The Siemens 5SU1654-7KV40 is a combined residual current and overcurrent protective device — an RCBO — in a single 1+N-pole module. It integrates Type A residual current detection at 300 mA with a C-curve thermal-magnetic overcurrent trip set at 40 A, all rated for a 10 kA breaking capacity. The 70 mm depth means it sits flush in a standard DIN-rail distribution board without protruding past the gland plate, which matters when you're packing multiple ways into a tight enclosure.
Type A residual detection responds to AC sinusoidal faults and pulsed DC faults. The 300 mA sensitivity is for equipment and fire protection, not personnel protection. In a panel with a 10 kA SCCR rating upstream, this device coordinates without requiring a current-limiting backup fuse — it clears the fault itself. The C-curve (40 A) means the magnetic trip activates between 5× and 10× In, so 200–400 A instantaneous. That suits motor-starting loads, small compressors, and pump circuits where inrush would nuisance-trip a B-curve device. For a purely resistive load like heating elements, a B-curve sibling would be a better match; this one is sized for moderate inductive inrush.