The Allen-Bradley 1756-PA75R, also cataloged as the 1756PA75R ControlLogix AC Redundant Power Supply, operates as a dedicated hardware component for delivering 75 W regulated DC backplane power within ControlLogix chassis architectures.

Catalog Number Matrix

The suffix "R" appended to the base 1756-PA75 model explicitly designates redundant power supply operation. This configuration mandates paired installation with a second identical module within the same chassis to achieve seamless power bus switching. The base part number 1756PA75R serves as the internal logistics identifier.

Electrical & Mechanical Data

Backplane Bus Communication & Firmware Flash Compatibility

The 1756-PA75R interfaces directly with the 1756 ControlLogix backplane to monitor internal thermal status and report fault conditions to the processor via system status words. Firmware flash compatibility is strictly governed by the installed ControlLogix major revision. Mixing modules with incompatible firmware revisions on the same redundant power bus may result in synchronization loss during primary-to-standby transitions. The module does not support user-accessible firmware downgrades below the factory-shipped revision level.

Ordering Information

• 1 x 1756-PA75R AC Redundant Power Supply module
• 1 x Installation instruction sheet (publication 1756-IN...)
• 1 x Removable terminal block (if applicable to chassis configuration)

Chassis Integration & Wiring Guidelines

• Rack Positioning: Install the primary and redundant modules in the designated left-most power slots (slots 0 and 1) of a 1756 ControlLogix chassis. Do not install standard (non-redundant) power supplies in the companion slot.
• AC Mains Isolation: Maintain minimum 75 mm separation between AC input wiring and low-voltage DC backplane wiring to prevent inductive coupling and electromagnetic interference.
• Grounding: Connect the chassis ground lug to a verified earth ground point using 14 AWG or larger copper conductor. Do not rely solely on DIN rail or panel mounting for safety grounding.
• Inrush Consideration: The 20 A inrush current at power-up may trip upstream circuit breakers rated below 30 A. Size branch circuit protection accordingly.

Frequently Asked Questions

Does the 1756-PA75R support hot-swap removal under load?

Yes. The module supports online removal and insertion (ORI) when installed as part of a redundant pair. The standby module assumes the full backplane load within the chassis transfer time, preventing system shutdown. Always verify the companion module is in RUN status before extracting the primary unit.

What is the backplane current consumption of this supply?

The 1756-PA75R does not draw current from the backplane; it sources power to the backplane. Total backplane current available depends on the chassis model. The 75 W output rating limits the cumulative module load to approximately 3 A at 24 VDC equivalent across all installed I/O modules.

Can a 1756-PA75R operate standalone without a redundant partner?

No. The "R" suffix designates redundant architecture. Standalone operation requires the non-redundant 1756-PA75 model. Installing a single 1756-PA75R without a companion module will result in a fault indication and the module will not energize the backplane.

What is the maximum allowable ambient temperature for full 75 W output?

The module delivers 75 W continuously at 60 deg C. Above 60 deg C, output derates linearly. At 70 deg C, output capability drops to approximately 60 W. Refer to the installation manual for the exact derating curve.

Is the 1756-PA75R compatible with 1756-L8x processors?

Yes. The 1756-PA75R is compatible with all 1756 chassis types and processor generations, including GuardLogix L8x series. Verify chassis slot keying matches the module mechanical profile before insertion.

What input protection does the module provide against voltage transients?

The module incorporates internal metal-oxide varistor (MOV) clamping on the AC input stage. For environments with frequent lightning or switching surges, external surge suppression devices rated for 275 VAC should be installed upstream of the module disconnect switch.

How is redundant switching failure diagnosed?

The module front-panel LEDs indicate REDUNDANT OK, ACTIVE, and FAULT statuses. A solid REDUNDANT OK LED confirms synchronization with the companion module. If the LED flashes, backplane communication between the two supplies is interrupted; check for physical module seating and chassis backplane integrity.

Can the input voltage range accept 277 VAC?

No. The absolute maximum input range is 85-265 VAC. Applying 277 VAC exceeds the module's input stage rating and will cause immediate internal fuse blow or component destruction. For 277 VAC applications, use a step-down transformer or external power conversion.