Allen Bradley 1756-PA72 1756-PA75 1756-PB72 1756-PB75 1756-PSCA2 ControlLogix Power Supplies

The Allen-Bradley 1756 ControlLogix power supply series provides robust, regulated power to the ControlLogix chassis, supporting the entire Logix5000 architecture. Available in standard, redundant, and extended-voltage configurations-including the 1756-PA72, 1756-PA75, 1756-PB72, 1756-PB75, and 1756-PSCA2-these modules deliver consistent, reliable energy to high-performance CPUs and I/O modules. Designed for high availability and fault-tolerant environments, they ensure system uptime and deterministic operation across diverse industrial automation and SIL 3 safety applications.
We stock new Allen-Bradley 1756 power supply modules. All units are original, factory sealed, with a 1-year warranty. Whether you require a replacement to restore power redundancy or components for a new chassis build, our team can help verify system compatibility and voltage requirements before shipment.

Technical Notes:

• The discontinued 72-series (10 A max at 5.1V, 50W) can be directly replaced by the active 75-series (13 A max, 75W). Always verify that the total chassis module current draw does not exceed the power supply's maximum wattage limits.
• AC modules (1756-PA72/PA75) can draw a peak inrush current up to 30 A upon startup. Upstream circuit breakers and transformers must be sized correctly to prevent nuisance tripping during plant power-up.

• Global Regulatory Compliance: Models 1756-PA72, 1756-PA75, 1756-PB72, 1756-PB75, and 1756-PH75 meet identical industrial certification standards, including c-UL-us, CE, UKCA, ACMA (RCM), and Ex (ATEX/IECEx Zone 2) for hazardous locations. All units are approved for deployment within SIL 3 rated Functional Safety Logix5000 architectures.
• Reinforced Circuit Isolation: The 1756 power supply series features a standardized safety isolation design providing 250V continuous isolation voltage (Reinforced Insulation Type). Each module is factory type-tested at 3500V DC for 60 seconds from the primary power input to the chassis backplane.
• Dual-Tier Power Capacity: Chassis backplane power output is defined by model suffix. The 72-series (1756-PA72, 1756-PB72) delivers up to 50W total power with a 10 A maximum current limit at 5.1V DC. The 75-series (1756-PA75, 1756-PB75, 1756-PH75) increases output capacity to 75W total power with a 13 A maximum current limit at 5.1V DC.

Input Architecture & Power Source

• 1756-PA75: Operates on standard plant AC power (85–265V AC). Designed for conventional factory automation grids.
• 1756-PH75: Operates on high-voltage DC power (90–143V DC). Tailored for heavy industrial DC grids, substations, and battery-bank backup systems.

Startup Surge vs. Thermal Load

• 1756-PA75: High startup stress but runs cool. Draws up to 30 A inrush current on power-up, requiring robust upstream circuit protection, but maintains low heat dissipation (25W).
• 1756-PH75: Low startup stress but runs hotter. Limits inrush current to 20 A, but generates higher continuous thermal load (35W), requiring better enclosure ventilation.

Shared DNA

Despite opposite input requirements, both modules deliver identical 75W (13 A at 5.1V) backplane capacity, occupy the same chassis footprint, and carry identical SIL 3 and Zone 2 safety certifications.

 

Key Specs(1756-PA75)

• Input Voltage: 85–265V AC (Nominal 120V/240V AC)
• Input Frequency: 47–63 Hz
• Max Input Power: 120VA
• Output Power: 75W @ 0–60 °C
• Backplane Current Output: 13 A @ 5.1V DC, 4.0 A @ 3.3V DC, 2.8 A @ 24V DC
• Peak Inrush Current: 30 A
• Power Dissipation: 25W (85.3 BTU/hr) Max
• Isolation Voltage: 250V continuous, Reinforced Insulation Type (tested at 3500V DC for 60s)

The matrix below provides an absolute hardware breakdown of all 1756 series power Supply, including lifecycle status, backplane output ratings, and electrical consumption variables.

Product Image	Catalog Number	Product Lifecycle Status	Hardware Series	Input Voltage Range	Max Input Power	Peak Inrush Current	Action
	1756-PA72	Discontinued	Up to Series C	85–265V AC	100VA	30 A	Inquire Now!
	1756-PA75	Active	Series B	85–265V AC	120VA	30 A	Inquire Now!
	1756-PB72	Discontinued	Up to Series C	18–32V DC	95W	30 A	Inquire Now!
	1756-PB75	Active	Series B	18–32V DC	110W	30 A	Inquire Now!
	1756-PH75	Active	Series B	90–143V DC	95W	20 A	Inquire Now!

Note: The active 75-series provides an upgraded 75W backplane capacity to replace the discontinued 50W 72-series, though the 1756-PH75 variant features a restricted 24V DC output limited to 1.75 A.

Technical Notes & Application Caveats: 

• Redundant Models (-R, -PAR2): Cannot be installed directly into a standard ControlLogix chassis slot. These modules must be mounted externally and require two identical power supplies, two 1756-CPR2 (or CPR2U/CPR2D) cables, and one 1756-PSCA2 chassis adapter to establish a redundant system. Note that the legacy 1756-PAR2 does not provide 3.3V DC backplane power.
• Conformal Coated Models (-K): Feature identical electrical input and backplane output ratings to their standard counterparts.
• Extreme Environment Models (-XT: 1756-PA75XT / 1756-PB75XT): Featuring a corrosion-resistant coating and an extremely wide operating temperature range (-25°C to +70°C), these power supplies are commonly used in oil drilling platforms, mining operations, or in harsh outdoor environments.

During control system lifecycle upgrades and maintenance, chassis power capacity and backplane current allocation play a critical role in system stability. To assist engineers in evaluating hardware replacements and mitigating selection risks, the following technical matrix details the mechanical and electrical transition paths from legacy models to current active industry standards:

Replacement and maintenance core tips: When using an existing 75 series unit to replace a discontinued 72 series unit in situ, the physical installation dimensions and interfaces on Series B and Series C racks are completely identical, allowing for direct plug-and-play replacement. However, it should be noted that for special applications involving the 1756-PH75 (high-voltage DC model), its 24V DC backplane current output limit is limited to 1.75 A (while other standard 75 series units are 2.8 A). Look for "Series C" (C-series upgrade): Rockwell has been fully promoting Series C power supplies in recent years (such as the 1756-PA72 Series C or 1756-PA75 Series C). The new version optimizes internal components and features a significantly improved ventilation and heat dissipation design.Therefore, during selection and maintenance replacement, the total current consumption of modules within the rack must be strictly verified to avoid overload and system shutdown.

Backplane Current Loading & Capacity

ControlLogix power Supply distribute current to the controller and all modules via four DC voltage rails (5.1V, 3.3V, 24V, 1.2V DC) on the rack backplane. When selecting a power supply, the sum of the maximum current consumption of all modules on each rail must never exceed the power supply's maximum rated output limit.
Typical Example:

• 1756-PA72 / PB72 (Older 50W): Its 5.1V output limit is 10 A, and its 24V limit is 2.0 A, and it completely lacks 1.2V DC output capability.
• 1756-PA75 / PB75 (Current 75W): Increases the 5.1V current to 13 A and the 24V current to 2.8 A, and adds a new 1.5 A dedicated 1.2V DC power rail (to support the new generation controller).
• 1756-PH75 (High Voltage DC 75W): Although the total power is also 75W, the current of its 24V DC rail is strictly limited to 1.75A. If a large number of high-power analog or communication modules are inserted in the rack, the technical data of each module must be strictly verified during selection to avoid overloading the 24V rail.

Power Memory Retention & Ride-through

On the controller side, data retention relies on internal non-volatile memory (such as the L8 series built-in flash memory) or an external lithium battery pack. On the power supply side, the corresponding metric is "Ride-through Time," which is the time the power supply maintains uninterrupted DC power to the backplane when a brief grid dip occurs at the input.

1. AC Power Supply (1756-PA72 / PA75): The official rated transient retention time is 20 ms (at rated input voltage). When grid flicker is less than one full cycle (at 50Hz), the power supply uses internal energy storage capacitors to maintain stable backplane current; if it exceeds 20 ms, a shutdown protection signal is immediately injected into the backplane.
2. DC Power Supply (1756-PB72 / PB75): Offers stronger grid switching tolerance. The 1756-PB72 has a hold time of 30 ms, while the existing 1756-PB75 has been improved to 40 ms, which can perfectly match the hardware architecture of the controller's modern battery-free (ESM energy module).

Chassis & Hardware Compatibility

Safety Isolation & Electrical Protection Architecture

The power supply integrates independent fault detection circuitry that immediately limits output or triggers internal fuse isolation when input voltage or backplane load current exceeds safety thresholds. To guarantee absolute electrical safety, a continuous isolation capacity of 250V is maintained between the power supply input and backplane rails, backed by factory type testing requiring both AC and DC models to withstand 3500V DC for 60 seconds. Furthermore, protection extends to harsh environments via specialized hardware: models with a -K suffix feature internal conformal coating to resist corrosive gases and salt spray, while -XT extended temperature models utilize higher thermal protection thresholds to support full-load operation from -25 to +70 °C (-13 to +158 °F).

Redundant Operation & High-Availability Architecture

This section details the hardware fault-tolerance architecture at the power supply side, achieved through the collaboration of dual power supplies, interconnect cables, and a chassis adapter.

• External Decoupled Physical Architecture (External Routing): Official redundant power supplies (such as the 1756-PA75R/PB75R) are strictly prohibited from-and physically incapable of-being directly inserted into standard chassis slots. The system must consist of two redundant power supplies, two dedicated 1756-CPR2 interconnect cables, and a 1756-PSCA2 chassis adapter installed on the leftmost side of the chassis.
• Current-Sharing Mechanism: When both power supplies are online under normal operating conditions, they execute hardware-level parallel operation via the interconnect cables. The system does not operate in a passive "primary/standby" state; instead, each unit actively balances and supplies approximately 50% of the total backplane load current.
• Bumpless Transfer & Hot-Swapping: If a single power supply experiences a power loss or internal hardware failure, the remaining unit automatically executes a bumpless transfer within microseconds to independently assume 100% of the load. This seamless transition prevents backplane voltage drops from triggering a controller firmware reset.

Pre-installation Requirements & Safety Guidelines

Before performing any physical operations, the following safety announcements from the official manual must be strictly verified and observed:
SHOCK HAZARD: Disconnect all input power sources before installing, wiring, or removing the power supply module.
EXPLOSION HAZARD:

• This equipment is certified for use only in Class I, Division 2, Groups A, B, C, D hazardous locations.
• Do not disconnect equipment or perform any wiring/operations unless power has been switched off or the area is known to be nonhazardous.

Electrostatic Discharge (ESD) Protection: This equipment contains components sensitive to electrostatic discharge. Wear a grounded wrist strap when handling the module, and do not touch the backplane connector pins.

Mechanical Installation Steps

The ControlLogix power supply must be installed into the leftmost slot of the 1756 chassis. The installation sequence must be executed exactly as follows:
Align the Guides: Line up the circuit board (P1 connector side) on the rear left of the power supply with the top and bottom card guides on the far left of the chassis frame.
Slide and Engage: Flushly push the power supply module backward.

• Standard Power Supplies: Push firmly until the locking tabs at the top and the positioning pins at the bottom of the module fully engage with the chassis.
• Redundant Power Supplies (if applicable): Ensure that the dedicated chassis cable (1756-CPR2) has been properly connected beforehand.

Screw Fastening: Using a Phillips screwdriver, tighten the two mounting screws at the top and bottom of the power supply module.

• Rigorous Requirement: The screws must be fully tightened to ensure long-term, reliable grounding continuity between the power supply and the chassis frame.

Electrical Wiring Specifications & Terminal Definitions

Before wiring, verify the terminal block functions based on the specific model (AC or DC). All operations must meet the following technical criteria:

Wire & Torque Specifications

1. Wire Size: Must use 2.5 mm² (14 AWG) solid or stranded copper wire.
2. Temperature Rating: The wire insulation temperature rating must not be less than 90 °C (194 °F).
3. Strip Length: Maximum insulation strip length is 11 mm (0.44 in.).
4. Tightening Torque: Terminal screws must be torqued to 0.8 N·m (7 lb·in).

Terminal Strip Pin Definitions

⚠️ Special Warnings:

• Do not use jumper strips in external wiring to bridge terminals.
• The chassis ground stud itself must be connected to the Protective Earth (PE) bus of the control cabinet using a copper wire no smaller than 5.3 mm² (10 AWG) via the shortest path possible.

Commissioning Critical Step: Removing the Protective Label

This is a critical procedure highlighted with a WARNING level in the official manual and must be executed before applying power:

1. Locate the Label: Find the yellow or transparent protective label covering the ventilation slots on the top of the power supply.
2. Peel-Off Operation: After all drilling, wiring, and cleaning inside the control cabinet are completed, and prior to applying power, the label must be completely removed manually.
3. Technical Principle: This label is intended solely to prevent metal debris or stray wire strands from falling inside the module during installation. Failing to remove the label before applying power completely blocks air convection, causing rapid heat accumulation that triggers the internal thermal cut-out or damages components.

Power-Up Status Verification (LED Indicators)

After confirming the protective label is removed and the chassis is clear of debris, close the main power supply switch and strictly verify the status using the "POWER" LED on the front panel:

• Solid Green: Indicates the power supply is operating normally. All DC voltages required by the backplane (1.2V, 3.3V, 5.1V, 24V DC) are within their legal, standard thresholds.
• LED Off: Power must be disconnected immediately. Check whether the input voltage is missing, polarities are reversed, or if there is a severe overload/short circuit caused by modules on the backplane.

When a system failure occurs, diagnostics begin with verifying the front-panel LED status, followed by a systematic module-isolation process if a backplane fault is detected.
LED Status Assessment:

• Solid Green: System normal; all backplane voltages are within specification.
• LED Off: No input power, or out-of-range input voltage. Check breakers and measure terminal voltage; if input power is good, the internal fuse is blown and the module requires replacement.
• Blinking Green: Backplane short-circuit, overload, or thermal cut-out (often caused by blocked vents or an unremoved protective label). Clear obstructions and initiate fault isolation.

Step-by-Step Fault Isolation

1. Disconnect Power: Turn off the main incoming AC or DC power source.
2. Strip Chassis: Remove all controller, communication, and I/O modules, leaving only the power supply in Slot 0.
3. Test Supply: Turn power on. If the LED blinks or stays off, the power supply or chassis is defective-replace the power supply. If the LED turns solid green, the supply is functional; proceed to step 4.
4. Isolate Module: Turn power off, re-insert one module, and turn power back on to check the LED.
5. Identify Fault: Repeat the "Power Off --> Insert --> Power On" cycle for each module. The specific module that triggers a blinking or dead LED houses the internal short circuit and must be replaced.

Safety and Maintenance Rules
Explosion Hazard: Never plug or unplug modules while the chassis is energized in Class I, Division 2 hazardous locations to prevent electrical arcing.
Thermal Reset: After a thermal shutdown, turn off input power and allow the module to cool for 10 to 15 minutes before restarting.
No Field Repairs: Internal components and fuses are non-serviceable. Opening the housing voids safety certifications; faulty units must be completely replaced.

We stock the following 1756 Power Supply models (new, factory sealed):

1756-PAR2, 1756-PA72, 1756-PA75R, 1756-PA75, 1756-PB72, 1756-PB75R, 1756-PB75, 1756-PH75, 1756-PSCA2...

All units include:

• Original Allen-Bradley packaging
• Clear product status report (date code, firmware version if available)
• 1-year warranty

Lead time: Same-day processing for in-stock items. Shipping via DHL, UPS, or FedEx.

Contact now

ControlLogix power supplies are consistently bundled with chassis. When customers search for these power supplies, they are highly likely expanding or maintaining their rack systems. If you need the complementary items like the 1756-A10 (10-slot chassis), 1756-A17 (17-slot chassis), or CPU processors such as the 1756-L73 and 1756-L81E. please contact Vicky.

Need help verifying firmware compatibility or safety certification requirements?

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