Allen‑Bradley 1746‑A4 SLC 500 4‑Slot Modular PLC Chassis

1746‑A4 is a 4‑slot modular backplane chassis under Rockwell Allen‑Bradley SLC 500 PLC series, officially discontinued in March 2024. It acts as the mechanical and electrical carrier for SLC power supply, CPU processor, digital/analog I/O and communication modules, delivering integrated power distribution and backplane data bus transmission for small compact control systems. It adopts natural convection cooling without extra fans, and all plug‑in modules can be freely arranged in any slot position for flexible layout.

This chassis supports multi‑rack expansion via 1746‑C7/C9 interconnection cables; up to three chassis can be cascaded to expand total slots to 30. With industrial metal perforated housing and panel mounting brackets, it fits small‑scale automation cabinets. As obsolete legacy hardware, it is mainly supplied as maintenance spare parts for old production lines that still run SLC 500 control systems worldwide.

Main Specifications

• Brand: Allen‑Bradley (Rockwell Automation); Model: 1746‑A4; Series: SLC 500 Modular Chassis
• Slot Quantity: 4 module slots; Power supply must be installed on the leftmost slot
• Backplane Power Rating: 5.1 VDC 10 A, 24 VDC 2.88 A total current capacity
• Physical Dimensions: 171 mm (H) × 177 mm (W) × 145 mm (D); Weight approx 0.8 kg
• Cooling Method: Passive natural convection, no forced fan required
• Operating Temperature: 0 ℃ ~ +60 ℃; Storage: -40 ℃ ~ +85 ℃
• Mounting Standard: Direct panel backplate mounting with four metal fixing lugs
• Expansion Compatibility: Cascadable with 1746‑C7/C9 interconnection ribbon cables
• Lifecycle Status: Discontinued since March 31, 2024, no official replacement model
• Compatible Modules: All SLC 1746 series I/O, 1747‑Lxx CPU processors, 1746‑P power supplies

Core Functions

• Provide unified mechanical mounting structure for SLC power supply, CPU, analog/digital I/O and fieldbus communication modules inside control cabinets.
• Built‑in printed backplane bus distributes DC power and transmits high‑speed parallel data signals between all inserted modules without external wiring.
• Support flexible slot arrangement: CPU, input/output and communication modules can be placed in any available slot except the power supply position.
• Enable multi‑chassis system expansion through dedicated interconnection cables to increase total I/O points for expanded production process control.
• Perforated metal shell accelerates heat dissipation of power and I/O modules, ensuring stable long‑term operation under normal industrial cabinet temperature.
• Standardized grounding structure reduces electromagnetic interference from inverters and high‑voltage equipment to protect backplane communication signals.

Application Scenarios

• Small standalone PLC control cabinet rack replacement for packaging machinery, material conveyors and small assembly lines.
• Maintenance spare chassis for vintage SLC 500 automation systems in water treatment, textile and food processing factories.
• Compact local I/O expansion rack for auxiliary equipment of metallurgical cooling pumps and boiler auxiliary control systems.
• Retrofit backup stock for old printing, plastic injection and packaging equipment equipped with Allen‑Bradley SLC control platforms.
• Small‑scale distributed I/O sub‑rack for remote signal collection in chemical plant workshop auxiliary control cabinets.
• Global aftermarket spare inventory for automation maintenance workshops servicing discontinued Rockwell SLC 500 control hardware.