Selective main MCB for service-entrance coordination
The Siemens 5SP3740-1 is a SENTRON 5SP3 selective main miniature circuit breaker — 3-pole, rated 40 A at 400 V AC, 50 Hz, with a 25 kA breaking capacity per EN 60898. The E tripping characteristic means it's designed for selective coordination upstream of downstream MCBs: it holds a short-time delay so a fault on a branch clears without taking the main breaker out. That's the difference between a partial line drop and a full panel blackout in a residential or infrastructure distribution board. Rated insulation voltage sits at 690 V, overvoltage category IV, surge voltage resistance 6 kV — it's built for the utility-side of the meter, not just downstream sub-panels. The 25 kA SCCR at 400 V matches typical transformer-fed service-entrance fault levels in European TN systems.
Mounting and conductor interface
Mounts on 35 mm standard DIN rail via the included SHU adapter 5ST1324, or on busbar, or screw-fixed with accessories. It occupies 6 width units (roughly 108 mm) on the rail. Conductor cross-section range is 2.5 mm² minimum to 50 mm² maximum — that's a wide enough throat to accept the incoming service cable directly without a separate terminal block. Saddle terminals are fitted, which grip stranded conductors more positively than a screw-and-plate arrangement. IP20 with connected conductors — protected against finger contact but not water ingress, so it belongs inside a locked enclosure, not in a washdown area. The switch-position indicator shows OFF = green, ON = red, which is standard for European panel practice.