Siemens SENTRON 5SQ2270-2YA03 — 2-pole C-curve MCB, 3 A, 400 V AC
The Siemens SENTRON 5SQ2270-2YA03 is a 2-pole miniature circuit breaker with a C tripping characteristic, rated at 3 A and 400 V AC at 50 Hz. It provides a breaking capacity of 3 kA per EN 60898, which is the standard for overcurrent protection in residential and commercial final circuits. This unit switches the neutral conductor (2-pole switching with neutral), a feature required for single-phase circuits where the neutral must be disconnected for full isolation. It fits into standard distribution boards on a DIN rail, occupying 2 width units (roughly 36 mm).
The C-curve characteristic (5–10× In) is chosen for circuits with a moderate inrush current — for example, a small compressor or a group of LED drivers — where a B-curve would nuisance-trip and a D-curve would allow too much energy through before opening. This is typical for final sub-circuits in a domestic or light commercial distribution board where the upstream fault level is limited. Overvoltage category 3 (rated impulse withstand voltage 4 kV) means it is suitable for fixed installations where the mains supply is not subject to direct lightning strikes. Energy limiting class 3 indicates the breaker limits the let-through energy (I²t) to a low level, reducing thermal stress on downstream wiring and equipment during a fault. This is a standard performance level for modern MCBs.
The 55 mm installation depth fits standard flush-mount distribution boards and enclosures with a 45 mm or 58 mm back-box depth. The snap-on DIN rail mounting allows tool-less installation and removal. The 2-pole width (2 width units) occupies the same footprint as a standard single-pole MCB pair, so it replaces an existing 2-pole breaker without re-spacing the DIN rail.