The ABB 2CDS273001R0405 S203M-B40 is a three-pole miniature circuit breaker from the System Pro M Compact S200M family, rated 40 A with a B tripping curve, 440 V AC, and a 10 kA breaking capacity. This is the part you reach for when you need a standard 40 A branch-circuit protector in a 3P DIN-rail footprint for a distribution board or sub-panel.
At 40 A per pole, this covers feeder circuits for lighting, small motor groups, or transformer primaries within the 10 kA prospective fault level. The 440 V AC rating handles line-to-line voltages common in three-phase panels.