The typical structure or section of a low voltage switchgear consists of three distinct and independent parts: the circuit breaker compartment, the busbar compartment, and the cable compartment.
Each circuit breaker compartment usually accommodates up to 2 air circuit breakers arranged vertically. Each circuit breaker is individually isolated from the other circuit breakers. Behind the circuit breaker compartment is the busbar compartment, which is separated from the circuit breaker compartment by a partition barrier.
Adjacent busbar compartments are isolated from each other by insulating partitions between the compartments. Finally, the cable compartment is located at the rear of the switchgear section and can be optionally separated by a ventilated or non-ventilated barrier from the busbar compartment.
The cable compartment has a hinged door or removable cover for terminating the connections of the line and load cables. This compartment arrangement is the most typical and can be called rear accessible switchgear because access to the back of the switchgear is required.
A variation of the switchgear arrangement is the front-wired switchgear, where the cable compartment is adjacent to the circuit breaker compartment and the cable compartment door is located at the front of the equipment. This arrangement reduces design depth, eliminates the need for rear access, and allows the switchgear to be placed against a wall, similar to a switchboard.
Partitioning of low-voltage switchgear is intended to improve the safety, reliability, and maintainability of the switchgear, for example, by preventing accidental contact with certain conductors such as the main busbar or circuit breakers in adjacent units when maintenance is being performed. Partitioning can also limit some of the damage caused by arc faults and reduce the risk of fault propagation to other parts of the switchgear.
Low-voltage switchgear provides short-circuit and overload protection through circuit breakers with integrated trip units. These low-voltage circuit breakers are available in both fixed and withdrawable versions. Fixed means that the circuit breaker is immovable and can only be operated from the panel of the circuit breaker. Withdrawable means that the circuit breaker can be easily moved to the test and disconnect positions without opening the switchgear and can be completely removed from the switchgear for maintenance.
