3 A D-Curve MCB for High-Inrush Three-Phase Loads
The Siemens 5SY4303-8 is a 3-pole miniature circuit breaker from the SENTRON series, rated 3 A at AC with a D tripping characteristic. The D curve means it tolerates short-duration inrush currents 10–20 times the rated current — the right choice for motor starters, transformers, or solenoid banks where the startup surge would nuisance-trip a B or C curve breaker. Breaking capacity is 10 kA per EN 60898 for general distribution, 35 kA per IEC 60947-2 for industrial panel duty, 15 kA at DC per IEC 60947-2, and 5 kA per UL 1077 / CSA C22.2 No.235. The 35 kA figure is the one that matters for high-fault-current industrial switchboards — it clears a bolted fault without cascading upstream.
Panel Fit and Temperature Derating
Width is 54 mm (3 modular units on a DIN rail), depth 76 mm, height 90 mm. The quick-assembly fastening method snaps onto the rail without tools; mounting position is any orientation. Installation depth of 70 mm means it sits flush in a standard 80 mm deep enclosure with room for wiring behind. Rated current derates with ambient temperature: 3 A at 35 °C, 2.78 A at 45 °C, 2.71 A at 50 °C, 2.62 A at 55 °C, 2.54 A at 60 °C. If the panel ambient runs above 35 °C, the load current must be reduced accordingly — a common oversight in sealed enclosures with multiple breakers ganged together.
Active Production — Sourced to Order
Sourced through independent distribution against an RFQ. For a project milestone, submit the BOM quantity and target delivery date — the supply channel can lock in the allocation to protect the commissioning window.