The Siemens 5SU1356-6KV40 is a combined residual-current and miniature circuit breaker (FI/LS protector) in a single 70 mm wide unit. It integrates Type A residual-current detection at 30 mA with a B-curve overcurrent trip set at 40 A, all rated for a 6 kA breaking capacity. This is the 1+N-pole variant, meaning it switches and protects the phase conductor while the neutral is switched but not protected against overcurrent — standard for single-phase final circuits where neutral protection is not required by local code.
What the ratings mean for fit
The 30 mA residual-current threshold (IΔn) is the standard for personal protection against direct contact in residential and commercial final circuits — it will trip within 300 ms at rated residual current, fast enough to prevent ventricular fibrillation per IEC 60364. Type A detection means it responds to sinusoidal AC fault currents AND pulsating DC fault currents (e.g. from half-wave rectified loads like LED drivers, switched-mode supplies, or variable-speed drives), which a standard AC-only RCD would miss. The B-curve overcurrent characteristic (40 A rated current, In) means the magnetic trip activates at 3 to 5 times In (120–200 A), suited for resistive and general-purpose loads with moderate inrush — think lighting banks, socket outlets, small heaters. The 6 kA breaking capacity (Icn) is the maximum prospective short-circuit current the device can safely interrupt at its rated voltage; this is adequate for most domestic and light commercial distribution boards where the upstream fault level is below 6 kA. The 70 mm width (4 module spaces) is wider than a standard single-module MCB — account for this in DIN-rail layout and enclosure fill calculations.