The Siemens 6ES7921-4BF00-0AA1 is a pre-assembled front connector for SIMATIC S7-400 digital I/O modules. It brings 48 poles on a 5 m cable, rated at 60 V and 1 A per contact, with a total current capacity of 4 A. This is the factory-assembled version — no field wiring of the connector itself, just plug and route the round cables to the terminal module.
The 60 V rated value covers the typical 24 V DC digital I/O signals in an S7-400 rack, with headroom for 48 V field devices if needed. The 1 A per contact is generous for standard digital inputs (typically 10–20 mA) and smaller outputs; the 4 A total limit across all 48 poles means you can't sink a full amp on every channel simultaneously — realistic for mixed I/O but worth noting if you're grouping high-current outputs on one connector. The 5 m cable length is the maximum run between the front connector and the terminal module; plan your cabinet layout accordingly.
Mounts directly to the S7-400 digital I/O module — no adapter or backplane wiring needed. The screw-type terminals on the cable end accept 0.14 mm² round conductors (pre-assembled). Position the terminal module within 5 m of the rack; the cable exits at the top of the connector. No end cover plate required.