The Siemens 5SM3646-4BG is a 4-pole residual current operated circuit breaker (RCCB) rated 63 A with a 300 mA sensitivity, type B characteristic, short-time delayed, for 400 V AC systems. Type B detection covers AC sinusoidal, pulsating DC, and smooth DC fault currents — the full range you get from variable-speed drives, UPS rectifiers, or PV inverters. The short-time delay prevents nuisance tripping on transient ground faults that clear on their own, so it's the right choice for circuits with electronic loads that produce brief leakage spikes.
Mounts on DIN rail in the distribution board alongside MCBs and other modular devices. The 4-pole width (4 modules at 18 mm each) fits standard 4-module cutouts. Type B RCCBs are physically interchangeable with type A or AC in the same enclosure — just confirm the neutral busbar arrangement for the 4-pole configuration.