What this 100 A Class E MCB is for
The Siemens 5SP3791-1 is a SENTRON main miniature circuit breaker (SHU) — a selective, 3-pole breaker rated 100 A with a Class E tripping characteristic. It ships pre-assembled on an SHU adapter (5ST1324) with three enclosed locking caps (5ST1323), so it's ready to drop into a panel as a main incoming device. The 25 kA breaking capacity at 400 V AC (per EN 60898) means it can safely interrupt high fault currents at the service entrance without upstream coordination issues — that's the number that decides whether this breaker clears a short-circuit or the fire department does. Overvoltage category IV tells you it's rated for the utility-side interface, not just downstream distribution.
Sizing and fit — what the ratings mean on the panel floor
At 6 modular width units (roughly 108 mm on a 35 mm DIN rail), this breaker takes up more rail space than a standard 3-pole MCB — that's the trade-off for the 100 A continuous rating and the selective Class E curve. The 20 000 mechanical switching cycles are double what you'd see on a typical 10 000-cycle SENTRON MCB like the 5SL4363-7, which tells you it's built for main-switch duty where it cycles daily, not just fault protection. Operating temperature spans -40 to 70 °C, so it's fine in an unheated enclosure or a warm MCC room. IP20 with conductors connected means it's panel-protected — no washdown rating, no outdoor exposure without a weatherproof enclosure.
Physical integration — DIN rail and enclosure fit
Mounts on 35 mm standard DIN rail per EN 60715, or via screw fixing with accessories. The 92 mm enclosure depth is standard for SENTRON main breakers. Saddle terminals are provided — good for terminating larger-gauge incoming cable without lug adapters. The switch position indicator shows green for OFF, red for ON, which speeds up panel walk-downs. Shock-rated to 30 g at 11 ms and vibration-rated to 2 g across 5–150 Hz, so it holds up in industrial environments with rotating machinery nearby.