Selective main MCB for high-fault-current panels
The Siemens 5SP3791 is a SENTRON selective miniature circuit breaker (SHU) — a main breaker designed to discriminate with downstream MCBs so that only the faulted branch trips, keeping the rest of the distribution board live. Rated 100 A at 230 V AC with a 25 kA breaking capacity per EN 60898, it handles the full fault current at the service entrance without cascading upstream. The E tripping characteristic (short-time-delay magnetic release) is what makes it selective: it holds through the instantaneous trip zone of downstream C- or B-curve breakers, clearing only on sustained overcurrent or a hard fault that exceeds its delayed threshold.
What the ratings mean for fit
Breaking capacity of 25 kA at 230 V AC means this breaker can safely interrupt a fault current up to 25 000 A — typical for a main distribution board close to a transformer. Overvoltage category IV (pollution degree 3) confirms it is rated for the utility-side interface, not just downstream branch circuits. The 1-pole form factor occupies 2 modular width units (about 36 mm) on standard DIN rail, so it takes up two adjacent slots in the enclosure. Mechanical life of 20 000 switching cycles is typical for a main breaker that sees infrequent manual operation.
Panel integration notes
Mounts on standard DIN rail (35 mm per EN 60715). Depth of 91 mm (92 mm into the enclosure) and height of 145 mm — verify the enclosure lid clearance, especially if a busbar cover or sealable flap is fitted. Saddle terminals accept copper conductors; the breaker is sealable for utility-lockout compliance. IP20 with connected conductors means it is protected against finger contact but not against water ingress — indoor panel use only. Ambient range -40 °C to 70 °C covers most indoor electrical rooms.