Selection of motor control cabinets

Regarding the classification of low-voltage distribution cabinets, there are traditionally two types: one can be divided into fixed cabinets, fixed plug-in cabinets, and drawer cabinets; the other can be divided into fixed cabinets and drawer cabinets； The two classifications are similar with some differences; in the case of fixed plug-and-play cabinets, the cabinet itself is fixed, while the low-voltage components inside the cabinet are of a plug-and-play type. Therefore, we sometimes also classify fixed plug-and-play cabinets as fixed cabinets. There are three installation methods for components: fixed, plug-in, and pull-out. Abroad, especially in developed countries in Europe and the United States, fixed cabinets are used **more frequently than drawer cabinets. The comparison between the two is as follows: Fixed cabinets have advantages over drawer cabinets in the following aspects: 1. Quality of electrical connections. The quality of an electrical connection depends primarily on two factors: the effective contact area (the area that plays a decisive role in the electrical connection) and the pressure applied to this effective contact area. In the fixed cabinet, the connection between the functional units and the power distribution busbars is achieved using bolts, with the effective connection area being the circular region covered by the washers ； The drawer cabinets are connected using contacts, while the functional units and power distribution buses rely on point contact, which results in a reduced effective contact area. The pressure applied at the bolt connection points can be controlled through the tightening torque, thereby achieving the best possible connection quality. In drawer cabinets, if the clamping force on the plugs is too high, it not only makes it difficult to insert and remove the drawers but also tends to wear out the busbars. For these reasons, the electrical connection quality in drawer cabinets is far inferior to that in fixed cabinets. Due to the poor quality of electrical connections, the busbars tend to wear out easily. Moreover, some domestic manufacturers produce contacts of low quality, which results in significant heating in drawer cabinets. The components are exposed to harsh operating conditions for extended periods, making electrical failures more likely; this problem is particularly severe when the circuit current is high. 2. Mechanical structure reliability. The structure of fixed cabinets is relatively simple, and various interconnections can be easily implemented. In drawer cabinets, to facilitate use, some more complex mechanical structures need to be added; due to issues with manufacturing precision, these mechanical structures can easily become sources of failure in the equipment. At the same time, high-power drawers are heavy in themselves, making them difficult to operate, and they can also easily cause damage to the mechanical mechanisms. 3. Equipment maintenance-free operation time. Fixed cabinets require little maintenance due to their simple and reliable design, whereas drawer cabinets have numerous potential failure points, including primary and secondary connectors, the crimping of primary and secondary wires, mechanical operating mechanisms, and power distribution buses, which necessitate regular maintenance. 4. Cost. Drawers require primary and secondary connectors as well as mechanical operating mechanisms, all of which increase the cost of the complete set. Despite the aforementioned issues with drawer cabinets, they are still widely used in industrial applications where high power supply continuity is required, as it is necessary to quickly replace damaged functional units. So how do you choose between drawer cabinets and fixed cabinets? We believe that fixed cabinets are the best choice for distribution circuits. Distribution circuits often have high currents, which requires high standards for the quality of electrical connections. Moreover, Schneider circuit breakers are of stable quality, with a very low likelihood of failure; basically, no components need to be replaced during operation. For situations where circuit breakers need to be replaced promptly, it is recommended to use plug-in circuit breakers. Thanks to Schneider’s guarantees in terms of manufacturing processes, the plug-in base of this type of circuit breaker ensures high-quality electrical connections, while also allowing for quick replacement of the circuit breaker while the switchgear is still powered on. At the same time, removing the circuit breaker unit creates a visible break point, ensuring the safety of maintenance personnel. It is recommended to use drawer cabinets for important motor protection circuits. The motor protection function unit contains numerous components; the use of drawer cabinets facilitates quick replacement of these components in case of failures. At the same time, for motors with higher power, fixed cabinets are still recommended due to reasons related to the quality of electrical connections and mechanical operation. Currently, users in certain domestic industries such as metallurgy and power plants require fixed cabinets or soft starters for circuits with a power rating of over 75 or 90 KW.