Why the 1746-OW8/A Still Matters in Legacy SLC 500 Panels
Rockwell Automation discontinued the 1746-OW8/A on 2022-12-31, yet thousands of SLC 500 control panels still run daily in packaging, material handling, and process lines. This eight-channel electromechanical relay output module switches both AC and DC field loads through isolated normally-open contacts. If your panel carries this module, you already know the challenge: replacement stock is finite, and migration takes planning. This buyer’s guide helps you decide whether to source remaining units or plan an engineering replacement.
What the 1746-OW8/A Delivers
The 1746-OW8/A is an open-style relay output module in the SLC 500 / Bulletin 1746 family. Its eight normally-open outputs split into two groups of four, each with its own common. That grouping lets one module control mixed-voltage devices. The operating voltage range spans 5-265 VAC or 5-125 VDC, so the same module drives 24 VDC pilot devices and 120 VAC motor starters.
Current capacity matters in relay-based panels. Each output handles 1.5 A at 120 VAC or 1.2 A at 24 VDC. Each common carries 8 A continuous, and the full module carries 16 A continuous. These limits let you group loads intelligently instead of spreading them across extra modules.
Key Specifications at a Glance
| Parameter | Value |
|---|---|
| Outputs | 8 normally-open relay, 2 groups of 4 |
| Operating voltage | 5-265 VAC or 5-125 VDC |
| Current per output | 1.5 A at 120 VAC; 1.2 A at 24 VDC |
| Current per common | 8 A continuous |
| Current per module | 16 A continuous |
| Backplane current | 85 mA at 5V DC; 90 mA at 24V DC |
| Signal delay | 10 ms ON / 10 ms OFF |
| Isolation | 1500 VAC contacts to backplane |
| Operating temperature | 0 to 60 C |
Reading the Specs Like a Buyer
Relay isolation of 1500 VAC between contacts and backplane protects the controller from field transients. The 10 ms ON / 10 ms OFF delay suits motor starters, solenoids, and alarms, though it limits high-speed pulse duties. Backplane draw stays modest at 85 mA at 5V DC and 90 mA at 24V DC, which eases power budgeting in a full chassis.
Where This Module Fits
Factory automation panels use the 1746-OW8/A to drive interposing relays and pilot devices. Packaging equipment relies on its mixed AC/DC switching for diverters and seal bars. Material handling systems use the two commons to separate conveyor zones. Process control panels use it for alarms and valve pilots where isolated contacts prevent ground loops.
Replacement and Upgrade Path
Because the platform is discontinued, buyers face two routes. First, source remaining 1746-OW8/A units to keep existing panels running without re-engineering. Second, migrate to Compact 5000 I/O with the Logix platform, which Rockwell recommends. Migration changes wiring, chassis, and programming, so many plants stage it during planned outages while keeping spare 1746 modules on the shelf.
Installation and Setup Notes
The module mounts in a 1746 I/O chassis, and Slot 0 stays reserved for the processor or a 1747-ASB adapter. The module is not hot-swappable: never install, remove, or wire it with power applied. Field-side load power requires an external supply, since the backplane only provides logic power. Removable terminal blocks simplify field wiring, and Bulletin 1492 pre-wired interface options exist for faster changeouts.
Maintenance and Reliability
Electromechanical relays wear with switching cycles, so track high-cycle outputs and inspect terminals periodically. Keep panel temperature within 0 to 60 C and humidity within 5-95% non-condensing. Follow the manufacturer’s safety manual for all service work. For buyers, a disciplined spare-parts stock reduces downtime risk as remaining supply tightens.
Buyer’s Checklist Before You Order
Confirm your chassis model, slot assignment, and load voltages. Verify per-output and per-common current against your field devices. Check whether your panel needs the Bulletin 1492 interface. Since the 1746-OW8/A is discontinued, verify current lifecycle status and availability with SpareTechPLC before ordering, and ask about engineering replacement options for long-term planning.
Frequently Asked Questions
Is the 1746-OW8/A still in production?
No. Rockwell Automation discontinued it on 2022-12-31. SpareTechPLC can confirm remaining availability.
Can I mix AC and DC loads on one module?
Yes. The two groups of four outputs and the 5-265 VAC / 5-125 VDC range support mixed-voltage control.
What is the maximum current per common?
Each common carries 8 A continuous, and the module carries 16 A continuous.
Can I hot-swap this module?
No. Do not install, remove, or wire it with power applied.
What replaces the 1746-OW8/A?
Rockwell recommends migration to Compact 5000 I/O with the Logix platform as an engineering replacement.
