Allen-Bradley 1791-8BR Block I/O Module Overview

Product Introduction

In industrial automation, reducing wiring costs and simplifying system architecture are constant challenges. The Allen-Bradley 1791-8BR Block I/O module addresses these needs by combining eight 24VDC input channels and eight normally open relay output channels in a single, compact unit. This rackless module mounts directly on a DIN rail or panel, integrating power supply, communication interface, and signal conditioning. It supports Remote I/O (RIO) protocol to connect with PLC-2, PLC-3, PLC-5/20, and PLC-5 controllers, making it a versatile choice for distributed I/O applications.

Technical Specifications

The 1791-8BR operates from an external power supply of 19.2-30V DC. Its input channels accept an on-state voltage range of 10-30V DC, with a typical rating of 24VDC. The relay output channels deliver a voltage range of 20-30V DC at 1A resistive maximum. Key input characteristics include an off-state voltage of 5V DC maximum, an on-state current of 11mA at 30V maximum, and an off-state current of 1.5mA minimum. The module weighs 1.00 lbs (0.45 kg) and supports both vertical and horizontal mounting orientations.

Industry Applications

The 1791-8BR excels in applications requiring local I/O processing near field devices. For example, in a packaging line, it can read signals from proximity switches and limit switches while controlling solenoid valves or motor starters. Its compact design eliminates long cable runs, reducing installation costs and improving signal integrity. In material handling systems, the module interfaces with PLC-5 controllers via RIO to manage conveyor zones. The relay outputs handle resistive loads up to 1A, making them suitable for pilot devices and small actuators.

Installation & Setup Guidance

Mount the 1791-8BR on a standard DIN rail or directly on a panel using the provided slots. Use 14-gauge stranded wire with 3/64 maximum insulation thickness for signal connections. Connect incoming power to terminals +24 (1), RET +24 (3), and GND (2). For Remote I/O communication, wire terminals BLU (6), CLR (8), and SHD (7). The module does not include internal fusing; install external fuses to protect both the module and external circuits from overcurrent. Avoid parallel output connections as they lower overall circuit resistance.

Maintenance & Reliability

Regularly inspect the 1791-8BR for signs of dust accumulation or loose connections. Verify that the external power supply remains within the 19.2-30V DC range. Check relay output contacts for wear if switching inductive loads frequently. The module's internal protection safeguards the internal circuitry, but external fuses are essential for comprehensive system protection. Periodically test the RIO communication link to ensure reliable data exchange with the controller.

Compatible Systems & Integration

The 1791-8BR integrates with Allen-Bradley PLC families including PLC-2, PLC-3, PLC-5/20, and PLC-5. It works with scanner modules such as the 1771-SN, 1772-SD, 1772-SD2, 1775-S5, 1775-SR5, and the PLC-5VME (6008-LTV) module. The module supports Remote I/O (RIO) protocol, enabling connection to RIO scanners and controllers. Compatible input devices include proximity switches, limit switches, selector switches, float switches, pushbutton switches, and auxiliary contacts. Output devices include solenoid-actuated devices, motor starters, and resistive loads.

Selection Guide & Purchasing Advice

Before purchasing the 1791-8BR, verify that your controller supports Remote I/O (RIO) protocol and that the external power supply meets the 19.2-30V DC requirement. Confirm the number of inputs and outputs needed—this module provides 8 inputs and 8 outputs per block. For complete technical specifications, please contact BluePLC Industrial. We stock genuine Allen-Bradley products and can assist with compatibility and availability inquiries.