6ES7421-1FH20-0AA0 - Digital Input Module - SIEMENS

SIMATIC S7-400 SM 421, 16 inputs 120/230 V, industrial reliability

Aimed at plant operators, automation engineers and maintenance teams, the SIMATIC S7-400 SM 421 digital input module meets the needs for safe mains signal acquisition. It provides 16 isolated digital inputs suitable for 120/230 V in AC or DC. This capability allows direct connection of power contacts, mains-output sensors or existing cabinet status signals without intermediate relays. The 1500 V AC isolation test, 12 W power loss and a controlled 80 mA consumption contribute to stable integration into your S7-400 rack. Part of SIEMENS' SIMATIC family, this module plugs natively into S7-400 architectures and is intended for industrial environments where electrical robustness, availability and ease of implementation take precedence over complex interfacing. You get a proven component designed to limit failure points and secure the automation chain.

Productivity, electrical safety and easy integration

• Direct connection at 120/230 V AC/DC – Eliminates interface relays, reduces wiring and cabinet space, and speeds up commissioning.
• 16 isolated digital inputs – Improves immunity to interference, limits undesired coupling and increases acquisition reliability.
• 1500 V AC isolation test – Contributes to installation safety and resistance to transient overvoltages encountered in industrial settings.
• 12 W power loss, 80 mA consumption – Controls thermal and power budgets for predictable cabinet sizing.
• Native SIMATIC S7-400 compatibility – Immediate integration into existing projects, seamless software continuity and simplified maintenance.

Technical architecture and build quality

The SM 421 belongs to the SIMATIC S7-400 Digital I/O family. It provides 16 digital inputs suitable for 120/230 V in AC or DC, with galvanic isolation between electronics and field wiring. The module has been tested at 1500 V AC, reinforcing its dielectric strength in environments subject to disturbances. The 12 W power loss and 80 mA consumption allow accurate planning of thermal dissipation and rack power budget. Hardware and software compatibility with SIMATIC S7-400 automation systems ensures seamless integration into existing configurations. Manufactured in Germany, it reflects strict quality control and consistent performance. All these characteristics target stable operation, reliable diagnostics and long-term use in demanding industrial conditions, without adding unnecessary complexity to wiring or maintenance.

Typical uses and applications

The SM 421 is used to capture high-voltage discrete states from power interfaces, proximity switches with mains outputs, auxiliary safety elements or contactor status feedback. It is suitable for process production lines, special machinery, site utilities, infrastructure and OEM installations where 120/230 V signals are standard. Operations teams gain a reliable way to integrate heterogeneous inputs without multiplying interface stages.

Differentiation, consistent performance and longevity

The combination of 16 isolated channels, direct S7-400 compatibility and support for 120/230 V AC/DC positions this module as a robust solution when interfacing with mains-level signals is required. SIEMENS' expertise in industrial controllers ensures long-term availability and functional consistency across the SIMATIC range. For maintenance managers, this translates into reduced drift risks, a standardized fleet and faster interventions. German origin traceability reinforces confidence in specification stability and manufacturing quality.

Get back to production faster with Standard Exchange Industry. Benefit from fast availability, options for exchange unit, new or refurbished parts, plus expert repair services. Request your quote for the SM 421 6ES7421-1FH20-0AA0, delivery 24 to 72 h depending on stock and warranty up to 24 months depending on service.