Allen-Bradley 1771-A4B 16-Position I/O Chassis

Allen-Bradley 1771-A4B is a 16-slot universal I/O chassis from the 1771 I/O family, designed to host up to sixteen 1771 I/O modules on a single backplane for PLC-5/SLC 500 style automation systems. This chassis is typically paired with the 1771-P2 power supply to provide the necessary field-powering for all installed I/O modules, and it uses the modular design and swing-arm style mounting common to 1771 backplanes. The -A4B designation identifies the largest configuration in the four-size line—the family includes -A1B (4 slots), -A2B (8 slots), -A3B (12 slots), and -A4B (16 slots)—allowing you to scale I/O capacity within a single rack. In practice, the 1771-A4B serves as a centralized, 16-position chassis for distributing digital and analog I/O across a control network, enabling straightforward expansion or retrofit of existing PLC-5/SLC 500 installations in manufacturing, packaging, and material handling environments. This chassis accepts a broad range of 1771 I/O modules, making it a flexible backbone for projects requiring reliable, modular field I/O in a compact 16-slot form factor.