The Siemens 6ES7921-3AC00-0AA0 is a front connector module designed for the SIMATIC S7-300 system, specifically for use with 2A digital output modules. It provides the physical and electrical interface between the output module and field wiring via a 20-pole front connector and a flat ribbon cable connection. Rated at 60 V DC and 1 A per channel, with a total current capacity of 4 A across all channels, this module handles the power distribution for the output bank. The 24 V DC rated supply for the logic side is typical for S7-300 backplane power. Mounting is direct to the S7-300 rail or panel, with the terminal block positioned at the top for easy access during wiring. The spring-clamp connection for the power supply accepts stranded wire from 0.25 to 1.5 mm², stripped to 6 mm.
Wiring and connection details
The module uses a 16-pole IDC connector for the flat ribbon cable to the output module, and four spring-clamp terminals (2 x L+, 2 x M) for the 24 V DC power supply feed. Up to two wires per connection are allowed, with a maximum outer insulation diameter of 3.1 mm for the supply terminals. For flexible conductors with core-end processing, use ferruled ends per DIN 46228 without plastic collar, ferrule length 5 to 7 mm. Without ferrule, the same 0.25 to 1.5 mm² range applies. Solid conductors are not supported — stranded or finely stranded only. Maximum wire length between the front connector module and the terminal module is 30 m. The recommended screwdriver blade width for the spring-clamp actuation is 3.5 mm.
It is not a new introduction nor flagged for phase-out — it remains a standard, orderable line item for S7-300 system builds and spares.