Siemens 5SY8420-8 — D-curve 4-pole MCB for high-inrush loads
The Siemens 5SY8420-8 is a 4-pole (4P) miniature circuit breaker from the SENTRON series, with a D tripping characteristic rated at 20 A and a 30 kA breaking capacity per IEC 60947-2 at 400 V AC. At 400 V AC the unit delivers its full 30 kA SCCR; under DC per IEC 60947-2 it interrupts 15 kA, and under UL 1077 / CSA C22.2 No. 235 it is rated 5 kA. That 30 kA figure gives real headroom for high-fault panels without cascading upstream breakers. Rated current is temperature-dependent: 20 A at 45 °C, 19.5 A at 50 °C, 18.98 A at 55 °C — so in a warm enclosure you need to account for the derating. Physical footprint: 72 mm wide (4 modular width units), 90 mm tall, 76 mm deep (70 mm installation depth). Mounts in any position on the quick-assembly system (DIN rail).