The Siemens 6ES7921-3AM20-0AA0 is a 40-pole front connector module for the SIMATIC S7-300 family, designed to connect the I/O wiring to a Compact CPU 313 or 314.
Rated at 60 V DC and 1 A per contact, with a total current limit of 4 A across all pins. That 60 V ceiling covers standard 24 V DC control loops with headroom, but keep the total draw under 4 A — the module's internal bus bar and connector are the bottleneck, not any single pin. The stranded wire range is 0.25 to 1.5 mm², and the stripped length is 6 mm; for finely stranded wire with a ferrule, the range narrows to 0.25–0.75 mm² with a 5–7 mm ferrule length per DIN 46228-1 without plastic collar. Tightening torque for the screw terminals is 0.4–0.7 N·m — a small driver, not a ratchet.
Environmental limits and panel placement
Operates from 0 to 60 °C, stores from -40 to +70 °C. The maximum cable length between this front connector module and the remote terminal module is 30 m; beyond that, voltage drop on the 24 V DC supply and signal integrity start to be a concern. The terminal position is at the top of the module, and the housing is black, non-transparent.