Allen-Bradley 1791-OA32 High-Density AC Module

Allen‑Bradley 1791‑OA32 High‑Density AC Output Module

Overview and Key Features

The 1791‑OA32 belongs to the Allen‑Bradley 1791 Block I/O family. You get thirty‑two discrete AC output channels in four groups of eight. Each group shares a common return. This module operates with a nominal 120 VAC and a wide range of 20-132 VAC.

Additionally, the 1791‑OA32 includes a built‑in adapter for Remote I/O (RIO) protocol. It works as a distributed I/O station. You can connect it directly to RIO scanners from PLC‑2, PLC‑3, and PLC‑5 families. Specifically, compatible scanners include the 1771‑SN, 1772‑SD, 1772‑SD2, 1775‑S5, and 1775‑SR5.

Technical Specifications

• Outputs per block: 32

• Channel grouping: 4 groups of 8 channels

• Output voltage range: 20-132 VAC (nominal 120 VAC)

• Minimum on‑state current: 50 mA per output

• Maximum on‑state current: 300 mA per output

• Surge current: 10 A for 50 ms, repeatable every 2 seconds

• Off‑state leakage current: 3 mA

• Output delay OFF→ON: 1.0 ms at 60 Hz or 50 Hz

• Output delay ON→OFF: 8.3 ms at 60 Hz; 10.0 ms at 50 Hz

• External power required: 85-132 VAC

Furthermore, the 1791‑OA32 provides a peak voltage drop of only 1.5V at 300mA. This ensures efficient operation with most AC loads.

Environmental and Mechanical Ratings

• Operating temperature: 0 to 60 °C

• Mounting orientation: Vertical or horizontal

• Vertical mounting output rating:

  • 600 mA at 30 °C

  • 300 mA at 60 °C

• Horizontal mounting output rating:

  • 300 mA at 30 °C

  • 150 mA at 60 °C

Therefore, always consider the temperature and orientation for derating. This prevents overheating and extends module life.

Wiring and Connections

Power connections use terminals L1 (1), N (3), and GND (2). Meanwhile, Remote I/O (RIO) wiring connects to terminals BLU (6), CLR (8), and SHD (7). All these terminals are on the left side of the module.

To set the I/O rack number, open the front cover. The same cover gives access to the I/O group switch assembly. Status LEDs on the front cover help during troubleshooting.

Common Applications

The 1791‑OA32 easily drives many output devices. For instance, you can connect motor starters, solenoid actuators, indicators, and signaling devices. Additionally, it handles other resistive or inductive AC loads up to 300 mA continuous.

Maximum inrush current reaches 10 A (1200 W) for 50 ms. Holding current capacity is 300 mA (36 W) at 60 °C or 600 mA (72 W) at 30 °C. This makes the 1791‑OA32 suitable for small contactors and pilot lights.

Installation Guidelines

First, verify the operating voltage is between 85 and 132 VAC external supply. Next, mount the block vertically or horizontally using the integral mounting holes. Then connect the RIO cable to the blue, clear, and shield terminals. Finally, set the correct I/O rack number using the front panel switches.

Do not exceed the maximum on‑state current per channel. For horizontal mounting at 60 °C, limit each output to 150 mA. For vertical mounting at the same temperature, the limit is 300 mA.

Packaging List

• 1791‑OA32 module (1 unit)

• Terminal block (pre‑installed)

• Product label

• Quick start guide (printed)

Note: No certificates or warranty documents are included. These items are available upon request.

Shipping Information

We ship worldwide via FedEx, UPS, or DHL. The gross weight is 0.45 kg (1.00 lbs). All shipments include tracking and basic insurance.

Frequently Asked Questions (FAQ)

1. Is the 1791‑OA32 compatible with modern ControlLogix systems?
No, the 1791‑OA32 uses Remote I/O (RIO) protocol. It works with PLC‑2, PLC‑3, and PLC‑5 scanners, but not directly with ControlLogix without a RIO scanner module.

2. Can I mix AC and DC outputs on the same 1791‑OA32 block?
No, all 32 outputs on the 1791‑OA32 are AC only (20-132 VAC). For DC outputs, choose a different 1791 block I/O model.

3. What happens if I exceed the 300 mA per channel rating?
Exceeding 300 mA may cause overheating or internal damage. Additionally, the module may enter thermal shutdown. Always derate for high temperature or horizontal mounting as specified.

4. How do I replace a failed 1791‑OA32 in an existing system?
First, disconnect external power and the RIO cable. Then remove the front cover and note the rack number switch settings. Install the replacement 1791‑OA32 with identical switch positions. Finally, reconnect power and verify communications.

5. Does the module provide output short‑circuit protection?
The 1791‑OA32 has no internal short‑circuit protection per channel. Use external fuses (fast‑blow, rated for 132 VAC) to protect each group or individual outputs.