Product Overview

The Allen-Bradley 1771-OA is a high-reliability AC digital output module designed for the legacy PLC-5® Universal I/O platform. This module serves as an interface between the controller and various AC-powered field devices, providing eight independent channels of 120V AC switching capability. Engineered for the rigors of heavy industrial environments, the 1771-OA facilitates the control of high-current loads such as motor starters, large solenoids, and heavy-duty indicators by translating the low-level logic signals from the backplane into high-voltage output states.

As a single-slot module, the 1771-OA maximizes chassis density while providing robust protection features. Each channel is designed with individual fusing to prevent internal circuitry damage from field wiring shorts, and the module includes comprehensive front-panel diagnostics to minimize downtime during fault finding.

Operational Characteristics and Protection

The 1771-OA is optimized for driving inductive and resistive loads with high surge tolerances.

• Switching Performance: Each of the eight channels can handle a continuous current of 1.5A at 120V AC. For high-inertia loads like large magnetic contactors, the module supports a significant surge current of up to 4A for a duration of 8.3 milliseconds.

• Intelligent Diagnostics: The faceplate features eight red status LEDs for real-time output verification. A critical secondary "FUSE" indicator illuminates specifically to alert maintenance personnel of a blown fuse condition, streamlining the troubleshooting process.

• Safety Isolation: Provides 1500V RMS galvanic isolation between the field wiring and the backplane logic, ensuring that high-voltage transients on the plant floor do not compromise the PLC processor.

• Thermal Management: Efficiently managed power dissipation (maximum 11.1 Watts) allows the module to operate reliably in ambient temperatures up to 60°C (140°F).

• Load Management: Total module output is rated at a maximum aggregate current of 6A, ensuring safe operation when multiple channels are energized simultaneously.

Technical Specifications

• Manufacturer: Allen-Bradley (Rockwell Automation)

• Model Number: 1771-OA

• Output Type: AC Digital (Triac)

• Number of Outputs: 8 Channels

• Operating Voltage: 92V–138V AC

• Frequency Range: 47–63 Hz

• Backplane Current: 210mA @ 5V DC

• Continuous Output Current: 1.5A per channel (6A max per module)

• Minimum Load Current: 50mA per channel

• Off-State Leakage: 5mA (maximum)

• Module Keying: Positions 4–6 or 12–14

• Physical Dimensions: 3.5 x 13.0 x 14.5 cm

• Weight: 0.9 kg (1.98 lbs)

Installation and Field Application

The 1771-OA is a standard component for large-scale automation systems in diverse sectors:

• Heavy Manufacturing: Controlling AC motor starters and high-wattage status beacons.

• Process Control: Operating large solenoid-actuated valves for fluid and gas management.

• Infrastructure: Managing audible alarms and warning sirens in plant-wide safety systems.

• Power Plants: Driving interposing relays for high-voltage switchgear control.

To ensure proper installation, the module requires a 1771-WN field wiring arm. This allows for the disconnection of the module without removing any field wires, significantly reducing the complexity of hardware swaps.