Product Overview

The Allen-Bradley 1756-PA75R​ is a 75-watt redundant AC input power supply module engineered for Rockwell Automation ControlLogix® 1756 series programmable automation controller (PAC) chassis. Designed to occupy the left-most slot(s) of a standard 1756 chassis (such as 1756-A7, 1756-A10, 1756-A13, or 1756-A17), the 1756-PA75R​ converts a wide-range 85–265 V AC single-phase mains supply (47–63 Hz) into the multiple regulated DC voltages required by the ControlLogix backplane: 5.1 V DC for logic, 3.3 V DC and 1.2 V DC for processor support, and 24 V DC for local I/O module auxiliary power. Its defining characteristic—distinguishing it from the non-redundant 1756-PA75—is its ability to operate in an N+1 redundant configuration when two units are installed with a 1756-PSCA2 Redundancy Adapter/Cable Kit, providing automatic current sharing and seamless failover in the event one supply fails or is removed for maintenance.The Allen-Bradley 1756-PA75R​ is the recommended power solution for continuous-process and mission-critical applications where unplanned downtime due to a single power supply failure cannot be tolerated. When deployed as a redundant pair, both supplies actively share the load (approximately 50/50), and if one unit loses AC input or develops an internal fault, the remaining unit instantly assumes the full backplane load without interruption to the processor, I/O scan, or network communications. A built-in DC OK status relay contact (Form C, isolated) and multifunction LEDs (PWR, FLT) provide local and remote indication of supply health, enabling integration into plant-wide alarm and diagnostic systems. The module is convection-cooled with an internal fan for thermal management and is hot-swappable when the chassis is properly configured with the redundancy adapter—allowing replacement of a faulty 1756-PA75R​ without powering down the control system, a capability that is fundamental to achieving high availability in industries such as oil & gas, power generation, pharmaceuticals, and large-scale continuous batch processing.Fully compatible with all 1756-series processors (ControlLogix 5550, 5560, 5570, 5580 families), communication modules, and I/O—provided the total backplane and I/O module current draw does not exceed the supply’s rated capacity—the 1756-PA75R​ represents Rockwell Automation’s standard redundant power option for mid-size ControlLogix installations requiring proven, UL-listed, CE-compliant redundant power architecture.

Technical Specifications

Product Model | 1756-PA75R​ (also referenced as 1756-PA75R Series A / 1756-PA75R/A)Manufacturer | Allen-Bradley / Rockwell AutomationProduct Type | ControlLogix 75W Redundant AC Input Power Supply ModuleInput Voltage | 85–265 V AC, Single Phase, 47–63 Hz (auto-ranging universal input)Input Current (full load) | 1.5 A @ 120 V AC; 0.8 A @ 230 V AC (typical)Inrush Current | < 30 A peak, < 1 ms durationOutput Power (Total) | 75 W maximum @ 60 °C (derates above 60 °C to 50 W @ 70 °C)Backplane Logic Output | 5.1 V DC ±1%, 13 A max (66 W)Auxiliary Outputs | 3.3 V DC @ 4 A max; 1.2 V DC @ 1.5 A max; 24 V DC @ 2.8 A max (67 W combined aux limit)Hold-up Time | ≥ 2 AC line cycles (≥ 20 ms @ 120 V AC, ≥ 40 ms @ 230 V AC) at full loadRedundancy Support | Yes — N+1 parallel redundant operation with second 1756-PA75R + 1756-PSCA2 adapter & 1756-CPR2 cableIsolation | 250 V AC (Input to Chassis Ground / Backplane); 50 V DC (Outputs to Input)Status Indication | PWR (Green = DC outputs healthy), FLT (Red = fault detected), DC OK Relay (Form C, 30 V DC / 1 A, isolated)Operating Temperature | 0 °C to +60 °C (32 °F to 140 °F), derated above 60 °CDimensions (H×W×D) | 157 × 152 × 140 mm (6.18 × 5.98 × 5.51 in) — occupies 1 left-most chassis slotWeight | Approx. 1.45 kg (3.2 lb)Cooling Method | Convection with internal temperature-controlled fanCertifications | cULus Listed, CE, C-Tick, FM Class I Div 2 Groups A,B,C,D, ABS (Marine Type Approval where applicable)Required Chassis | Any 1756 ControlLogix chassis (1756-A4, A7, A10, A13, A17) with 1756-PSCA2 for redundancy

Main Features and Advantages

N+1 redundant operation with automatic load sharing: The primary differentiator of the 1756-PA75R​ versus the standard 1756-PA75 is its redundant-ready design. Two units installed in a chassis equipped with the 1756-PSCA2 Redundancy Adapter and interconnected via 1756-CPR2 cables actively share output current in proportion to their capacity. If one supply fails, is switched off, or is physically removed (hot-swapped), the surviving unit immediately picks up 100 % of the load with no glitch on the 5 V or 24 V rails—preserving processor operation, I/O state, and network communications. This eliminates the control system power supply as a single point of failure (SPOF) in critical process control architectures.Wide-range universal AC input: The 1756-PA75R​ accepts any single-phase AC mains voltage from 85 V to 265 V across the 47–63 Hz range without manual voltage selection or jumpers. This makes it globally deployable—whether the site provides 100 V AC (Japan), 120 V AC (North America), 208 V AC (industrial 3-phase leg), 230 V AC (Europe/Asia), or 240 V AC—simplifying spare-parts inventory for multinational OEMs and reducing commissioning errors related to incorrect input voltage setting.Robust output capacity for typical ControlLogix loads: With 13 A on the 5.1 V logic rail and 2.8 A on the 24 V auxiliary rail, the 1756-PA75R​ can power a modest-to-medium ControlLogix system—typically one processor (e.g., 1756-L73), several communication modules (EN2T, DN2, etc.), and a mix of local I/O modules—within the 75 W total envelope. For larger systems exceeding this capacity, Rockwell offers the 1756-PA72 (72W) or 1756-PB75R (DC input redundant) options; however, the 75W rating of the 1756-PA75R​ is sufficient for the majority of standalone or cell-level redundant ControlLogix applications.Integrated diagnostics and remote alarm capability: The module provides a normally-closed/normally-open Form C relay contact rated 30 V DC / 1 A, which transitions on loss of DC OK (input failure, overtemperature, or output fault). This contact can be wired to a PLC digital input, annunciator panel, or DCS alarm point to provide early warning of an impending redundancy loss (e.g., one of two supplies has failed). Front-panel LEDs for Power (green) and Fault (red/amber) give immediate visual confirmation of supply status during cabinet walkthroughs.Hot-swappable in redundant configuration: When the chassis is set up with the 1756-PSCA2 redundancy adapter and at least one supply remains operational, a failed 1756-PA75R​ can be unlatched, withdrawn, and replaced with a new unit—all while the ControlLogix system remains powered and running. The replacement supply automatically initializes, synchronizes its load-share bus with the companion unit, and resumes proportional current sharing. This “no-down-time” replacement is a cornerstone requirement for plants targeting high availability and reduced mean time to repair (MTTR).

Application Field

The Allen-Bradley 1756-PA75R​ is specified wherever ControlLogix-based control systems must achieve high availability and cannot tolerate an unplanned shutdown due to a single power supply failure. In continuous-process industries—oil refineries, petrochemical plants, pharmaceutical batch facilities, and pulp & paper mills—the redundant pair of 1756-PA75R​ supplies protects the process control loop (reactor temperature control, blend ratio management, boiler combustion control, etc.) from power-related outages. Here, a single power supply failure would otherwise force a process trip, potentially costing tens of thousands of dollars per hour in lost production and creating safety hazards during restart.In power generation and water/wastewater treatment, the 1756-PA75R​ redundantly powers ControlLogix racks that supervise turbine governor interfaces, SCADA remote terminal units (RTUs), and pump station logic. Its ability to be hot-swapped is particularly valued during annual preventative maintenance outages, where one supply in each redundant pair can be deliberately de-energized, removed, tested, and replaced while the partner unit continues to power the live control system—avoiding any interruption to the treatment process or grid-connected generation control.OEMs of large packaging lines, bottling plants, and material handling systems also adopt the 1756-PA75R​ for their flagship machines where customer uptime guarantees are contractually mandated. By documenting the redundant power architecture in the machine’s electrical bill of materials and training customer maintenance staff on the LED diagnostics and hot-swap procedure, OEMs reduce field service calls related to “controller lost power” incidents. In all these scenarios, the 1756-PA75R​ delivers peace of mind through proven N+1 redundancy, global AC input compatibility, and seamless integration into the Rockwell Automation ControlLogix ecosystem.