Residual current protection for high-current feeders
The Siemens SENTRON 5SM3615-6KK is a 2-pole residual current circuit breaker (RCCB) rated 125 A with a 300 mA trip threshold, type A, for 230 V AC 50 Hz systems. The 125 A rating makes this a fast mover for main incomers or sub-feed protection in commercial and industrial distribution boards where standard 63 A or 80 A units won't carry the load. The 300 mA residual sensitivity is the standard for fire protection and general shock prevention in fixed equipment circuits — it's not for personal shock protection (that's 30 mA), but it's the right pick for feeders where nuisance tripping from leakage on long cable runs is a concern. The instantaneous design (no intentional delay) clears faults as fast as the fault current allows, so it's suited for direct feeder protection rather than selective coordination with downstream RCDs.
Snaps onto DIN rail (REG) per the standard 36 mm width, occupying 2 modular width units. Depth is 70 mm, which matches the standard 70 mm installation depth for SENTRON RCCBs — verify gland plate clearance if the enclosure back wall is tight, but this is the common depth for the series.