Allen-Bradley 1791-TB2 Flex I/O Terminal Base Unit Overview

Introduction

As industrial automation evolved from rigid relay panels to modular distributed I/O, the need for flexible, reliable field wiring grew. The Allen-Bradley 1791-TB2 terminal base unit emerged as a key component in this shift, offering a robust interface between sensors, actuators, and control systems. Part of the Flex I/O 1794 series, this terminal base unit simplifies installation and maintenance in demanding environments.

What Is the 1791-TB2?

The Allen-Bradley 1791-TB2 is a FLEX I/O terminal base unit designed for the 1794 series. It provides a cage clamp termination system for secure wire connections. This unit supports 2-wire screw termination and includes three terminal rows: one with 16 terminals, one with 18 terminals, and one with 2 terminals. It measures 3.7 x 2.7 x 3.7 inches and features an open-type enclosure. You can mount it on a panel or DIN rail.

Technical Specifications

The 1791-TB2 supports a wire size range of 0.21 to 1.3 mm² (24 to 16 AWG stranded copper wire with 3/64-inch insulation, category 2). It has a maximum current capacity of 10 Amps and a maximum voltage rating of 125 Volts AC/DC. The isolation voltage is 125V continuous, while channel-to-channel isolation depends on the inserted module. Operating temperature spans 0 to 55 degrees Celsius, with storage from -40 to 85 degrees Celsius. It withstands 5 g vibration at 10 to 500 Hertz, 30 g operating shock, and 50 g non-operating shock. The terminal screw torque range is 0.56 to 0.79 Nm (5 to 7 pounds on an inch).

Industry Applications

In manufacturing lines, the 1791-TB2 connects discrete sensors and actuators to a Flex I/O backplane. Its cage clamp design ensures vibration-resistant connections in conveyor systems and packaging machines. For process control, the unit handles up to 125V DC/AC signals, making it suitable for valve position feedback and motor starter monitoring. The compact 3.7-inch depth fits into tight control cabinets.

Installation & Setup Guidance

Mount the 1791-TB2 on a panel using the provided holes or snap it onto a DIN rail. Use stranded copper wire between 24 and 16 AWG with 3/64-inch insulation. Tighten terminal screws to 0.56-0.79 Nm (5-7 lb-in). Insert the I/O module by aligning the locking latch and pressing until it clicks. Connect the male and female Flexbus connectors to adjacent units for daisy-chain communication. The key switch prevents incorrect module insertion.

Maintenance & Reliability

Periodically inspect terminal connections for tightness, especially after temperature cycles or vibration. The open-type enclosure requires protection from dust and moisture in the cabinet environment. Operating within 0 to 55°C ensures long-term reliability. The unit has no user-serviceable internal parts; replace the entire base if damaged.

Compatible Systems

The 1791-TB2 works with all Allen-Bradley Flex I/O 1794 series modules, including analog, digital, and specialty I/O. It integrates with ControlLogix, CompactLogix, and SLC 500 controllers via the Flexbus backplane. Use 24 to 16 AWG category 2 wiring for signal connections.

Buying Guide

Before purchasing, verify that your I/O module matches the 1791-TB2's terminal configuration. This unit supports 2-wire devices. For complete technical specifications, please contact BluePLC Industrial. We stock genuine Allen-Bradley 1791-TB2 units with fast shipping.