is complete.
How to identify the quality and authenticity of product quality depends on the accumulation of ordinary experience and careful observation, as well as a high degree of responsibility. When it is not certain, you can find similar authentic products for comparison, or ask the construction unit to test.
5, installation quality control points
5.1 When the cabinet is darkly laid, the requirements are as follows: 1 If the dark box is larger than 30cm, the prefabricated beam plate must be placed at the top (except for the lightweight partition). Before the wall is built, the construction unit should be prefabricated in advance. 2 The dark case should be careful not to highlight the stucco layer. This part is a place that is prone to problems. It must be controlled in advance, and then reworked after painting is completed, and civil construction is not allowed.
5.2 box (cabinet) metal frame and basic section steel must be grounded or connected to zero reliably. The door can be opened with electrical appliances. The grounding terminal of the door and frame should be connected with bare braided copper wire and marked. The ground wire must be connected directly to the ground.
5.3 Three-phase four-wire system Repeated grounding Zero row and ground row must be connected by two-color line. This part is often overlooked. Repeated grounding flat iron must directly enter the cabinet, and the two-color line is directly connected to the ground row. The flat gaskets and anti-loose washers at both ends of the connecting line are complete and the wiring is tight.
5.4 The cross-sectional area of ​​the main line of the grounding wire shall comply with the provisions of Table 6.1.2 of the Code for Acceptance of Construction Electrical Engineering Construction (GB50303-2002). This part is also easily overlooked.
5.5 In-box incoming line: 1 must be entered according to the prohibited side and back of the wire tube inside the box. 3 The pipe grounding of the metal pipe must be drawn from the box and the cabinet floor.
5.6 In-box wiring should meet the following requirements:
a. The wiring is neat and there is no splicing. The wiring inside the box is arranged horizontally and vertically, and tied with a tie. The construction personnel are required to first plan the distribution of all the wires according to the circuit conditions inside the box and then start wiring. At the same time, note that the wires connected to the ground row and the zero row should be bent 90 degrees, and then connected to the zero row and the ground in a vertical direction.
b. The wires are tightly connected. The number of wires on the same terminal is not more than 2, for example, 2 wires, and the middle is separated by a flat gasket. Lock washers and flat washers are available. The anti-loose gasket is easy to be neglected, and the wiring screw is also untightened. These problems must be checked out and rectified, otherwise the wiring is loose, the contact resistance is increased, and the terminal is easily burned out. The bending direction of the wire on the terminal is also easy to ignore. When bending into a circle, the direction of the bending must be the same as the direction of rotation of the receiving screw. When the screw is tightened, the radius of the circle will not become large, causing some of the wire to leave the gasket. . For aesthetic reasons, bending into a circle must be regular, and the wire going down or up is just in the middle of the circle.
c. Set the zero line and ground line busbars in the cabinet respectively. The neutral line and the protective ground line must be led out through the bus bar, and the zero and ground row marks should be complete.
d. The remaining amount of wire in the cabinet can be basically kept at 1/2 half of the circumference. However, the “excessive†wire is often cut during wiring, resulting in insufficient margin, affecting acceptance and future use. The problem is often that when the zero row or ground row is directly close to the incoming line, the wire is directly connected to the terminal block and the "extra" line is cut. It should be picked up after the side of the box, so that it can meet the margin requirements.
e. It is strictly forbidden to trace the back of the box, otherwise it will easily cause eddy current loss.
f. When the cross section of the multi-strand wire (copper core wire) is less than 2.5mm2, tighten the tin-tin or the connecting terminal and connect with the terminal; if the cross-section is larger than 2.5mm2, the terminal is connected to the terminal after the terminal is connected. Before the multi-strand wire is connected with the plug-in terminal, the end should be tightened with tin. The connecting terminal must be tightly pressed, and the pressing line should be pressed horizontally by two or more.
g. Check the jumper section in the box, whether it is a finished box or an assembly box, it is easy to have problems. The author has seen many times that the incoming line section is much smaller than the outgoing line section. This situation must be discovered and rectified in time to avoid problems in the distribution box in the future.
5.7 The distribution box function number and circuit number must be complete. The function number refers to the switch name number attached to the outside of the electric box for future use and maintenance; the circuit number is the number on each circuit in the box, which is consistent with the system diagram.
5.8 There is also a problem that is prone to problems, that is, there are more lines on both sides of the box, and the two screws of the fixed distribution box panel are just on the sides of the box, and must be separated from the wires on both sides, otherwise the screws are very It is easy to damage the wire insulation, causing the case to be charged or shorted.
6, worth noting a few questions
6.1 Linkage problem with diesel engine backup power supply: Diesel engine backup power supply has self-injection and self-cutting, mechanical and electrical interlocking; mains signal is sent from power distribution screen to diesel engine control panel; equipped with test function.
6.2 The power distribution room with cable trench wiring should consider the problem of floor load bearing, and the cable inside the cable trench should be laid in layers to avoid the formation of eddy currents and heat.
6.3 Ventilation of power distribution rooms should be considered together on site.
6.4 Whether the clearance of the power distribution room meets the installation requirements. In summary, with the continuous development of the power industry, the power system has higher and higher requirements for safety and economic operation. The low-voltage complete equipment distribution device plays an important role, and the smooth completion of the project is time is beneficial. The needs of the economic era.
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