Murrelektronik 857781 MPS 24VDC DIN Rail Power Supply Upgrade

Product Overview

Murrelektronik 857781 MPS 24VDC DIN Rail Power Supply Upgrade: Seamless Transition from Legacy Systems

The Murrelektronik 857781 is a proven MPS-series 24 VDC DIN rail power supply engineered for demanding industrial control environments. Whether you are retiring an aging Siemens SITOP PSU100S, replacing a Phoenix Contact QUINT-PS, or decommissioning an obsolete Puls PIANO series unit, the 857781 delivers a drop-in upgrade path that preserves your existing cabinet layout, wiring topology, and PLC power architecture without requiring a full system redesign.

Facilities running Siemens S7-300 or S7-400 PLCs with legacy 24 VDC bus power arrangements will find the 857781 particularly well-suited. Its regulated 24 VDC output is fully compatible with standard 24 V I/O modules, distributed I/O racks, and field device loops. Engineers migrating from older Murrelektronik MPS 10A or MPS 20A variants can retain the same DIN rail footprint and terminal block wiring, reducing retrofit labor and eliminating the need for new cable schedules.

For control cabinets housing Beckhoff CX or EK series EtherCAT couplers, Allen-Bradley 1756 ControlLogix chassis, or Schneider Electric Modicon M340 racks, the 857781 provides a stable, low-ripple DC bus that meets the strict power quality requirements of high-speed digital I/O and fieldbus communication modules. Its wide-range AC input accepts 100–240 VAC, making it equally suitable for domestic 220 V installations and export-market 110 V panels without hardware modification.

Compatibility Comparison Table

Seamless Upgrade Solutions

A successful power supply migration rarely involves a single component. When upgrading to the Murrelektronik 857781, field engineers typically address the surrounding power distribution and signal infrastructure in the same service window to avoid repeat downtime.

On the AC input side, existing surge protection devices and EMC line filters — such as Murrelektronik MF series line filters or equivalent Schaffner FN series units — can be retained if their current ratings are compatible. The 857781’s wide-range input simplifies integration with existing transformer-fed panels.

On the DC output side, the 857781 feeds directly into 24 VDC distribution bus bars or Murrelektronik MICO Pro electronic circuit breakers, which provide per-channel overcurrent protection for individual PLC I/O segments, sensor loops, and actuator circuits. Replacing aging fuse-based distribution with MICO Pro modules during the same retrofit eliminates nuisance tripping and provides diagnostic feedback to the control system.

For installations using Siemens ET 200SP or ET 200M distributed I/O, the 857781 supplies the 24 VDC load voltage rail that powers both the IM interface module and the I/O module backplane. Engineers migrating from a Siemens SITOP PSU100S 10A to the 857781 will find the terminal layout and DIN rail position nearly identical, allowing the existing cable harness to be reused with minimal re-termination.

In Profibus DP or PROFINET architectures, the power supply stability directly affects communication reliability. The 857781’s low output ripple and fast transient response ensure that Profibus DP repeaters, PROFINET switches, and gateway modules — such as the Murrelektronik MVK Metal or Wago 750-352 Profibus coupler — maintain stable bus voltage during load switching events caused by solenoid valves or motor starters.

Where cabinet space is constrained, the 857781’s compact MPS-series housing allows it to be installed alongside Phoenix Contact CLIPLINE terminal blocks, Weidmüller WDU series terminals, and standard 4 mm² DIN rail grounding assemblies without requiring additional rail space. This is particularly valuable in retrofit projects where the original cabinet was designed around a larger, older power supply and free rail space is limited.

For applications requiring redundant 24 VDC supply — common in safety-rated SIL 2 panels or high-availability process control systems — the 857781 can be paired with a Murrelektronik redundancy module or equivalent OR-ing diode assembly to create a 1+1 redundant power architecture, protecting against single-point power failure without modifying the downstream PLC or I/O wiring.

Retrofit Guidance FAQ

Q: Can I reuse existing wiring when replacing my old 24 VDC power supply with the 857781?
A: In most cases, yes. The 857781 uses standard screw-cage terminals compatible with 0.5–6 mm² conductors. Verify that existing wire ferrules and lug sizes match the terminal pitch before re-terminating. No rewiring of the DC output distribution is required if the load current remains within the 857781’s rated output.

Q: Is the 857781 compatible with Siemens S7-300 and S7-400 PLC power requirements?
A: Yes. Both S7-300 CPU modules and S7-400 PS 407 power supply slots accept 24 VDC auxiliary input from an external supply. The 857781’s regulated 24 VDC output meets the voltage tolerance and ripple specifications required by Siemens S7 series hardware.

Q: Will the DC OK relay output interface with my existing PLC digital input?
A: The 857781’s DC OK relay provides a potential-free contact that can be wired directly to a standard 24 VDC digital input on any PLC platform, including Siemens, Allen-Bradley, Mitsubishi, and Omron systems. No additional signal conditioning is required.

Q: How do I handle the physical space difference if the 857781 is narrower than my old unit?
A: Use standard DIN rail end stops and spacer clips to secure the 857781 in position. If the vacated rail space is significant, fill with blank cover modules or relocate adjacent terminal blocks to maintain a tidy, vibration-resistant installation.

Q: Does the 857781 support parallel operation for increased output current?
A: Parallel operation of switched-mode power supplies requires active current-sharing circuitry. For higher current demands, use a single higher-rated MPS unit or implement a redundancy module rather than paralleling two 857781 units directly.

Q: What communication protocols does the 857781 support for remote monitoring?
A: The 857781 provides a hardware DC OK relay signal only. For network-based power monitoring (PROFINET, EtherNet/IP, or Modbus TCP), pair the 857781 with a compatible power monitoring gateway or use a MICO Pro electronic circuit breaker module that supports fieldbus diagnostics.

Warranty Assurance

Every Murrelektronik 857781 unit shipped by TOPNLMS is covered by a 12-month warranty from the date of delivery. Prior to dispatch, each unit undergoes output voltage verification, load regulation testing, and visual inspection to confirm it meets Murrelektronik factory specifications.

If a unit exhibits any defect in materials or workmanship within the warranty period, TOPNLMS will arrange replacement or repair at no additional cost to the buyer. Our after-sales response target is within 24 business hours of a warranty claim submission. Replacement units are dispatched from our Xiamen warehouse with priority shipping to minimize your system downtime.

For procurement teams requiring documentation, we provide a test report, packing list, and commercial invoice with each shipment. Export packaging is designed to withstand international freight handling, with anti-static protection and foam cushioning appropriate for sensitive power electronics.

TOPNLMS maintains stock of the 857781 and related MPS-series components to support both immediate replacement orders and planned maintenance schedules. Contact our technical sales team to confirm current stock levels, lead times, and volume pricing for MRO or project-based procurement.