Siemens SENTRON 5SU1342-7KC40 RCBO — 40 A, 30 mA, Type A, 50 kA
The Siemens SENTRON 5SU1342-7KC40 is a 4-pole RCBO (residual current circuit breaker with overcurrent protection) rated at 40 A with a 30 mA type A residual current trip and a C tripping characteristic. It carries a 50 kA breaking capacity per EN 60898 and IEC 60947-2, which means it can safely interrupt fault currents up to that level without upstream cascading — critical for high-fault-capacity installations like industrial distribution boards or commercial mains. Rated for 50 Hz supply and 690 V AC, this unit switches the neutral conductor and is designed for any mounting position with a 70 mm installation depth. The IP20 protection class applies when installed in a distribution board with conductors connected — standard for panel-mount RCBOs.
Key ratings and what they mean for fit
The 40 A rated current with C characteristic handles motor inrush and transformer energization without nuisance tripping. The 30 mA type A residual current trip detects pulsating DC fault currents as well as sinusoidal AC. The 50 kA breaking capacity (Icn/Ics) at 690 V AC is the headline figure for selectivity coordination — it matches the fault level at the service entrance in most European industrial installations, so you don't need a backup fuse or upstream breaker with higher rating unless the prospective short-circuit current exceeds 50 kA. Energy limiting class 3 means it restricts let-through energy, reducing stress on downstream equipment during a fault. Conductor cross-section range of 0.75 to 35 mm² solid or stranded covers everything from control wiring to main feeder cables. The screw terminals require 2.5 to 3 N·m torque — standard for a 40 A device. Halogen-free and silicon-free construction matters for installations in environments sensitive to corrosive off-gassing, such as data centers, hospitals, or marine panels.
Panel integration and mounting
The 5SU1342-7KC40 occupies 2 width units (36 mm on a standard DIN rail) and accepts supply from either top or bottom — flexible for busbar or cable entry in a distribution board. The 70 mm installation depth fits standard 100 mm deep enclosures with room for wiring. Ambient temperature range of -25 to +55 °C covers most indoor panel environments; storage range of -40 to +75 °C handles shipping and warehouse conditions. Overvoltage category III means it's rated for fixed installation downstream of the main distribution board, not for plug-in equipment. The touch protection feature (finger-safe terminals) reduces arc-flash risk during maintenance when the panel door is open.