Siemens 6ES5 421 8MA12 Digital Input Module 8x24VDC

Siemens 6ES5-421-8MA12 Digital Input Module is an eight-channel digital input card for SIMATIC S5 systems, delivering eight independent 24 V DC inputs. The module is described as non-isolated and is intended for use with S5-90U, S5-95U, and S5-100U controllers, as well as the ET 100U and ET 200U distributed I/O families. With 8 inputs rated for 24 V DC, it provides a straightforward interface for sensing switches, sensors, and other 24 V DC devices in older installations. The part is listed under Siemens as 6ES5-421-8MA12 (often cataloged as 6ES5421-8MA12) and is typically sold as a spare part with no direct replacement in current lines. In practice, this module slots into the S5 backplane and communicates status changes to the host PLC, enabling reliable digital input across eight channels without the need for external multiplexing. When integrating into a system, verify compatibility with your specific S5 controller model and ET IO configuration, and follow the manufacturer’s wiring diagrams for correct connection of 24 V DC sources and return paths.