The Siemens 6ES7405-0RA02-0AA0 is a SIMATIC S7-400 PS405 power supply that delivers 20 A at 5 V DC to the backplane bus — no base load required — and provides up to 1 A at 24 V DC for the I/O bus, idling-proof. It accepts a wide DC input range spanning 24 V DC, 48 V DC, and 60 V DC, with rated output currents of 7 A, 3.2 A, and 2.5 A respectively at those voltages.
The 20 A at 5 V DC is the headline figure — it powers the S7-400 backplane bus and all modules plugged into it. Unlike some supplies that require a minimum load on the 5 V rail, this one needs no base load, so it's stable even with a lightly populated rack. The wide DC input (24/48/60 V DC) makes this a single SKU for plants running mixed DC voltage levels — common in process industries where 24 V control and 48 V or 60 V field devices coexist. At 24 V DC it delivers 7 A; at 48 V DC, 3.2 A; at 60 V DC, 2.5 A. The input is primary/secondary rated, so it can be configured for redundant or isolated feeds. The supply occupies 2 slots in the S7-400 rack and measures 50 mm wide, 290 mm high, 217 mm deep. That's a standard double-width S7-400 footprint; it fits any UR1, UR2, or CR2 rack without panel modification. Typical power loss is 44 W, with active power input of 168 W. Inrush current peaks at 56 A with a 1.5 ms half-width — brief enough that standard upstream breakers won't nuisance-trip. Mains buffering holds the output for 20 ms on a power dip, and it meets NAMUR recommendations for process plants.
Approvals include BIS (India), CCC (China), and FM approval (Class I, Division 2, T4, 0 °C to 60 °C). Overvoltage category II. Equipment protection class I with protective conductor. The FM rating makes it suitable for hazardous locations where gas groups are present.
Electrical connection uses 3x 1.5 mm² solid or stranded wire with end sleeve, accepting an external diameter of 3 mm to 9 mm. The terminal design matches standard S7-400 connector blocks. Short-circuit protection is built in. An optional backup battery (2x lithium AA, 3.6 V / 2.2 Ah) can be fitted for memory retention during extended power loss.