What it is and what it does
The Siemens 5SU9356-7CN40 is a 1P+N RCBO (residual current circuit breaker with overcurrent protection) from the SENTRON series, combining a 40 A C-curve MCB with a 30 mA Type A RCD in a single 2-module-wide unit. It fits standard DIN-rail enclosures and is rated for 230/240 V AC at 50/60 Hz.
Key ratings and what they mean for your panel
Breaking capacity: 6 kA per EN 60898 and 10 kA per IEC 60947-2. The 6 kA figure governs residential/commercial final circuits; the 10 kA rating applies when the device is used under the industrial standard, giving you headroom for higher fault-current installations. The C-curve (tripping between 5 and 10 times rated current) suits motor and lighting loads with moderate inrush. Type A RCD detects pulsating DC residual currents as well as sinusoidal AC — essential on circuits with single-phase rectifiers, variable-speed drives, or switching power supplies where pure AC-sensitive (Type AC) devices may blind. The 30 mA sensitivity provides additional protection against direct contact. Rated current of 40 A at 30 °C ambient (derate at higher temperatures). Power dissipation per pole is 0.75 W at rated load in hot operating state — relevant for thermal coordination in tightly packed enclosures. Insulation voltage rated at 264 V, overvoltage category III, pollution degree 2.
Integration and mounting
Two-module-width (36 mm) design, 77 mm depth, 90 mm height, 70 mm installation depth. Mounts in any position on DIN rail. Supply can enter from top or bottom. IP20 protection applies when installed in a distribution board with connected conductors — standard for enclosed panel use.