What this RCCB does on the line
The Siemens 5SM3622-4KK14 is a 2-pole residual current circuit breaker (RCCB) from the SENTRON 5SM3 series, rated 25 A at 230 V AC and 50/60 Hz. It's a short-time delayed design (Type B+ fault current detection), meaning it handles smooth DC residual currents plus high-frequency AC components — common on drives, UPS systems, and PV inverters where standard AC/DC-sensitive RCCBs might nuisance trip. The 3 kA surge current resistance handles the inrush from capacitive loads or nearby lightning-induced transients.
Thermal derating and conductor sizing
The 25 A rating holds at ambient up to 45 °C. Above that, derate linearly: 24 A at 50 °C, 23 A at 55 °C, 22 A at 60 °C, 21 A at 65 °C, 20 A at 70 °C. If your panel runs hot (near a drive or transformer), the 20 A floor at 70 °C still covers most 20 A branch circuits without upsizing the RCCB. Terminals accept solid or stranded copper from 1.5 mm² up to 25 mm² — covers everything from a 1.5 mm² lighting circuit to a 25 mm² feeder. The 70 mm depth and 90 mm height are standard for this class; no panel cutout surprises.
It's a fast mover in the RCCB category — the 25 A B+ type is a common spec for European-style panels with VFD or UPS loads. Keep it on the shelf if your facility runs mixed DC/AC residual current circuits.