High and low voltage of UL891 low-voltage cabinet

The shortage of power equipment in the United States is severe, so many customers come to China to find products. Our switchgear manufacturing capabilities have already become the world's number one.

As the most widely used and widely used low-voltage switchgear, UL891 has a high demand in North America. As a low-voltage switchgear, Chinese people have rich experience and do not pay attention to standards or technical requirements, as long as the functions are implemented.

UL891 is relatively simple compared to high-end switchgear in China. It has a box type structure, mainly consisting of fixed frame circuit breakers and molded case circuit breakers for outgoing lines. The dead front has a fixed front cover plate structure, and all live parts such as incoming lines, copper bars, and outgoing cables are sealed inside the box. The basic power distribution function is achieved by only using the operating handle (operating button) that exposes the cover plate for opening and closing operations.

So various types of UL891 distribution boards emerged, which had to be impressed by the creativity of some people. There are so many smart people.

The typical layout of UL891 group molded case circuit breakers according to American standards should be as follows: the middle circuit breaker is installed horizontally, and both sides are used for cable channels.

The Korean production is like this, with two circuit breakers in a row for 250A and below, with wires on both sides and independent space on both sides for cable connection. The middle circuit breaker is designed with modularity, and each cover plate covers a row of circuit breakers

Some of our manufacturers produce it this way, with a single cover plate covering all the molded case circuit breakers from top to bottom, instead of using a single cover plate for a row of circuit breakers.

Another option is to cover the entire width of the switchgear with one cover plate, or to cover several molded case circuit breakers with one cover plate. There are no separate cable channels and cover plates.

For frame circuit breakers, two cover plates are sufficient, whether for ventilation or installation of instruments, buttons, indicator lights, etc. with wiring, as well as fixed or withdrawable circuit breakers, or cable connection spaces, all use one cover plate, which seems to meet the requirements of UL891.

Save as much as possible. One steel plate, one screw, UL891 with lowered standards, although usable, may not be rejected by some customers, but there are still significant issues and potential hazards.

The typical UL891 has its design criteria, fully considering electrical safety, on-site cable connection, operation and maintenance support, and later expansion and supplementation requirements. After considering these requirements, through patterned and standardized design, the maximum convenience of functional satisfaction and large-scale production in different application environments is achieved.

It is not enough to simply install the components and connect the copper bars with the front cover plate.

1. Cable channel, with both sides and upper and lower spaces, is specifically used as a cable channel. During installation and maintenance, there is no need to open the circuit breaker cover plate. The cover plate that needs to be repaired can be removed without removing excess covers, which will not affect the cables that do not need repair and eliminate potential risks.

2. The bending radius requirements for cables vary depending on the current specifications. Different cable diameters and bending radius requirements result in insufficient space, which leads to incomplete bending of the cable. This inevitably results in additional stress on the cable connection, making it unreliable. Prolonged operation, combined with electric force, can exacerbate temperature rise and cause faults. A high current frame circuit breaker requires the installation of several or more cables per phase, which requires a large space. Therefore, a separate cover plate is needed for easy installation and inspection.

3. A significant feature of UL891 is its flexibility, ease of modification and expansion, and the ability to replace circuit breakers on site according to load conditions. Regular American standard manufacturers adopt modular design, and whether it is vertical busbars or plastic shell circuit breaker installation plates and cover plates, they are all produced in modular form. On site changes can be made quickly without affecting circuits that do not require modification, making it fast and simple.

Therefore, UL891 has a provision for the vacancy factor of the current carrying capacity of vertical busbars, which means that if a group of 48 modular molded case circuit breakers can be installed, only a part of the space is actually installed. If only 30 modules are installed, the vacancy factor is 1.5, which means that the current carrying capacity needs to be selected based on 1.5 times the total current to ensure that the future installation circuit current meets the requirements.

4. For the use of withdrawable frame circuit breakers or secondary wiring such as instruments and indicator lights that require maintenance, an openable door panel should be used, and after the door panel is opened, it should comply with the UL1558 low-voltage metal armored power switchgear compartment requirements to ensure that the live parts are not touched after opening the door.

5. Ventilation design is crucial, not just decoration. Just a few blinds are enough, but it's not. UL891 has a high installation density, NENA 1 protection level, and box structure to ensure that high current use will not cause overheating problems.

Some manufacturers' UL891 distribution panels only aim to save time, without considering on-site installation and maintenance, as well as potential problems that may arise in future use, which poses a hidden danger to customers.

Therefore, customers who use American standard switchgear need to keep their eyes open and truly check the design and structure of the product. They should not only aim for affordability, but also pay more for future use.