SIEMENS 6ES5951-7LD21 Power Supply PS951 7/15A | Replacement, Equivalent & Selection Guide
The SIEMENS 6ES5951-7LD21 is a dedicated power supply module (PS951) for the SIMATIC S5 PLC series, delivering 5 VDC / 7 A and 24 VDC / 15 A outputs. This page provides full technical specifications, verified compatible replacements, application guidance, and sourcing assurance for industrial automation engineers and procurement teams.
Technical Specifications
- Part Number: 6ES5951-7LD21
- Series: SIMATIC S5 – PS951
- Output 1: 5 VDC / 7 A (logic supply)
- Output 2: 24 VDC / 15 A (load supply)
- Input Voltage: 120/230 VAC, 50/60 Hz (auto-ranging)
- Form Factor: Rack-mount module for S5-115U / S5-135U / S5-155U
- Protection Class: IP20
- Operating Temperature: 0 °C to +60 °C
- Weight: approx. 2.0 kg
- Manufacturer: Siemens AG, Germany
Compatible Replacement & Equivalent Models
When the original 6ES5951-7LD21 is unavailable or end-of-life, the following models are commonly evaluated as replacements. Always verify electrical and mechanical compatibility before substitution:
- 6ES5951-7LB21 – PS951 5 VDC / 5 A variant; suitable for lighter-load S5 racks
- 6ES5951-7LC21 – PS951 5 VDC / 7 A + 24 VDC / 10 A; reduced 24 V capacity
- 6ES5951-7ND21 – Wide-range input version; preferred for unstable grid environments
- 6ES5955-3LC41 – PS955 series; compatible with S5-115U extended racks
- Third-party equivalents – Must match 5 V / 7 A + 24 V / 15 A output, S5 backplane connector pinout, and CE/UL certification
Note: Siemens SIMATIC S5 is a discontinued platform. Siemens recommends migration to S7-300/S7-1500 for new projects. Contact us for migration assessment support.
Why Choose the Original Model
- Guaranteed compatibility with all S5-115U, S5-135U, and S5-155U rack configurations
- Proven field reliability in continuous 24/7 industrial environments
- Dual-output design eliminates the need for a separate 24 V auxiliary supply
- OEM-certified – no firmware or hardware adaptation required
- Reduced commissioning risk for legacy plant maintenance and brownfield upgrades
Typical Applications
- Legacy SIMATIC S5 PLC rack power restoration and spare-parts stocking
- Automotive assembly line control systems (body shop, paint shop)
- Chemical and petrochemical process control panels
- Water treatment and utilities SCADA infrastructure
- Steel mill and heavy-industry drive control cabinets
- Brownfield plant maintenance where S5 → S7 migration is deferred
System Compatibility
- SIMATIC S5-115U (6ES5115-3UA11, 3UA12, 3UA13)
- SIMATIC S5-135U (6ES5135-3UA11, 3UA12)
- SIMATIC S5-155U (6ES5155-3UA11, 3UA12)
- Compatible with all standard S5 I/O modules: digital, analog, communication, and positioning
- Not compatible with SIMATIC S5-90U / S5-95U (different form factor)
Selection Guide
Use the table below to select the correct PS951 variant for your rack configuration:
- 5 V load ≤ 5 A, 24 V load ≤ 10 A → 6ES5951-7LB21
- 5 V load ≤ 7 A, 24 V load ≤ 10 A → 6ES5951-7LC21
- 5 V load ≤ 7 A, 24 V load ≤ 15 A → 6ES5951-7LD21 ✓ (this model)
- Unstable AC input / wide-range grid → 6ES5951-7ND21
- Extended rack / high I/O count → 6ES5955-3LC41 (PS955 series)
If unsure about your rack’s actual power consumption, contact our engineering team for a free load calculation review.
Quality Assurance & Sourcing
- All units sourced from authorized distributors or verified surplus channels
- Pre-shipment inspection: visual, dimensional, and functional power-on test
- Authenticity verification: label, date code, and PCB markings cross-checked
- Packaging: anti-static bag + foam-lined carton with humidity indicator
- Documentation available: test report, certificate of conformity (CoC), and packing list
- Warranty: 12 months from shipment date against manufacturing defects
How to Order
- Step 1: Confirm your rack model and current power consumption (5 V and 24 V rails)
- Step 2: Verify quantity required and lead-time expectations
- Step 3: Submit your RFQ via [email protected] or add to cart directly
- Step 4: Receive proforma invoice with stock confirmation within 24 business hours
- Step 5: Payment → inspection → shipment with full tracking
Bulk orders (5+ units) qualify for priority allocation and volume pricing. Contact us for a quote.
Replacement & Compatibility FAQ
Q: Can I use 6ES5951-7LC21 instead of 6ES5951-7LD21?
A: Yes, if your 24 VDC load does not exceed 10 A. The -7LD21 provides 15 A on the 24 V rail; the -7LC21 is limited to 10 A. Exceeding this will trigger overcurrent protection.
Q: Is 6ES5951-7LD21 compatible with S5-90U?
A: No. The S5-90U uses a different compact rack format. This module is designed for the U-series central racks (115U / 135U / 155U) only.
Q: Can this power supply be repaired instead of replaced?
A: Board-level repair is possible for common failures (capacitor aging, rectifier diodes). We offer repair assessment on request. However, for critical production environments, replacement is recommended for reliability.
Q: Do you provide a migration path to SIMATIC S7?
A: Yes. We can advise on S5 → S7-300 or S7-1500 migration, including I/O mapping, program conversion tools (STEP 5 → STEP 7 / TIA Portal), and hardware BOM.
Q: What is the typical lead time?
A: In-stock units ship within 3–5 business days. Out-of-stock items are sourced within 2–4 weeks depending on global availability.
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