Overview
The 6ES7421-1EL00-0AA0 is a Siemens SM 421 digital input module for the S7-400 system, providing 32 isolated inputs rated for 120 V AC/DC. It draws 6.5 W from the backplane and occupies a single-wide slot on the rack.
Function & operation
Each of the 32 channels accepts a nominal signal of 120 V at 47 to 63 Hz AC, or 80 to 132 V DC, with a typical input current of 2 mA (2 to 5 mA range). The module also responds to a 0 to 20 V UC range for low-level detection. Switching current per channel is 1 mA. Isolation between channels and the backplane is tested at 1500 V, supporting reliable operation in electrically noisy environments. Status LEDs on the front panel indicate the logic state of each input for quick commissioning and fault isolation.
Applications
This SM 421 module is used in Siemens S7-400 racks for medium to large automation systems — process plants, power generation, water treatment, and factory lines — where 120 V AC/DC discrete signals from pushbuttons, limit switches, proximity sensors, or relay contacts need to be brought into the controller.
Lifecycle & availability
Siemens has classified the 6ES7421-1EL00-0AA0 as phase-out, with a discontinuation date of 2025-10-01. After that date, the module will no longer be manufactured. Buyers should evaluate last-time-buy options or plan for a migration to a current S7-400 input module. No official successor order code is listed in the available documentation.