Backplane bus supply for S7-1500 racks
The Siemens 6ES7505-0KA00-0AB0 is the 25 W system power supply that feeds the backplane bus of a SIMATIC S7-1500 rack — it converts the 24 V DC field supply into the internal logic voltage the CPU and I/O modules need to communicate. Rated input is 1.3 A at 24 V DC, with a static permissible range of 19.2 V to 28.8 V DC and a dynamic window down to 18.5 V and up to 30.2 V DC — wide enough to ride through a sagging field supply without dropping the rack. It delivers 25 W to the backplane bus and dissipates 6.2 W of its own heat at nominal load — that loss sits inside the enclosure, so factor it into the panel thermal budget.
Protection and hold-up for dirty lines
Built-in short-circuit protection and reverse polarity protection mean the supply handles a miswired 24 V line or a downstream bus fault without letting the magic smoke out — a common headache in field-terminated panels. On a mains/voltage failure, the supply holds up the backplane bus for 20 ms — enough for a CPU with a retentive memory cycle to finish its current scan and enter a defined stop state before the rack browns out. Equipment protection class III with a protective conductor connection means it relies on SELV/PELV supply and the PE bond for fault clearing — standard for control cabinet installations.
DIN-rail fit and environmental limits
IP20 rated — it is open to the cabinet environment, so install it in a clean, dry enclosure; it is not sealed against washdown or dust ingress. Rated for installation altitudes up to 5 000 m, with restrictions above 2 000 m per the manual — the derating at high altitude is due to reduced air density for cooling.
This part carries an active lifecycle status — it is current-production from Siemens, not a phase-out or obsolete line. It is compatible with the SIMATIC S7-1500 platform and is configurable from STEP 7 V5.5 SP3 or TIA Portal V12 onward — no firmware upgrade needed for standard racks.