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.
What the ratings mean for fit
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. The 10 kA breaking capacity at the rated voltage covers most commercial and light industrial installations where the prospective short-circuit current stays under that level. 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.