1746-OA8 vs 1746-OA16: Output Count and Current Limits
A direct comparison of 1746-OA8 and 1746-OA16 output count, common grouping, backplane current and temperature-derated load limits.
The Allen-Bradley 1746-OA8 and 1746-OA16 are SLC 500 AC output modules. Both switch 85–265 V AC loads, but their point count and current limits differ.
Technical comparison
| Specification | 1746-OA8 | 1746-OA16 |
|---|---|---|
| Outputs | 8 | 16 |
| Points per common | 4 | 8 |
| Operating voltage | 85–265 V AC, 47–63 Hz | 85–265 V AC, 47–63 Hz |
| Backplane current at 5 V DC | 0.185 A | 0.370 A |
| Maximum continuous current per point at 30 °C | 1.0 A | 0.50 A |
| Maximum continuous current per point at 60 °C | 0.50 A | 0.25 A |
| Maximum continuous current per module at 30 °C | 8.0 A | 8.0 A |
| Maximum continuous current per module at 60 °C | 4.0 A | 4.0 A |
| Maximum signal delay, resistive load | 1 ms on; 11 ms off | 1 ms on; 11 ms off |
| Maximum off-state leakage | 2 mA | 2 mA |
| Minimum load current | 10 mA | 10 mA |
Check point current before increasing density
The 1746-OA8 permits twice the per-point current of the 1746-OA16 at the same ambient temperature.
The module-level limit is the same for both catalog numbers. A 16-point replacement therefore needs a load-by-load current check, not only a total-current calculation.
Backplane and wiring checks
- Allow 0.370 A at 5 V DC for the 1746-OA16, compared with 0.185 A for the 1746-OA8.
- Confirm the common grouping: four points per common on the OA8 and eight on the OA16.
- Check each load against the temperature-derated point limit.
- Verify minimum load current and off-state leakage for small relays or indicators.
- Retain the original terminal schedule before moving conductors.
Primary source
Rockwell Automation publication 1746-IN027D-EN-P, “SLC 500 Digital I/O Modules Installation Instructions,” December 2012, pages 36–37.