Technical Specifications
Product Model | 1746-A7Manufacturer | Rockwell Automation / Allen-BradleyProduct Type | SLC 500 7-Slot Chassis (Passive Backplane Rack)Series | Allen-Bradley SLC 500Total Slots | 7 (Slot 0 = Power Supply, Slot 1 = Processor/Scanner, Slots 2–6 = I/O Modules)Maximum Expandable Slots | Up to 30 total (with 2 additional expansion chassis via 1746-C7 / 1746-C9)Backplane Voltage | 5.1 V DC (logic) / 24 V DC (I/O sense, from power supply module)Backplane Current Capacity | 5 V DC @ 10 A max, 24 V DC @ 2.88 A max (dependent on installed 1746-PS module)Backplane Isolation | 500 V AC RMS (backplane to chassis ground)Expansion Port | 25-pin D-shell female (rear) for connection to 1746-C7 / 1746-C9 expansion cableMounting Method | 35 mm DIN rail (EN 60715) snap-mount or panel-mount via rear holesOperating Temperature | 0 °C to +60 °C (+32 °F to +140 °F)Storage Temperature | -40 °C to +85 °CHumidity (non-condensing) | 5 % to 95 % RHDimensions (H × W × D) | approx. 177 mm × 343 mm × 146 mm (7.0″ × 13.5″ × 5.75″)Weight | approx. 2.3 kg (5.1 lb)Agency Approvals | UL Listed, cULus, CE Marked, C-TickChassis Variants in Series | 1746-A4 (4-slot), 1746-A7 (7-slot – this model), 1746-A10 (10-slot)
Main Features and Advantages
The Allen-Bradley 1746-A7 delivers a time-tested, cost-effective chassis platform that has supported millions of installed SLC 500 control systems globally. Its seven-slot configuration strikes a popular balance—large enough to accommodate a typical mixed-I/O application (processor + several discrete and analog modules) yet compact enough for space-conscious enclosures. The clearly defined slot numbering (0 through 6) simplifies I/O addressing in RSLogix™ 500 / Studio 5000 programming software, reducing commissioning errors and easing troubleshooting for maintenance staff already familiar with the SLC 500 architecture.A key advantage of the Allen-Bradley 1746-A7 is its expandability. Through the rear 25-pin expansion connector, users can cascade one or two additional SLC 500 chassis—retaining a single processor while distributing I/O physically closer to field devices. This reduces wiring runs and allows zone-based panel layouts. The passive backplane in the Allen-Bradley 1746-A7 is insensitive to firmware changes and requires no configuration; as long as the installed 1746 power supply can support the cumulative backplane current draw, modules simply plug in and are auto-recognized by the CPU.Mechanical design also favors the installer: the Allen-Bradley 1746-A7 features guide rails that align modules squarely with the backplane edge connector, a positive cam-lock lever on each module to ensure full seating, and end-plate covers to prevent accidental contact. DIN rail mounting enables quick rack installation in pre-fabricated panels, and the painted metal enclosure provides RFI/EMI shielding consistent with industrial immunity standards. For legacy system sustainment programs, the Allen-Bradley 1746-A7 remains available as new-old-stock or fully tested refurbished stock, ensuring that long-life assets can be kept running without compromise.
Application Field
The Allen-Bradley 1746-A7 is predominantly found in small-to-medium machine control and process skid applications that were originally engineered around the SLC 500 platform. Typical use cases include stand-alone packaging machines, conveyor sorting systems, palletizers, bottling lines, and batch blending stations where a compact PLC with localized I/O meets the control requirement. In these scenarios the Allen-Bradley 1746-A7 houses a 1747-L532 (SLC 5/03) or 1747-L541 (SLC 5/04) processor alongside 1746-IB16 / 1746-OB16 digital I/O and 1746-NI4 / 1746-NO4I analog modules, all communicating with HMIs or SCADA via DH-485, DF1, or EtherNet/IP (via 1747-AENTR on newer retrofits).The Allen-Bradley 1746-A7 is also common in water/wastewater pump stations, HVAC control panels for large commercial buildings, and food & beverage auxiliary processes where the control logic is stable and does not warrant a full platform migration. Many OEMs continue to source the Allen-Bradley 1746-A7 for spare racks and duplicate machines to maintain consistency across a fleet of installed equipment. Even in plants that have migrated the main process to ControlLogix, satellite SLC 500 racks built on the Allen-Bradley 1746-A7 often persist as remote I/O drops bridged through a 1747-ASB scanner module or a 1756-DHRIO bridge. For any application requiring a proven, easily serviced, and widely understood small PLC chassis, the Allen-Bradley 1746-A7 continues to deliver dependable service.
Related Products
- 1746-A4 — 4-slot SLC 500 chassis (Slot 0 Power + Slot 1 CPU + 2 I/O slots); smaller footprint alternative to the 1746-A7.
- 1746-A10 — 10-slot SLC 500 chassis (Slot 0 Power + Slot 1 CPU + 8 I/O slots); larger capacity version of the 1746-A7.
- 1746-P1 — 120 V AC input power supply module for SLC 500 chassis; installs in Slot 0 of the 1746-A7.
- 1746-P2 — 220–240 V AC input power supply module for SLC 500 chassis; commonly paired with the 1746-A7.
- 1746-P4 — 24 V DC input power supply module for SLC 500 chassis; used in DC-powered enclosures with the 1746-A7.
- 1747-L532 — SLC 5/03 (OS401) CPU module (DH-485 + RS-232); typical processor installed in Slot 1 of a 1746-A7.
- 1747-L541 — SLC 5/04 CPU module (DH+ & RS-232); higher-performance processor option for the 1746-A7.
- 1746-C7 — 1-meter (3 ft) expansion cable connecting a 1746-A7 local chassis to an expansion chassis.
- 1746-C9 — 2-meter (6 ft) expansion cable for SLC 500 chassis-to-chassis expansion from the 1746-A7.
- 1746-NI4 / 1746-IB16 / 1746-OB16 — Example analog and digital I/O modules that plug into I/O slots of the 1746-A7.
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