SENTRON 5SY7340-7 — 3-pole C-curve MCB for panel and machine builds
The Siemens SENTRON 5SY7340-7 is a 3-pole miniature circuit breaker with C-curve tripping characteristic, designed for 400 V AC operation at 50/60 Hz. It carries a dual-rated breaking capacity: 15 kA per EN 60898-1 and 20 kA per IEC 60947-2, with a DC rating of 15 kA at 60 V per IEC 60947-2. The C-curve (5–10× In) handles moderate inrush from motor starters, small transformers, and fluorescent lighting banks — the typical mix in a machine control panel. Mounts on DIN rail via the quick-assembly system in any orientation. At 3 modular width units (54 mm wide, 76 mm deep, 90 mm tall), it occupies the same footprint as a standard 3P MCB — no panel rework needed when replacing an existing unit. The IP20 rating applies with conductors connected, which is the normal installed state inside an enclosure.
Breaking capacity and selectivity — what the dual rating means for coordination
The 15 kA rating under EN 60898-1 is the value used for residential and light commercial coordination per IEC 60364. The 20 kA rating under IEC 60947-2 applies when the breaker is specified for industrial duty — the higher figure reflects the standard's more demanding test sequence (including O-CO at rated service short-circuit). For a panel fed by a transformer with a prospective fault current above 15 kA but within 20 kA, the 60947-2 rating is the one that governs the SCCR label. The DC rating of 15 kA at 60 V covers DC auxiliary circuits fed from the same bus. Energy limitation class 3 means the breaker limits let-through energy to a level that protects downstream components during a short-circuit — relevant for coordinating with downstream contactors and motor starters. Pollution degree 3 and overvoltage category III suit it for fixed installations in industrial environments where conductive pollution is possible.
Thermal derating and environmental limits
The breaker is rated for ambient temperatures from -40 °C to +75 °C, but the continuous current must be derated above 55 °C. The evidence specifies a derating curve: max 95 % humidity at 55 °C, dropping to max 55 % at 70 °C and max 35 % at 75 °C. In a sealed panel with multiple breakers ganged together, this derating matters — the C-curve's thermal trip element responds to ambient heat, so a tightly packed row near the top of the enclosure may nuisance-trip if the internal temperature exceeds 55 °C without applying the derating factor.
Compliance and documentation
Certified to IEC / EN 60898-1 and IEC / EN 60947-2, with UL 1077 recognition for the North American market (5 kA at AC per UL 1077 / CSA C22.2 No.235). The breaker is halogen-free and silicon-free, which matters for applications sensitive to outgassing (clean rooms, medical equipment, sealed enclosures with sensitive electronics). Sealable terminals are standard — allows the panel builder to lock the cover after commissioning.