What the ratings mean for fit
The Siemens SENTRON 5SM3747-5 is a 4-pole selective RCCB (residual current circuit breaker) rated 80 A at 40 °C and 45 °C, with a 500 mA residual trip threshold. The Type B characteristic means it detects smooth DC fault currents and mixed-frequency AC/DC residuals — essential on drives, UPS, or PV circuits where standard AC/DC-sensitive (Type A) devices would miss a fault. The selective (S-type) design introduces a deliberate short-time delay so that downstream RCCBs trip first, keeping this unit as the main switch — no nuisance blackout of the whole panel for a downstream ground leak. Short-circuit withstand is 10 kA per IEC 61008-1 (0.8 kA per EN 60898), which covers most sub-distribution boards fed from a transformer of typical impedance. The I²t let-through is rated 70 000 A²·s, so coordination with an upstream MCCB or fuse is straightforward — the energy the RCCB passes is bounded enough to protect the busbar and downstream terminals.
Derating and thermal behaviour
The 80 A rating holds at 40 °C and 45 °C. Above that, derate linearly: 76.8 A at 50 °C, 73.6 A at 55 °C, 70.4 A at 60 °C, 67.2 A at 65 °C, and 64 A at 70 °C. If the panel ambient runs hot — common in sealed enclosures with drives — the continuous load must be trimmed accordingly. The operating ambient range is -25 °C to 45 °C; storage range is -40 °C to 75 °C.
Panel integration and mounting
Snap-on DIN rail (REG) mount, 4 MW width (72 mm), installation depth 70 mm, overall depth 77 mm. Fits any standard DIN-rail enclosure; the top or bottom feed works, and the SIGRES function remains live even in the off state when fed from the bottom. IP20 with conductors connected — suitable for enclosed distribution boards only, not for wet or dusty locations.