Why the 1756-PA72/C Matters in a ControlLogix Chassis
The 1756-PA72/C is an AC power supply module from the Allen-Bradley ControlLogix / Bulletin 1756 series. It converts 85-265 VAC input (nominal 120/240 VAC) into the regulated DC rails that every module in a 1756 chassis depends on. Without a healthy supply in the left slot, the backplane goes dark and the whole rack stops. That single point of dependency is why buyers treat this part as a critical spare rather than an afterthought.
What the 1756-PA72/C Actually Delivers
This is a standard ControlLogix AC supply, not a redundant or high-capacity variant. Its job is straightforward: take plant AC power and produce the low-voltage rails the chassis needs. The module provides 5 V DC at 10 A, 3.3 V DC at 4 A, 1.2 V DC at 1.5 A, and 24 V DC at 2.8 A. Total output is 75 W maximum. Isolation is rated at 250 V. The operating range is 0-60 C, matching the ControlLogix family specification of 0 to 60 C (32 to 140 F).
Key Parameters at a Glance
| Specification | Value |
|---|---|
| AC input | 85-265 VAC (nom 120/240) |
| 5 V DC output | 10 A |
| 3.3 V DC output | 4 A |
| 1.2 V DC output | 1.5 A |
| 24 V DC output | 2.8 A |
| Maximum power | 75 W |
| Isolation | 250 V |
| Operating temperature | 0-60 C |
| Mounting position | Chassis left slot |
Reading the Specs Like a Buyer
The 85-265 VAC input window is the headline. It means the same module works on nominal 120 VAC or 240 VAC feeds without a jumper change, which simplifies spares planning across plants with different supply voltages. The 75 W ceiling sets the practical limit on how many modules you can populate in one chassis. If your rack is heavily loaded with analog and communication cards, power budget becomes the deciding factor, not slot count.
The 24 V DC Rail Deserves Attention
The 2.8 A at 24 V DC output is often what field devices and certain modules draw on. When a chassis behaves erratically, the 24 V rail is a common place to start checking. The 5 V DC at 10 A rail carries the bulk of backplane logic power, while 3.3 V DC at 4 A and 1.2 V DC at 1.5 A support the lower-voltage logic on modern modules.
Where This Module Fits
ControlLogix chassis appear across oil and gas, water treatment, and heavy manufacturing. A gas compression station running a ControlLogix rack for compressor control depends on the 1756-PA72/C to keep the backplane alive. A pipeline pump station with mixed I/O and communication modules relies on the same supply. In each case, the failure mode is identical: the rack loses power and the process stops. That is why fast-dispatch spares matter more than the purchase price. Oil AutoTech focuses on exactly this need, keeping practical, ready-to-ship stock for oil, gas, and industrial automation applications.
Installation and Slot Placement
The 1756-PA72/C mounts in the left slot of a 1756 chassis. That position is not optional; the chassis backplane expects the power supply there. The ControlLogix architecture lets you place I/O and function modules in any remaining slot, so the supply position is the one fixed point in the rack. Before installation, confirm the chassis is de-energized and follow the manufacturer’s installation documentation. Verify your AC feed falls within the 85-265 VAC window and that the total module load stays under the 75 W ceiling.
Compatibility and Integration
The supply feeds the ControlLogix backplane (ControlBus), the high-speed path between modules. Chassis-based communication modules in the same rack support EtherNet/IP, ControlNet, DeviceNet, and DH+/Remote I/O. Configuration and programming happen in Studio 5000 Logix Designer (formerly RSLogix 5000). When integrating into a fieldbus network, wiring may require an external gateway or connection module; confirm cables and gateways with your supplier before commissioning.
Maintenance and Reliability
Power supplies are wear items. Heat and continuous load shorten their life. Keep the chassis airflow clear, respect the 0-60 C operating range, and inspect the supply periodically for signs of stress. In a ControlLogix rack, a spare 1756-PA72/C on the shelf is cheaper than a stopped line. That is the ROI case: one module, one slot, and the difference between a planned swap and an unplanned outage.
Selection Checklist
Before ordering, confirm the part number, the chassis model, and your total power budget. Check that your AC supply falls within 85-265 VAC and that your module count stays within the 75 W limit. The product is active, with no discontinuation date and no replacement listed. ControlLogix remains an active platform. Contact Oil AutoTech today for pricing and availability, and for hands-on help matching the right supply to your rack.
Frequently Asked Questions
Is the 1756-PA72/C still an active product?
Yes. The data lists it as active with no discontinuation date and no replacement. ControlLogix remains an active platform.
What input voltage does it accept?
It accepts 85-265 VAC, with nominal 120/240 VAC.
How much power does it provide?
It delivers 75 W maximum across its DC outputs.
Where does it mount?
It mounts in the left slot of a 1756 ControlLogix chassis.
What software configures the chassis?
Studio 5000 Logix Designer, formerly RSLogix 5000.
