What the 5SM3748-0 is and what it does
The SENTRON 5SM3748-0 is a 4-pole residual current operated circuit breaker (RCCB), type AC, rated 100 A at 400 V AC with a 500 mA tripping fault current. It is an instantaneous design, meaning it trips without a time delay when the residual current exceeds 500 mA. This covers the basic earth-leakage protection requirement for a 4-wire (3-phase + neutral) supply in a distribution board.
Ratings and what they mean for fit
The 100 A rating at 400 V AC (50 Hz) is the continuous current capacity for resistive and motor loads within the RCCB's thermal limits. The 500 mA residual current trip threshold is higher than the standard 30 mA used for personal shock protection; it is typically specified for equipment protection or where high leakage from filters or drives would nuisance-trip a lower-sensitivity device. The 4-pole configuration switches all three phases and the neutral, so it fits a 3P+N distribution board without a separate neutral link.