The MaxiBus series of bus bars are all rated at 250 Amps AC or DC, 300 Volts AC and 48 Volts DC. This series of busbars is considered the medium duty part of the Blue Sea Systems range. This makes them suitable for use in DC systems with most large alternators and with light duty inverters. For systems with bigger inverters a heavier duty busbar range is available. Although these busbars are rated for AC use they are probably bigger than is needed for that application for most small and medium sized yachts.
These bus bars are sold without covers because they are most often used for negative connections where a cover is not mandatory. An optional cover is sold separately. They are used for consolidating wires, often negative wires in the battery area of a DC system. The application brief by Blue Sea Systems gives more details of their suggested uses.