48 V DC, 20 A — the thermal budget is the real constraint
The Siemens 6EP3447-8SB00-0AY0 is a SITOP PSU8200 series DIN rail power supply delivering a rated 20 A at 48 V DC from a 400–500 V AC three-phase input. The headline number is 20 A continuous, but the operating envelope matters more: the rated range is 0–20 A from 0 to +60 °C, then derates 4 %/K up to +70 °C with natural convection. At 65 °C ambient, that drops the usable current to about 16 A — a detail that decides whether this unit holds up in a warm cabinet.
Efficiency, MTBF, and the failure-mode read
At 94 % efficiency, the PSU8200 wastes about 64 W at full load — that heat has to leave the enclosure, and the derating curve is the consequence. The MTBF at 40 °C is 520,782 hours, which pencils out to roughly 59 years mean time between failures under ideal conditions. In a real panel at 50 °C with full load, expect the MTBF to drop by roughly half per 10 °C rise above the rating point — a standard reliability rule for electrolytic-cap-limited supplies. The I²t value at maximum is 2.24 A²·s, which governs the inrush profile for upstream breaker coordination. The feeder recommendation calls for a 3-pole 10–16 A C-curve MCB or a Siemens 3RV2011-1DA10 set at 3 A. That selectivity window is tight — if the panel already uses B-curve breakers, the inrush may nuisance-trip on first power-up.
Clearance, mounting, and approvals checklist
Required free space: 40 mm above and below for convection airflow, but 0 mm on the left and right sides — so it can be ganged directly against adjacent modules without side gap. Approvals include cULus listing under UL 508 and CSA C22.2 No. 107.1 (File E197259), plus cCSAus to UL 60950-1 and CSA C22.2 No. 60950-1. Also carries CE, EAC, and DNV GL marine certification. No ATEX, IECEx, or UL hazloc approval — this is a general industrial and marine-grade supply, not for explosive atmospheres.