What it is and where it sits
The ABB 1SDA054381R1 is a T5V 400 TMAX molded-case circuit breaker, 3-pole, rated 400 A on the main circuit and built on the 400 AF frame. Uimp is 8 kV, so it sits comfortably in switchboards where impulse withstand is part of the coordination study rather than a hand-waved figure. Electrical endurance is rated at 7000 cycle, 60 cycles per hour, and mechanical endurance at 20000 cycle, 120 cycles per hour. For a feeder breaker that mostly sits closed, electrical cycle life is what governs; for a motor-starter isolation duty or any scheme where the breaker is racked in and out regularly, the 120 cycles-per-hour mechanical figure is the one that caps the maintenance interval.
Panel fit
Overall dimensions run roughly 20.5 cm tall by 14 cm wide by 10.35 cm deep. That footprint is the real number for a panel-builder working out DIN or cubicle cut-out — the shipping mass on the carton is not what you plan mounting around, and the breaker itself sits in the 5.1 Kg class.