American standard low-voltage switchgear

The American standard low-voltage switchgear is designed and produced based on the IEEE C37.20.1 standard and UL1558 safety requirements.

As a primary distribution switchgear, it is connected to UL891 secondary distribution panel, UL891 distribution box, UL845 motor control cabinet, etc., and requires complete cascade control and protection functions.

Therefore, in a broad sense, C37.20.1 armored low-voltage switchgear, UL891 low-voltage distribution panel, and UL845 low-voltage motor control cabinet are all low-voltage switchgear. Unlike the GB7251/IEC61349 series switchgear, different functional units can be used together. The American standard switchgear has significant differences, and the conventional product composition is also completely different.

IEEE C37.20.1/UL1558 low voltage switchgear only uses withdrawable frame circuit breakers, metal armored separate metal compartments - circuit breaker compartment, instrument compartment, vertical busbar, horizontal busbar compartment, cable connection compartment, high safety requirements, can open cabinet door structure, cabinet door

The UL891 low-voltage distribution panel is mainly composed of fixed circuit breakers, which can be frame circuit breakers or molded case circuit breakers. UL891 requires a Dead front structure, which uses a cover plate fixed with screws at the front to prevent easy opening of the cover plate and requires specialized tools to open it.

The requirement of Dead front is determined based on the structural form of the box type switchgear. The box type structure, including circuit breakers and other components, busbars, mounting plates, etc., are all installed in a shared box without separation. That is to say, when the front cover is opened, the busbars and other live equipment that can be touched by hand are unobstructed, like a black box. All components are installed together, and only professionals can open and maintain them.

The advantages of the box type switchgear structure are also quite obvious. Due to the lack of a grounded functional compartment partition, the installation of live parts and components is more compact. The fixed plastic shell circuit breakers installed in groups are directly fixed with copper bars and vertical busbars at the incoming terminals, without the need for installation plates, resulting in high installation density. The cable is directly connected to the outlet end of the molded case circuit breaker, and the cable is directly inserted into the terminal with its own tightening screw.

Box type structure, no partition obstruction, good ventilation and heat dissipation conditions, simple installation and maintenance, lower cost, smaller volume, and simpler operation.

Therefore, for American standard low-voltage switchgear, different applications have different requirements. The first level distribution, armored structure, high safety and power supply continuity, withdrawable components, metal partitions, and one component failure can be removed for maintenance, while other functions such as main busbar and incoming cables can continue to operate with electricity, similar to the loss of operational continuity level LSC 2B of medium voltage switchgear.

Separate compartments for relay protection and other functions, electrically operated, open cabinet doors for maintenance, safe and convenient. However, UL891 generally does not have secondary control equipment and can be operated manually.

Currently, many UL891 data center projects also require a lot of secondary equipment such as multifunctional meters and circuit status indicator lights, which face issues of safety and convenience in operation and maintenance. In principle, it cannot be completely enclosed in a box structure, and the secondary instrument compartment needs to be separately sealed with door panels instead of Dead front. When the cabinet door is opened, it will not touch any charged bodies or mechanical moving parts