The Siemens 5SU1353-6KV40 is an FI/LS-protector Type A (PSE/SSF) combining residual current and overcurrent protection in a single 1+N-pole unit. Rated at B-curve 40A with 30mA sensitivity and 4.5kA breaking capacity, it covers final circuits needing both earth-leakage and short-circuit protection in a compact 70mm-wide package.
The Type A classification means it detects pulsating DC residual currents as well as sinusoidal AC — essential for circuits with single-phase rectifiers, switching power supplies, or variable-speed drives that generate smooth DC fault currents. Standard Type AC devices would not trip on those waveforms. The B-curve 40A overcurrent element trips instantaneously at 5 to 10 times rated current (200–400A), sized for resistive and moderate inductive loads like lighting banks, small motor circuits, or socket outlets. For industrial panels with higher SCCR, verify coordination with the upstream device.