Murrelektronik 857833 Retrofit-Compatible Power Supply for Legacy Systems

Murrelektronik 857833 Retrofit-Compatible Power Supply for Legacy Systems

The Murrelektronik 857833 is a proven MPS series DIN-rail power supply engineered for seamless integration into existing automation infrastructure. As industrial facilities face mounting pressure to extend the operational life of legacy control systems while managing capital expenditure, the 857833 provides a reliable, drop-in retrofit solution for aging or discontinued power supply modules across a wide range of control cabinet configurations. Whether you are replacing an end-of-life unit in a Siemens S5 or S7 panel, upgrading a Rockwell Allen-Bradley SLC 500 control cabinet, or modernizing a Schneider Electric Modicon-based rack, the 857833 delivers stable 24 VDC output with the current capacity and form factor required for uninterrupted field operation.

Procurement engineers and maintenance teams working on brownfield automation projects consistently identify power supply compatibility as a critical gating factor during system migration. The 857833 addresses this directly: its compact DIN-rail footprint, wide-range AC input, and regulated DC output make it compatible with the majority of legacy backplane and terminal block arrangements found in control cabinets installed over the past two decades. When replacing older Murrelektronik MPS units or equivalent third-party supplies, technicians should verify output current rating, terminal pitch, and mounting depth against the existing cabinet layout before committing to installation.

Upgrade Compatibility Table

Retrofit Planning for Existing Automation Systems

Successful integration of the Murrelektronik 857833 into a brownfield control system requires a structured pre-installation review. Begin by auditing the total connected load on the 24 VDC bus: sum the current draw of all downstream devices including Murrelektronik MPS-CAP capacitor buffer modules, Murrelektronik MICO Pro electronic circuit breakers, and any third-party I/O modules or signal conditioners sharing the same rail. Overloading a replacement supply is one of the most common causes of premature failure during retrofit projects, and it is entirely preventable with a proper load calculation.

Terminal block wiring is the next critical checkpoint. Legacy cabinets often use Phoenix Contact or Weidmüller terminal strips with 5.08 mm or 7.62 mm pitch. Confirm that the 857833 terminal block pitch matches the existing wiring harness before pulling cables. Where the pitch differs, plan for a short jumper section or terminal adapter to avoid re-terminating the entire harness — a time-consuming task that extends planned downtime unnecessarily.

For systems where the 857833 feeds a Siemens S7-300 or S7-400 CPU rack, verify that the PS 307 or PS 405 power supply slot is being replaced or supplemented rather than duplicated. In many legacy S7-300 installations, the rack-mounted power supply module handles backplane power while a separate DIN-rail supply like the 857833 feeds field devices and I/O modules such as the SM 321 digital input module or SM 331 analog input module. Maintaining this separation during retrofit preserves the original system architecture and simplifies re-commissioning.

Where the control system includes a Profibus DP network, confirm that the 857833 output is clean and within ripple specification before connecting sensitive Profibus repeaters or DP/PA segment couplers. Excessive ripple on the 24 VDC bus is a known cause of intermittent Profibus communication faults that are difficult to diagnose without a power quality analyser. Similarly, for systems migrating from Profibus to Profinet, the 857833 can continue to power legacy field devices during the transition period while new Profinet-capable I/O modules such as Murrelektronik MVK Metal or equivalent distributed I/O stations are brought online progressively.

HMI panels — whether legacy Siemens OP7/OP17 operator panels or more recent Weintek or Proface touchscreens — typically draw between 0.5 A and 2 A from the 24 VDC bus. Account for this load in your power budget. Programming cables and handheld programming devices such as the Siemens MPI adapter or Profibus PC adapter also draw from the same bus during commissioning; factor in this temporary additional load when sizing the supply.

Finally, confirm available installation space in the control cabinet. The 857833 DIN-rail footprint is compact, but adjacent components — including cable ducts, terminal blocks, and existing Murrelektronik MPS series units being retained — may constrain the available slot width. A dimensioned cabinet layout drawing reviewed before ordering avoids costly on-site modifications.

Downtime Control During System Migration

Minimising unplanned downtime is the primary operational concern during any power supply replacement in a live production environment. The recommended approach for replacing the 857833 in a running system is a planned hot-swap window during a scheduled maintenance shutdown, rather than an emergency replacement under production pressure. Prepare a pre-tested spare unit — verified against the original load profile on a bench test rig — so that the swap can be completed within a single shift.

Before de-energising the cabinet, photograph or document the existing terminal wiring layout. Label every conductor at both ends if labels are missing or illegible. This step alone eliminates the majority of wiring errors during re-commissioning and protects the original PLC program logic from being corrupted by incorrect I/O connections after power restoration.

Where the process cannot tolerate a full shutdown, consider installing the 857833 in parallel with the existing supply on a separate DIN-rail section, powering non-critical field devices first while the legacy supply continues to power the PLC CPU and critical I/O. Once the 857833 is confirmed stable under partial load, transfer the remaining circuits progressively. This staged migration approach is particularly effective in continuous process industries where even a brief interruption to the control loop can trigger a costly process upset.

After restoration, perform a full I/O scan from the PLC programming terminal to confirm that all digital and analog signals are reading correctly. Check Profibus or Profinet diagnostic screens for any communication faults introduced during the power interruption. Verify HMI alarm logs for any spurious alarms generated during the transition. Document the completed retrofit in the cabinet maintenance log with the 857833 serial number, installation date, and technician sign-off to support the 12-month warranty claim if required.

Retrofit Support FAQ

Q1: Is the Murrelektronik 857833 a direct replacement for older MPS series power supplies?
The 857833 is designed within the Murrelektronik MPS series platform and shares the same DIN-rail mounting standard and 24 VDC output architecture as earlier MPS units. For specific discontinued part numbers, compare the output current rating and terminal configuration to confirm compatibility before installation. Our team can assist with cross-reference verification prior to order placement.

Q2: What commissioning checks are required after installing the 857833?
After installation, measure the output voltage at the terminal block under full load to confirm it is within the 24 VDC ±1% specification. Check the output ripple with an oscilloscope if the downstream system includes sensitive analog I/O or communication modules. Verify that all upstream fuses and circuit breakers are correctly rated for the 857833 input current. Perform a full PLC I/O scan and communication diagnostic before returning the system to production.

Q3: Can the 857833 be used alongside Murrelektronik MICO Pro circuit breakers and MPS-CAP buffer modules?
Yes. The 857833 is fully compatible with Murrelektronik MICO Pro electronic circuit breakers for selective load protection and with MPS-CAP capacitor buffer modules for bridging brief mains interruptions. This combination is a standard configuration in high-availability control cabinet designs and is supported by Murrelektronik’s system documentation.

Q4: What does the 12-month warranty cover, and is pre-shipment testing included?
Every Murrelektronik 857833 unit supplied by NINERMAS undergoes a pre-shipment functional test covering output voltage, current capacity, and thermal performance. The 12-month warranty covers manufacturing defects and functional failures under normal operating conditions from the date of shipment. Warranty claims are supported with documentation of the pre-shipment test result. Contact sale@ninermas.com for warranty registration and claim procedures.