Allen-Bradley 1756-A4/B ControlLogix Chassis

Configured for module hosting and backplane signal distribution in ControlLogix architectures, the Allen-Bradley 1756-A4/B (1756-A4/B PLC chassis) provides direct electrical and communication interconnection for 1756-series power supplies and I/O modules within a 4-slot backplane structure. The chassis operates as a passive backplane carrier with fixed horizontal installation constraints and distributed power routing across installed modules.

Suffix Breakdown & Model Matrix

No formal functional segmentation is defined in the provided data for 1756-A4/B. The “/B” designation is treated as a hardware revision indicator within the 1756-A4 chassis family.

Hardware Specifications

ControlLogix Backplane Communication Characteristics

The 1756-A4/B chassis implements a passive ControlLogix backplane structure supporting deterministic module-to-module communication via system bus arbitration. I/O density scaling is constrained by the 4-slot architecture, with timing synchronization and data exchange governed by installed controller and communication modules over the shared backplane infrastructure. Firmware and module compatibility are determined at system level by ControlLogix platform revision alignment.

Frequently Asked Questions (FAQ)

Q: Can the 1756-A4/B chassis support hot-swap of I/O modules?
A: Hot-swap capability is dependent on installed module type and ControlLogix controller configuration. The chassis itself provides passive backplane connectivity without switching logic.

Q: What limits backplane current distribution in the 1756-A4/B?
A: Current limits are defined per voltage rail (1.2 V, 3.3 V, 5.1 V, 24 V DC) and are enforced by the installed power supply and module loading across the shared backplane.

Q: Does chassis revision “/B” affect firmware compatibility?
A: Firmware execution is not hosted by the chassis. Compatibility is determined by ControlLogix controller firmware and installed module revision levels.

Field Installation Guidelines

Install the chassis on a rigid back-panel using horizontal orientation only. Ensure all mounting points are mechanically secured to prevent vibration-induced backplane stress. Maintain correct grounding using functional earth and protective earth conductors as specified by system design. Route backplane power and communication modules according to ControlLogix layout rules, avoiding cable strain on installed modules. Ensure enclosure integration due to open-style chassis design, and maintain clearance for thermal dissipation and service access.