Siemens 5SN6420-8CP — 4-Pole MCB for 400 V Distribution
The Siemens 5SN6420-8CP is a 4-pole miniature circuit breaker from the SENTRON 5SN family, rated for 400 V AC at 50 Hz.
Two breaking-capacity figures matter for coordination studies. For a panel fed by a 630 kVA transformer with a prospective short-circuit current around 12 kA, the 15 kA rating keeps selectivity intact without cascading to upstream devices. The 4-pole design switches all three phases and neutral simultaneously, which avoids single-phasing on three-phase motor loads.
Snap-on mounting to standard 35 mm DIN rail. Depth of 76 mm and height of 90 mm match the SENTRON 5SN family envelope; the 72 mm width (4 MWU) means it occupies four adjacent 18 mm module positions. Terminals accept solid conductors up to 35 mm² — sufficient for the outgoing feeder on a 40 A to 63 A three-phase circuit.
DC Rating and Multi-Phase Operation
The DC-side rating goes up to 72 V maximum, which suits control-circuit protection in DC bus applications within that voltage ceiling. For AC multi-phase operation the maximum operating voltage is 440 V — the same for single-phase and multi-phase connections, so the breaker can be used on a 400/440 V three-phase system or on a single 277 V line-to-neutral leg. Power loss per pole at rated current in hot state is 1.6 W; for a 4-pole breaker that totals 6.4 W dissipated inside the enclosure, worth factoring into thermal calculations for a densely populated panel.