SIEMENS 6ES7921-5AK20-0AA0 S7-300 Communication Module | Replacement, Equivalent & Selection Guide
The SIEMENS 6ES7921-5AK20-0AA0 is a front connector / communication interface module designed for the SIMATIC S7-300 PLC series. It provides reliable signal connection between the CPU and I/O modules, ensuring stable data transmission in demanding industrial automation environments. At Konmask.com, we supply both original and verified-equivalent units to support your system uptime.
Technical Specifications
- Part Number: 6ES7921-5AK20-0AA0
- Manufacturer: SIEMENS
- Product Family: SIMATIC S7-300
- Module Type: Communication / Front Connector Module
- Connection Type: Screw-type terminal
- Terminal Count: 20-pin
- Rated Voltage: 24 V DC
- Degree of Protection: IP20
- Operating Temperature: 0 °C to +60 °C
- Storage Temperature: -40 °C to +70 °C
- Dimensions (W×H×D): Refer to SIEMENS datasheet
- Weight: Approx. 100 g
- Certifications: CE, UL, cULus
Compatible Replacement & Equivalent Models
The following models are functionally compatible or serve as direct replacements for the 6ES7921-5AK20-0AA0 in most S7-300 applications. Always verify electrical and mechanical compatibility before substitution.
- 6ES7921-5AK20-0AA0 — Original SIEMENS unit (this listing)
- 6ES7921-5AH20-0AA0 — 20-pin screw-type front connector, same series, earlier revision
- 6ES7921-5BD20-0AA0 — 40-pin variant for expanded I/O modules
- 6ES7392-1AJ00-0AA0 — Alternative front connector for SM 321/322/323 modules
- 6ES7392-1BJ00-0AA0 — Spring-type terminal alternative, same pin count
Note: Cross-reference with your specific SM module datasheet to confirm pin compatibility.
Why Choose the Original Model
- ✅ Factory-tested and certified by SIEMENS for SIMATIC S7-300 systems
- ✅ Guaranteed mechanical fit with all compatible SM 300 series I/O modules
- ✅ Full traceability and SIEMENS warranty support
- ✅ Consistent screw-torque specification for reliable long-term connections
- ✅ Preferred for safety-critical and regulated industrial environments
Typical Applications
- Manufacturing automation lines (automotive, electronics assembly)
- Process control systems in chemical and pharmaceutical plants
- Building automation and HVAC control panels
- Water treatment and utilities infrastructure
- Machine tool and CNC controller integration
- Conveyor and material handling systems
System Compatibility
The 6ES7921-5AK20-0AA0 is compatible with the following SIMATIC S7-300 signal modules:
- SM 321 — Digital Input Modules
- SM 322 — Digital Output Modules
- SM 323 — Digital I/O Combination Modules
- SM 331 — Analog Input Modules
- SM 332 — Analog Output Modules
- SM 334 — Analog I/O Combination Modules
Not compatible with S7-400, S7-1200, or S7-1500 series without adapter.
Selection Guide
Use the table below to select the correct front connector for your S7-300 module:
- 20-pin screw terminal → 6ES7921-5AK20-0AA0 (this model) — for SM modules with up to 20 I/O points
- 20-pin spring terminal → 6ES7921-5AH20-0AA0 — faster wiring, tool-free connection
- 40-pin screw terminal → 6ES7921-5BD20-0AA0 — for high-density SM modules (32+ I/O)
- 40-pin spring terminal → 6ES7921-5BE20-0AA0 — high-density, tool-free
If you are unsure which connector fits your module, contact us with your SM module part number and we will confirm compatibility.
Quality Assurance & Sourcing
- 🔍 All units inspected upon receipt — visual, dimensional, and functional checks
- 📦 Original SIEMENS packaging preserved where available
- 🏭 Sourced from authorized distributors and verified secondary market channels
- 📋 Batch traceability records maintained for B2B and OEM customers
- 🚚 Ships from bonded warehouse; export documentation available on request
How to Order
- Confirm your S7-300 SM module part number (e.g., 6ES7321-1BH02-0AA0)
- Verify terminal type required: screw or spring
- Select quantity and add to cart, or contact us for bulk/OEM pricing
- For urgent requirements, email support@konmask.com with your PO details
- Lead time: In-stock items ship within 1–3 business days; special orders 5–15 days
Replacement & Compatibility FAQ
Q: Can I use 6ES7921-5AH20-0AA0 instead of 6ES7921-5AK20-0AA0?
A: Yes, both are 20-pin front connectors for S7-300 SM modules. The difference is terminal type: AK20 uses screw terminals; AH20 uses spring-clamp terminals. Electrically identical.
Q: Is this module compatible with S7-1500?
A: No. The S7-1500 uses a different backplane and front connector system. Please contact us for S7-1500 compatible parts.
Q: Do you supply new or refurbished units?
A: We supply both. New original units are available; refurbished units are clearly labeled and tested to OEM specification. Please specify your preference at checkout or via email.
Q: Can I get a certificate of conformity or test report?
A: Yes, available upon request for B2B orders. Contact support@konmask.com.
Q: What is the minimum order quantity?
A: No minimum for standard orders. Volume discounts available for 10+ units.
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