What this RCCB does and where it fits
The Siemens 5SM3747-4 is a 4-pole residual current circuit breaker (RCCB) from the SENTRON family, rated 80 A at 40 °C and 45 °C with a 500 mA residual trip current. It's a Type B device — that means it detects smooth DC residual currents in addition to AC and pulsating DC, so it's the right pick for variable-frequency drives, UPS systems, and PV inverters where DC fault currents can flow. The short-time delayed switching function gives it selectivity with downstream RCCBs: it holds through brief inrush or leakage pulses that would nuisance-trip a standard unit.
Ratings that matter for panel integration
Snaps onto DIN rail (REG profile) and can be mounted in any position — handy when you're squeezing it into a crowded enclosure. The 72 mm width takes up 4 modular units on the rail. Depth is 77 mm, installation depth 70 mm, so it clears a standard 80 mm deep enclosure back wall. IP20 rating applies once the distribution board is installed with conductors connected — that's typical for a panel interior; no special washdown sealing needed. The short-circuit current rating is 10 kA per the device's own withstand, and it's also rated 0.8 kA according to EN 60898 and IEC 61008-1 — that's the standard for RCCB coordination with an upstream MCB or fuse. Overvoltage category III means it's rated for fixed-installation distribution level, not just downstream equipment.
Thermal derating — don't ignore it
The 80 A rating holds up to 45 °C ambient. Above that, it derates: 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 your panel runs hot — say next to a drive or inside a sealed cabinet — size the upstream protection for the derated current, not the nameplate 80 A. Operating ambient range is -25 °C to +45 °C; storage range is wider at -40 °C to +75 °C.