Allen-Bradley 1771-A4B PLC Universal I/O Chassis | 16-Slot Rack Assembly

Overview

The 1771-A4B (Catalog Number: 1771-A4B) serves as a high-capacity foundation for Allen-Bradley PLC-5 systems. This 16-slot universal I/O chassis provides the mechanical framework and electrical backplane necessary for housing a diverse array of 1771-series modules. Engineered for back-panel mounting within a control enclosure, it ensures rigid support and high-current power distribution across the entire backplane bus, supporting both local and remote I/O configurations.

Technical Specifications

The 1771-A4B is designed to handle heavy-duty industrial loads and provide maximum module density.

• Slot Capacity: 16 Total I/O Slots

• Maximum Backplane Current: 24.0 Amperes @ 5V DC

• Mounting Configuration: Back-panel (Sub-panel) mounting

• Enclosure Architecture: Open-style chassis

• Operational Vibration: 2 g @ 10 to 500 Hz

• Shock Resistance: 15 g (Operational); 30 g (Non-operational)

• Physical Weight: 7.7 kg (14.8 lbs)

• Chassis Dimensions: Approximately 19.0 x 6.5 x 2.0 inches (Note: Standard 16-slot width is approximately 483 mm; verify enclosure clearance accordingly)

• Atmospheric Tolerance: 5% to 95% Relative Humidity (Non-condensing)

Environmental Operating Limits

This chassis is rated for continuous operation in standard industrial environments.

• Ambient Operating Temperature: 0°C to 60°C (32°F to 140°F)

• Storage/Transport Temperature: -40°C to 85°C (-40°F to 185°F)

Power Integration and Sourcing

The 1771-A4B backplane can be energized through multiple sourcing methods depending on the system architecture:

• Processor Sourced: Directly through the 1771 processor module.

• Chassis-Resident Modules: Slot-mounted power supply modules (e.g., 1771-P4, P7).

• Remote/External Sources: Heavy-duty standalone power supplies connected via the chassis power terminal strip.

Legacy System Comparison and FAQ

How does the 1771-A4B differ from the 1771-A1B?While both belong to the Universal I/O family, the 1771-A4B offers the maximum capacity of 16 slots, whereas the 1771-A1B is limited to 4 slots. The A4B is the preferred choice for centralized high-density I/O requirements.

Can this chassis be used with EtherNet/IP?The chassis itself is a passive backplane. However, by installing a 1771-AENTR adapter, this legacy 16-slot rack can be integrated into modern EtherNet/IP networks, allowing older I/O modules to communicate with ControlLogix or CompactLogix controllers.

What is the correct mounting orientation?For optimal thermal dissipation, the chassis should be mounted horizontally on a vertical back-panel. Ensure adequate spacing above and below the rack to allow for natural convection cooling of the installed modules.