Allen-Bradley 1746 SLC 500 Modules

Technical Dossier

Product Details And Specifications

Allen-Bradley 1746 SLC 500 Series: Comprehensive Module Range and Technical Overview

The Allen-Bradley SLC 500 (1746 series) is a modular programmable logic controller platform developed by Rockwell Automation. It has been deployed across heavy industrial sectors globally — including petrochemical refineries, nuclear auxiliary systems, offshore platforms, pulp and paper mills, and automotive assembly lines. The 1746 chassis-based architecture supports a wide range of discrete I/O, analog I/O, specialty function, and communication modules, making it one of the most extensively installed mid-range PLC platforms in industrial history. Installed base estimates place SLC 500 deployments in the hundreds of thousands of units worldwide, with many facilities maintaining active production lines dependent on this platform through extended lifecycle support agreements.

The Evolution of 1746 SLC 500 Architecture

The SLC 500 platform was introduced by Allen-Bradley in the late 1980s as a successor to the SLC 100 and SLC 150 fixed-format controllers. The 1746 series defined the modular expansion chassis format, allowing users to configure systems from 4-slot to 13-slot backplanes (1746-A4 through 1746-A13). Early CPU modules such as the 1747-L20 and 1747-L30 used DH-485 as the primary network protocol. Subsequent generations introduced DH+ (Data Highway Plus) and RS-232 DF1 communication, followed by EtherNet/IP-capable processors in the SLC 5/05 (1747-L553) generation.

The platform reached end-of-life (EOL) announcement from Rockwell Automation in 2012, with final production dates extending through 2022 for select modules. As of 2026, the SLC 500 is fully discontinued and classified as an obsolete product line. Rockwell's official migration path directs users toward the CompactLogix (1769 series) and ControlLogix (1756 series) platforms. However, due to the scale of installed base and the cost of full system migration, a significant portion of industrial facilities continue to operate SLC 500 systems under lifecycle extension strategies, relying on the secondary market for spare parts and repair services.

Compatibility considerations: 1746 I/O modules are chassis-slot compatible across all SLC 500 backplane generations. However, CPU firmware versions affect instruction set availability. Mixing 1746 modules across different chassis generations requires verification of backplane power budgets (1746-P2 vs. 1746-P4 vs. 1746-P7 ratings).

1746 SLC 500 Full Catalog & Functionalities (SKU List)

The following SKUs represent verified, commonly sourced modules within the Allen-Bradley 1746 SLC 500 product family. Modules are grouped by functional category.

CPU / Controller Modules

• 1747-L20B: SLC 5/01 CPU, 1K memory, DH-485 port, fixed 20-point I/O chassis
• 1747-L30B: SLC 5/01 CPU, 4K memory, DH-485, supports up to 3 expansion chassis
• 1747-L40B: SLC 5/02 CPU, 4K memory, enhanced instruction set, DH-485
• 1747-L541: SLC 5/04 CPU, 64K memory, DH+ and DH-485 ports
• 1747-L553: SLC 5/05 CPU, 64K memory, EtherNet/IP port, DH-485

Discrete Input (DI) Modules

• 1746-IA16: 16-point 120VAC discrete input module, screw terminal
• 1746-IB16: 16-point 24VDC sinking discrete input module
• 1746-IB32: 32-point 24VDC sinking discrete input, high-density format
• 1746-IV32: 32-point 24VDC sourcing discrete input, high-density format
• 1746-IM16: 16-point 220VAC discrete input module

Discrete Output (DO) Modules

• 1746-OW4: 4-point relay output module, Form C contacts, 240VAC/24VDC rated — the reference SKU for this listing
• 1746-OW16: 16-point relay output module, Form A contacts, 240VAC/24VDC
• 1746-OA16: 16-point 120/220VAC triac output module
• 1746-OB16: 16-point 24VDC sourcing transistor output module
• 1746-OB32: 32-point 24VDC sourcing transistor output, high-density
• 1746-OBP16: 16-point 24VDC protected transistor output with diagnostics

Analog Input (AI) Modules

• 1746-NI4: 4-channel analog input, configurable voltage/current, 12-bit resolution
• 1746-NI8: 8-channel analog input, configurable per channel, 12-bit
• 1746-NI16I: 16-channel current-only analog input, 16-bit resolution
• 1746-NT8: 8-channel thermocouple/mV input module, supports J/K/T/E/R/S/B types
• 1746-NR8: 8-channel RTD/resistance input module, supports Pt100/Pt1000/Ni

Analog Output (AO) Modules

• 1746-NO4I: 4-channel current analog output, 4–20mA, 12-bit resolution
• 1746-NO4V: 4-channel voltage analog output, 0–10V / ±10V, 12-bit
• 1746-NIO4I: 4-channel combination analog I/O, 2 inputs + 2 outputs, current

Communication & Specialty Modules

• 1746-BAS: BASIC language module for custom ladder-integrated programming
• 1746-HSCE: High-speed counter/encoder module, up to 1MHz input frequency
• 1746-QS: Stepper/servo positioning module, single-axis pulse output

Power Supply & Chassis

• 1746-P2: 120/240VAC power supply, 5VDC @ 5A / 24VDC @ 0.96A output
• 1746-P4: 120/240VAC power supply, 5VDC @ 10A / 24VDC @ 2.88A output
• 1746-P7: 24VDC input power supply, 5VDC @ 10A output, for DC-powered panels
• 1746-A4: 4-slot SLC 500 modular chassis
• 1746-A7: 7-slot SLC 500 modular chassis
• 1746-A13: 13-slot SLC 500 modular chassis, maximum expansion

Sourcing Hard-to-Find & Obsolete 1746 SLC 500 Parts

DriveKNMS maintains a dedicated inventory program for Allen-Bradley 1746 SLC 500 components. As the entire SLC 500 platform has been discontinued by Rockwell Automation, procurement through the secondary market is the primary channel for facilities that cannot justify full migration to CompactLogix or ControlLogix architectures.

DriveKNMS sources 1746 modules through decommissioned plant equipment, authorized surplus channels, and direct manufacturer overstock. All units are catalogued by part number, revision level, and firmware version where applicable. For CPU modules (1747-Lxxx series), firmware version documentation is retained to ensure compatibility with existing ladder logic programs. For I/O modules, slot compatibility and backplane power draw specifications are verified prior to dispatch.

Customers operating under long-term maintenance contracts for SLC 500 systems are encouraged to submit a full BOM (Bill of Materials) for standing inventory reservation. DriveKNMS can hold allocated stock against scheduled maintenance windows, reducing unplanned downtime risk for critical production assets.

Quality Control for the 1746 SLC 500 Range

Each 1746 module processed by DriveKNMS undergoes a structured inspection and functional test protocol before being classified as available inventory.

Physical inspection covers connector pin condition, backplane edge connector integrity, capacitor condition (visual inspection for bulge/leakage on electrolytic capacitors), and relay contact resistance measurement for output modules including the 1746-OW4 and 1746-OW16. Relay modules are cycled a minimum of 50 times under rated load to verify contact reliability.

Functional testing for discrete I/O modules is performed using a dedicated SLC 500 test chassis with a known-good 1747-L553 CPU. Each input channel is stimulated at rated voltage and verified for correct bit-level response in the processor image table. Each output channel is activated and verified for correct switching under resistive load.

Analog modules (1746-NI, 1746-NO, 1746-NT, 1746-NR series) are tested using calibrated signal sources and measurement instruments. Input accuracy is verified against published specifications (±0.1% full scale for 16-bit modules). Output linearity is verified across the full engineering range. Thermocouple and RTD modules are tested with precision decade resistance boxes and thermocouple simulators.

Communication modules and specialty function modules (1746-BAS, 1746-HSCE, 1746-QS) are tested under live PLC program execution to verify correct data exchange and function block operation.

All tested units are assigned a condition grade (Tested/Functional, Refurbished, or As-Removed) and documented with test date and technician ID prior to shipment.