The Siemens SENTRON 5SY8404-8 is a 4-pole miniature circuit breaker with a D tripping characteristic, rated 4 A at 45 °C ambient on a 400 V AC system. On DC circuits it's rated 15 kA per IEC 60947-2, and under UL 1077 / CSA C22.2 No. 235 it carries 5 kA at AC — relevant if the panel ships to North America under those standards. The 4-pole version (4P) switches all three phases plus the neutral — common in three-phase distribution where the neutral needs overcurrent protection or is switched for isolation. Mounting position is any; the quick-assembly system clips onto the standard DIN rail, occupying 4 modular width units (about 72 mm).
Temperature derating and environmental limits
The 5SY8404-8 is rated 4 A at 45 °C, but the current must be derated as ambient rises: 3.9 A at 50 °C, 3.8 A at 55 °C. Above that, the surrounding temperature influence curve caps at 95% relative humidity up to 55 °C, then 55% RH up to 70 °C, and 35% RH up to 75 °C maximum. The minimum storage/operating temperature is -40 °C, covering cold-start conditions in outdoor or unheated installations.
Mechanical and vibration withstand
Tested to IEC 60068-2-6 for vibration resistance: ±1 mm displacement at 5 to 25 Hz, and 50 m/s² acceleration at 25 to 150 Hz. That covers most industrial panel vibration environments — motor starters, conveyor lines, compressor skids — without the breaker nuisance-tripping or loosening on the DIN rail. Overvoltage category III and degree of pollution 3 confirm it's rated for fixed installations inside the distribution board, not for the final outlet.