Selective main MCB for distribution boards
The Siemens SENTRON 5SP3720-1 is a selective main miniature circuit breaker (MCB) designed for residential and infrastructure distribution boards. It is a 3-pole unit rated at 20 A with a 25 kA breaking capacity per EN 60898 at 400 V AC, 50 Hz. The characteristic E trip curve provides a delayed response, making it suitable for selective coordination — upstream of downstream MCBs with lower ratings, so a fault on a branch clears without taking the main breaker out.
Occupies 6 width units (roughly 108 mm) on the rail. Depth of the enclosure is 92 mm, so it fits standard distribution board depths. Saddle terminals accept conductors from 2.5 mm² minimum up to 50 mm² maximum — sized for the incoming supply cable. The switch position indicator shows OFF = green, ON = red for quick visual status at the panel door.