Allen-Bradley 1756-OA8E ControlLogix 8-Point AC Output Module

Technical Overview

The Allen-Bradley 1756-OA8E serves as a high-performance discrete output interface within the ControlLogix PLC platform. This module specifically manages the switching of AC loads by providing eight independent output channels, which are organized into two isolated groups of four. It operates within a nominal voltage range of 120V AC, though the hardware effectively handles fluctuations between 74V AC and 132V AC. Because the unit features electronic fusing for every individual point, it offers superior protection against overcurrent conditions compared to standard non-electronically fused modules.

Operational Performance and Signal Management

The 1756-OA8E excels in high-speed switching environments. It achieves transition times as low as 9.3 ms at 60 Hz, ensuring that the control system responds rapidly to logic changes. To maintain system stability, the module draws power from the backplane at two levels: 200 mA at 5.1V DC and 250 mA at 24V DC. Furthermore, the electronic fusing mechanism acts as a critical safety barrier, as it protects both the module and the connected field devices from potential damage.

The thermal design of the module allows it to dissipate 18.76 BTU/hr, which helps maintain a stable internal temperature during heavy duty cycles. When engineers install this unit, they typically utilize the 1756-TBNH or 1756-TBSH Removable Terminal Blocks (RTB) to facilitate secure and organized field wiring. Even though Rockwell Automation officially categorized this module as discontinued in late 2012, it remains a vital component for maintaining existing legacy ControlLogix architectures.

Key Technical Specifications

• Brand: Allen-Bradley / Rockwell Automation
• Model Number: 1756-OA8E
• Module Type: Electronically Fused AC Output
• Product Family: ControlLogix
• Number of Outputs: 8 Channels (2 groups of 4)
• Voltage Range: 74V AC to 132V AC (50/60 Hz)
• Current Rating per Point: 2 A at 60°C
• Total Module Current: 4 A at 60°C / 8 A at 30°C
• Surge Current Capability: 20 A for 43 ms
• Power Dissipation: 5.5 Watts
• Dimensions: 14.5 x 13.2 x 3.5 cm
• Country of Origin: USA

Industrial Applications

• Driving AC solenoids and small motor starters in automated assembly lines.
• Managing signaling lights and alarm sirens in industrial facilities.
• Interfacing with high-voltage discrete actuators in water treatment plants.
• Providing reliable AC switching for legacy PLC systems in manufacturing.