Allen-Bradley 1756-PA72 — ControlLogix Power Supply Buying Guide

By Abdullah Zahid
14 min read
Allen-Bradley 1756-PA72 ControlLogix AC power supply module installed in 1756 chassis left slot

Allen-Bradley 1756-PA72 ControlLogix AC Power Supply: Specs, Pricing and Best Alternatives

Controls engineers specifying or replacing power hardware for a ControlLogix system typically arrive at the Allen-Bradley 1756-PA72 after checking two things: whether AC mains is available at the panel, and whether 75 W of combined backplane output is enough for the chassis load. This module converts 85…265 V AC input at 47…63 Hz into three regulated DC backplane rails — 5.1 V DC at 10 A, 3.3 V DC at 4 A, and 24 V DC at 2.8 A — and mounts on the left side of any 1756 ControlLogix chassis, powering all installed modules in that chassis only.

If you have already confirmed this is the correct part for your project, check current pricing and availability for the 1756-PA72 at LeadTime.ca — we ship worldwide.

Who Should Buy the 1756-PA72 — and Who Shouldn't

The Allen-Bradley 1756-PA72 is the right choice for controls engineers and maintenance teams running standard-duty ControlLogix systems with AC mains, moderate module counts, and no requirement for redundancy or extended environmental ratings. Confirm all of the following before ordering:

  • Your system is ControlLogix 1756 — not CompactLogix or another PLC family
  • AC mains at 85…265 V, 47…63 Hz is available at the panel location
  • Total combined backplane load across all modules in that chassis does not exceed 75 W
  • No individual rail current exceeds 10 A at 5.1 V, 4 A at 3.3 V, or 2.8 A at 24 V
  • Standard industrial environment — no extreme contamination, high-vibration, or conformal-coating requirement
  • Redundant power supply architecture is not required for this chassis

If your application requires DC input, consider the 1756-PB72. For redundancy, look at the 1756-PA75R. For conformal coating in harsh environments, the 1756-PA72K is the correct variant. For higher combined power demands, the 1756-PA75 is the appropriate step up.

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What the 1756-PA72 Actually Does in a ControlLogix System

The Allen-Bradley 1756-PA72 is the standard AC power supply module for the ControlLogix 1756 chassis platform. Its function is straightforward but foundational: it takes whatever AC mains voltage is present between 85 and 265 V AC and converts it into the three regulated DC voltages the chassis backplane needs — 5.1 V, 3.3 V, and 24 V — to power every module installed in that rack. Without a properly sized supply occupying the left-most position, no controller, I/O module, or communication card in that chassis will operate.

The 75 W combined output limit is the number engineers must keep in mind throughout the lifecycle of the system. That figure is not just relevant at commissioning — every time a module is added, swapped, or upgraded, the power budget must be recalculated. Rockwell Automation documentation is explicit that the sum of backplane power across all rails cannot exceed the rated supply wattage, and individual rail current limits apply independently. A chassis running a 1756 CPU, a communications module, and a moderate count of I/O cards will typically fall well within budget; it is the incremental additions that catch teams off guard years into a machine's life.

The 1756-PA72 is an open-style module designed for mounting inside an enclosure. It has no integrated circuit breaker. Rockwell installation instructions specifically require that external branch circuit protection — a fuse or breaker sized per local electrical codes — be installed upstream of the supply terminals. This is not optional and is a compliance point for most machine safety standards.

Where the 1756-PA72 Sits in Your System Architecture

The 1756-PA72 sits immediately left of the CPU and module slots in the 1756 chassis, acting as the sole DC power source for everything installed in that chassis. It does not share power with adjacent chassis — each chassis in a multi-rack ControlLogix system requires its own dedicated supply.

  • Upstream: AC branch circuit, protected by an external fuse or breaker sized to local code requirements
  • At the supply: 1756-PA72 converts 85…265 V AC to 5.1 V DC, 3.3 V DC, and 24 V DC backplane rails within a 75 W combined limit
  • Backplane: 1756 ControlLogix CPU (e.g., 1756-L series controllers) draws from the 5.1 V and 3.3 V rails
  • I/O and communication modules: Each installed 1756 module draws its specified backplane power; total must not exceed per-rail and combined wattage limits
  • Downstream field devices: Powered separately — the 1756-PA72 does not supply field-side 24 V to sensors or actuators wired to I/O modules

Typical Applications and Deployment Scenarios

OEM machine builders standardizing on ControlLogix hardware for mid-complexity automation — packaging lines, conveyor systems, assembly stations — routinely specify the 1756-PA72 as the primary chassis power supply. A single-rack ControlLogix system with a CPU, an EtherNet/IP communications module, and a mix of digital and analog I/O cards represents the classic fit for this supply's 75 W budget.

In plant-wide control architectures where multiple 1756 chassis are distributed across a production floor — each handling a distinct process cell or machine zone — every chassis carries its own 1756-PA72, converting local AC panel power independently. This distributed approach avoids routing DC backplane power between enclosures and keeps each chassis's power supply failure isolated from the rest of the system.

Maintenance teams in automotive, food and beverage, and material handling facilities frequently order the 1756-PA72 as a direct replacement unit. Because the part number has been consistent over many years, it is a familiar component in spare-parts programs. For preventive maintenance programs, having at least one spare unit on the shelf eliminates the exposure of waiting for a distributor shipment after an in-service failure.

Process industries — oil and gas, water and wastewater, power generation — use ControlLogix as a PAC platform and specify the 1756-PA72 where AC mains is reliable and redundancy at the power supply level is not mandated by the site's safety or availability requirements. Where it is mandated, the 1756-PA75R is the appropriate starting point, not the 1756-PA72.

Application Typical Deployment
OEM machine control panel Single ControlLogix chassis with CPU, comms, and I/O; one 1756-PA72 per chassis
MRO replacement in existing rack Direct swap for failed or end-of-life 1756-PA72 in an operating production system
Multi-chassis plant-wide system Separate 1756-PA72 in each distributed ControlLogix rack; AC panel power available at each enclosure
New chassis expansion Additional 1756 rack added to a growing system; supply sized against new module list
Production line standardization Uniform supply specification across multiple lines to simplify spares inventory and maintenance training

Electrical Specifications and Variant Comparison

Parameter Rating
Input voltage range 85…265 V AC (nominal 120/240 V AC)
Input frequency 47…63 Hz
Total output power (combined backplane) 75 W maximum across all rails
Output — 5.1 V DC rail 10 A
Output — 3.3 V DC rail 4 A
Output — 24 V DC rail 2.8 A
Operating temperature 0…60 °C (per ControlLogix power supply datasheet)
Mounting position Left side of 1756 ControlLogix chassis
Enclosure style Open-style module; requires installation in an enclosure
External protection required Yes — external branch circuit protection mandatory

Full technical specifications are available on the product page at LeadTime.ca.

Model Input Type Output Power Redundancy Coating Best For
1756-PA72 AC 85…265 V 75 W No Standard Standard AC-powered ControlLogix chassis
1756-PA72K AC 85…265 V 75 W No Conformal coated Harsh or high-contamination environments
1756-PA75 AC input Higher than 75 W No Standard Chassis with higher module counts or power demands
1756-PA75R AC input Higher than 75 W Yes Standard Critical processes requiring redundant power supply architecture
1756-PB72 DC input Comparable to 75 W class No Standard Panels where only DC supply is available

If your chassis power budget exceeds 75 W combined, or if individual rail demands push above the per-rail limits, the 1756-PA75 is the appropriate next step — check current availability and compare options at LeadTime.ca.

Expert Verdict: Is the 1756-PA72 the Right Supply for Your Rack?

The Allen-Bradley 1756-PA72 earns its place as the default power supply specification for standard ControlLogix installations because it solves the most common case cleanly: AC mains available, moderate module count, no redundancy mandate, and a standard industrial enclosure. Controls engineers and maintenance teams running ControlLogix systems in general manufacturing, automotive, packaging, and food and beverage environments will find that a single 1756-PA72 covers a CPU, a communications module, and a representative mix of digital and analog I/O cards without pushing against the 75 W ceiling — provided the power budget has been calculated correctly. Its wide 85…265 V AC input range also makes panel design straightforward for sites with variable mains or for OEMs building machines for global deployment.

The 1756-PA72 has genuine limits that should push you toward a different model in specific situations. If your panel only has DC bus power — common in mobile equipment, marine, or certain process skids — the 1756-PB72 is the correct choice; the 1756-PA72 will not function on a DC source. If the chassis load across all modules approaches or exceeds 75 W, or if individual rail demands are close to the 10 A at 5.1 V, 4 A at 3.3 V, or 2.8 A at 24 V limits, move to the 1756-PA75 before commissioning rather than after. For mission-critical processes where an unplanned power supply failure would trigger significant downtime or safety consequences, the 1756-PA75R provides redundant capability that a single 1756-PA72 cannot match. And for environments with elevated contamination, moisture, or chemical exposure, the conformal-coated 1756-PA72K is the appropriate specification — the standard variant's open-style module construction is intended for clean industrial enclosures only.

From a procurement standpoint, the 1756-PA72 benefits from being one of the most recognized catalog numbers in the ControlLogix product line. Major North American distributors typically stock it, and same-day or next-day shipment is often achievable when units are on the shelf. Global buyers should factor in customs and transport when sourcing cross-border. The case for ordering through a specialist automation distributor rather than a generic supply channel is straightforward: a knowledgeable distributor can validate your chassis compatibility, confirm the power budget analysis, flag whether a different variant suits your environment, and give you an accurate read on lead time before you commit to a project schedule. Check current pricing and stock for the Allen-Bradley 1756-PA72 at LeadTime.ca — we ship worldwide.

For volume pricing, project BOM support, or to confirm lead time before finalizing your panel build, contact the LeadTime.ca team directly — we work with controls engineers and procurement specialists around the world.

What Engineers Need to Know Before Ordering the 1756-PA72

Model-specific community discussion around the 1756-PA72 is limited — forum activity on PLCTalk, PLCS.net, MrPLC, Reddit's automation communities, and Rockwell user forums tends to address ControlLogix power supplies as a category rather than this catalog number specifically. What that community record does consistently surface is a clear picture of how ControlLogix power supply problems arise in practice: almost universally, the root cause is either a sizing error, an incorrect variant specification, or a failure to keep a spare unit on hand. When community-level feedback is sparse for a specific part number, it is usually because the part is doing exactly what it is supposed to do when correctly specified — and the conversations that do exist focus on what happens when the specification step is skipped or rushed.

The most repeated theme across community discussions is the impact of a ControlLogix power supply failure on production. Engineers describe the downtime consequences as disproportionately large relative to the cost of the supply itself, which explains why maintaining at least one spare 1756-PA72 is considered standard practice on critical lines. A second theme is the underestimated power budget: teams that add modules to a chassis over time without recalculating the combined backplane load report intermittent controller resets and module faults that take time to trace back to a supply overload condition rather than a software or network issue. The 75 W combined limit on the 1756-PA72 is firm, and the per-rail limits at 5.1 V, 3.3 V, and 24 V are independent constraints — exceeding either will cause problems even if the total wattage appears acceptable on paper.

Ordering mistakes flagged in community discussions cluster around three patterns: confusing 1756-PAxx AC-input variants with 1756-PBxx DC-input variants when only one mains type is available at the panel; ordering the standard 1756-PA72 for an environment that actually requires a conformal-coated variant such as the 1756-PA72K; and selecting a 75 W supply for a chassis that is planned for expansion, leaving no power headroom once additional modules are installed. These are exactly the errors that a thorough pre-order review catches — and the reason specialist distributor support matters when community feedback is not available to catch the mistake for you.

Wiring and Installation Overview

The following points summarize installation requirements for the Allen-Bradley 1756-PA72. For complete wiring diagrams, conductor sizing tables, and torque specifications, consult the official Rockwell Automation installation instructions for the 1756-PA72.

  • De-energize the AC source and apply lockout/tagout before handling the module or making any wiring connections; confirm zero voltage at terminals before proceeding
  • Mount the 1756 chassis horizontally on a grounded back panel per Rockwell guidelines, then install the 1756-PA72 in the left-most position of the chassis
  • Connect AC line, neutral, and protective earth conductors to the appropriate supply terminals using conductor sizes and torque values specified in the Rockwell installation document; grounding continuity must be verified
  • Install external branch circuit protection — a correctly rated fuse or breaker — upstream of the supply terminals as required by both Rockwell installation instructions and applicable local electrical codes; the 1756-PA72 has no integrated protective device
  • After re-energizing, verify the power supply status indicator shows normal operation, confirm that all installed modules power up, and check controller diagnostics for any backplane voltage or load faults before placing the system into service

Wrong-Part Prevention Checklist

Before finalizing your order for the Allen-Bradley 1756-PA72, work through each item on this checklist verbatim — every point represents a documented source of mis-orders or commissioning failures:

  1. Confirm the system is ControlLogix 1756 and not CompactLogix or another PLC family.
  2. Verify chassis catalog number and size; check that one 75 W supply can support the total module load.
  3. Confirm AC mains is available at 85…265 V, 47–63 Hz; do not use this module where only DC supply is available.
  4. Check if redundancy is required; if yes, consider redundant-capable supplies instead.
  5. Confirm environmental conditions (temperature, enclosure, contamination) match standard (non-XT, non-conformal) ratings.
  6. Verify you are not mixing AC and DC supplies on the same chassis and that you have provisioned external branch protection.

If any item on this checklist raises a concern about your application, contact the LeadTime.ca team before ordering — our automation specialists can confirm the correct variant and check live stock.

Frequently Asked Questions

Can the 1756-PA72 power more than one ControlLogix chassis?

No. The 1756-PA72 provides backplane power only to the 1756 chassis in which it is installed. Each chassis in a multi-rack ControlLogix system requires its own dedicated power supply. Attempting to share one supply across multiple chassis is not a supported configuration per Rockwell Automation documentation.

How do I confirm that 75 W is enough for all the modules in my rack?

List every module planned for the chassis — CPU, communication cards, and all I/O modules — and obtain the backplane power draw for each rail from the respective module datasheet. Sum the draw on each rail and compare against the 1756-PA72's limits: 10 A at 5.1 V, 4 A at 3.3 V, 2.8 A at 24 V, and 75 W combined. If any figure is exceeded, or if the total sits close to the limit at the maximum expected ambient temperature, select a higher-power variant such as the 1756-PA75.

What is the practical difference between the 1756-PA72 and the 1756-PA75, and when should I step up?

The 1756-PA75 offers a higher combined output power rating than the 1756-PA72's 75 W limit, making it the appropriate choice when a larger module count or power-intensive I/O configuration pushes beyond what the 1756-PA72 can deliver. If your calculated backplane power budget approaches or exceeds 75 W, or if you are planning future expansion that will add modules, the 1756-PA75 provides the necessary headroom without requiring a supply swap later.

Is the 1756-PA72 compatible with a DC-only panel, or do I need the 1756-PB72?

The 1756-PA72 requires AC mains at 85…265 V, 47…63 Hz. It is not compatible with DC input sources. If your panel supplies only DC bus power — common in mobile, marine, or certain process applications — the correct variant is the 1756-PB72. Ordering the wrong input type is one of the most frequently cited ordering mistakes in the ControlLogix community.

What does the status indicator on the 1756-PA72 tell me, and what should I check first if the chassis loses power?

If the chassis loses power unexpectedly, first verify that AC input voltage is present and within the 85…265 V range, then check that the external branch circuit protection device has not opened. Confirm all wiring connections and grounding continuity are intact. If the supply itself has no visible status indication and AC input is confirmed good, review the module power budget — a sustained overload condition can cause supply shutdown even when input power is present.

What is the difference between the 1756-PA72 and the 1756-PA72K conformal-coated variant?

The 1756-PA72K carries conformal coating on its circuit board, providing additional protection against moisture, dust, and chemical contamination in harsh industrial environments. The electrical ratings and form factor are otherwise equivalent. If your application involves elevated humidity, condensation risk, or chemical vapors in the enclosure, the 1756-PA72K is the appropriate specification; the standard 1756-PA72 is intended for clean standard industrial enclosures only.

Why Order the Allen-Bradley 1756-PA72 From LeadTime.ca

  • Global shipping — LeadTime.ca sources and ships the 1756-PA72 and related ControlLogix hardware to buyers worldwide, including cross-border fulfillment for Canadian and international projects
  • Specialist knowledge — our team understands ControlLogix hardware selection, power budget validation, and variant differences so you avoid mis-orders before they happen
  • Accurate lead time information — we provide real stock and lead time data before you commit to a project schedule, reducing the risk of supply delays on critical builds
  • Volume and project pricing — contact us for BOM-level support, volume pricing, and MRO stocking program options
  • Hard-to-find and replacement stock — we regularly source ControlLogix components for maintenance teams that need parts quickly to minimize production downtime

At-a-Glance: Allen-Bradley 1756-PA72 Key Facts

  • AC input range: 85…265 V AC at 47…63 Hz — covers nominal 120 V and 240 V installations
  • Combined backplane output: 75 W maximum across all three DC rails simultaneously
  • Individual rail outputs: 5.1 V DC at 10 A, 3.3 V DC at 4 A, 24 V DC at 2.8 A
  • Mounting: Left side of any 1756 ControlLogix chassis; one supply per chassis only
  • Style: Open-style module requiring enclosure installation with external branch circuit protection
  • Operating temperature: 0…60 °C per ControlLogix power supply datasheet
  • Key alternatives: 1756-PA72K (conformal coated), 1756-PA75 (higher power), 1756-PA75R (redundant), 1756-PB72 (DC input)
  • Primary ordering risk: Confusing AC input (1756-PAxx) with DC input (1756-PBxx) variants, or selecting 75 W for a chassis planned for expansion
  • Spare inventory: Maintaining at least one spare 1756-PA72 is standard practice on critical production lines given the downtime impact of an unplanned supply failure

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