Allen-Bradley 1746-P4/A Retrofit Power Supply for SLC 500

Allen-Bradley 1746-P4/A Retrofit Power Supply for SLC 500 Legacy Systems

The Allen-Bradley 1746-P4/A is a high-capacity AC power supply module designed for the SLC 500 modular chassis platform. With an output rating of 10A at 5VDC and 1.5A at 24VDC, this unit is the preferred retrofit-compatible replacement for aging SLC 500 control panels that require a direct drop-in power upgrade without chassis modification. As Rockwell Automation has transitioned its primary PLC portfolio toward the ControlLogix and CompactLogix families, the 1746-P4/A remains a critical spare part for facilities committed to extending the operational life of their existing SLC 500 infrastructure.

At NINERMAS, every 1746-P4/A unit is sourced from verified supply channels, subjected to pre-shipment functional testing under load conditions, and shipped with a 12-month warranty. Our inventory program is designed to support long-term spare parts commitments, ensuring that your maintenance team can access this module on short notice without compromising production continuity.

Upgrade Compatibility Table

Retrofit Planning for Existing Automation Systems

When planning a retrofit around the 1746-P4/A, the first step is a full power budget audit of the target chassis. Engineers should calculate the aggregate 5VDC and 24VDC draw across all installed modules — including the SLC 5/04 or SLC 5/05 processor, any 1746-NI4 analog input modules, 1746-NO4I analog output modules, 1746-IB32 high-density digital input modules, and 1746-OB32 digital output modules. The 1746-P4/A’s 10A at 5VDC headroom makes it the appropriate choice when the existing 1746-P2 (5A) or 1746-P3 (8A) supply is operating near its thermal limit or triggering nuisance faults under peak load.

Terminal wiring during the swap requires careful attention. The AC input terminals on the 1746-P4/A are physically identical to those on the 1746-P2 and 1746-P3, so existing field wiring can typically be transferred without re-termination. However, maintenance teams should verify wire gauge compliance with the 1746-P4/A’s terminal torque specification (typically 0.8 N·m) and confirm that the upstream circuit breaker rating is appropriate for the higher inrush current capacity of the P4 variant.

For systems that include a 1747-L542 or 1747-L553 processor with an active 1747-KE DH-485 to RS-232 communication module, the retrofit window should be coordinated with the control room to avoid interrupting live HMI sessions on PanelView 550 or PanelView 900 terminals. The HMI communication link will drop during the power cycle, and operators should be briefed to expect a 2–3 minute reconnection delay while the SLC processor re-establishes its DH-485 token ring.

If the retrofit is part of a broader I/O expansion — for example, adding a 1746-HSCE high-speed counter module or a 1746-BAS BASIC module for custom ladder logic extensions — the 1746-P4/A’s additional current capacity provides the necessary headroom without requiring a chassis upgrade. This is particularly valuable in brownfield installations where the control cabinet has limited physical space and replacing the chassis would require significant re-engineering of the panel layout.

For sites running DeviceNet networks managed by a 1747-SDN scanner module, the retrofit should include a verification of the DeviceNet node address table stored in the SLC processor’s data file. After the power supply swap and processor restart, the SDN scanner will re-poll all nodes on the network; any nodes that fail to respond within the configured electronic keying timeout will generate a fault. Pre-retrofit documentation of all node addresses and EDS file assignments is strongly recommended to accelerate post-restart commissioning.

Downtime Control During System Migration

Minimizing unplanned downtime is the primary concern for any SLC 500 power supply replacement. The 1746-P4/A swap is a cold-swap procedure — the chassis must be de-energized before the module is removed. To protect the existing program logic, the SLC processor’s user program should be uploaded to RSLogix 500 and saved to a local engineering workstation before the maintenance window begins. This backup ensures that if the processor’s battery-backed RAM has degraded, the program can be reloaded immediately after power restoration without requiring a full re-commission from the original source code.

A structured replacement sequence significantly reduces exposure time. The recommended approach is to: (1) notify all HMI operators and place the process in a safe hold state, (2) de-energize the chassis and lock out the upstream disconnect, (3) photograph the existing terminal wiring for reference, (4) remove the failed or degraded 1746-P2 or 1746-P3 unit, (5) install the 1746-P4/A and re-terminate the AC input wiring, (6) restore power and verify the green PWR LED illuminates without fault, and (7) confirm the SLC processor returns to RUN mode and all I/O modules report healthy status in the RSLogix 500 I/O tree.

For critical production lines where even a 30-minute outage carries significant cost, NINERMAS recommends maintaining a pre-tested 1746-P4/A unit on-site as a hot spare. Our inventory commitment program allows customers to reserve stock at a fixed price for up to 12 months, ensuring that the spare is available when needed without exposure to spot-market price volatility for discontinued Rockwell Automation components.

Sites that have already migrated their primary control platform to a 1769-L33ER CompactLogix or 1756-L73 ControlLogix processor but retain legacy SLC 500 sub-panels for auxiliary functions — such as conveyor interlocks, utility monitoring, or legacy recipe management — will find the 1746-P4/A essential for maintaining those sub-panels in reliable operation until a full platform migration can be scheduled and budgeted.

Retrofit Support FAQ

Q1: Is the 1746-P4/A a direct replacement for the 1746-P2 and 1746-P3?
Yes. The 1746-P4/A is physically and electrically compatible with all SLC 500 modular chassis (1746-A4 through 1746-A13) and installs in slot 0 without modification. It provides higher output current than the P2 and P3 variants, making it a safe upward-compatible replacement. No software changes are required in the SLC processor program.

Q2: What commissioning steps are required after installation?
The 1746-P4/A requires no software configuration. After installation, restore AC power and verify the PWR LED status. Power-cycle the SLC processor and confirm it returns to RUN mode. Check the I/O status tree in RSLogix 500 to ensure all modules are communicating normally. If a 1747-SDN DeviceNet scanner is present, allow 60–90 seconds for the network to re-establish before clearing any scanner faults.

Q3: Does NINERMAS provide pre-shipment testing documentation?
Yes. Every 1746-P4/A unit shipped by NINERMAS is tested under load prior to dispatch. A test record confirming output voltage stability at 5VDC and 24VDC under rated current is available upon request. All units are covered by a 12-month warranty from the date of shipment.

Q4: Can NINERMAS support long-term supply commitments for this part?
Yes. NINERMAS operates a spare parts lifecycle program specifically for discontinued and long-lead Rockwell Automation components. Customers can reserve inventory at a fixed price for up to 12 months, with scheduled release dates aligned to planned maintenance windows. Contact our team at sale@ninermas.com or +0086 187 5021 5667 to discuss a supply agreement.