Allen-Bradley 1756-A17/B ControlLogix Chassis

Configured for modular I/O and controller backplane interconnection in ControlLogix systems, the Allen-Bradley 1756-A17/B (1756-A17/B PLC chassis rack) provides direct electrical distribution and high-speed module-to-module communication across a 17-slot backplane architecture. The chassis supports horizontal-only installation and distributes 5.1 VDC, 3.3 VDC, 1.2 VDC, and 24 VDC power rails to installed ControlLogix modules via the integrated backplane bus.

Hardware Specifications

ControlLogix Backplane Power Distribution and Bus Structure

The 1756-A17/B chassis implements a shared backplane architecture where all installed modules draw regulated DC rails from the chassis power supply interface. Backplane bus communication is handled through deterministic ControlLogix high-speed signaling, supporting synchronized I/O data exchange and controller task scheduling across multiple slots.

The 17-slot density requires controlled I/O segmentation to maintain backplane current compliance, particularly on the 5.1 VDC rail where total chassis load is limited to 15 A. Slot-level current constraints enforce module distribution planning for mixed analog, digital, and communication modules.

Frequently Asked Questions (FAQ)

Q: Can modules be hot-swapped while the chassis is energized?
A: Hot-swap capability depends on installed module type. The chassis backplane remains powered; module-level removal requires adherence to ControlLogix safe removal sequencing to avoid backplane data disruption.

Q: Does each slot independently limit current consumption?
A: Yes. Slot-level limits apply for 3.3 VDC, 5.1 VDC, and 24 VDC rails, independent of total chassis current limits, preventing localized overcurrent conditions.

Q: Does the chassis support redundant power supply configurations?
A: Redundancy behavior is defined by the installed ControlLogix power supply modules; the chassis itself provides passive distribution without redundancy logic.

Field Installation Guidelines

Install the chassis on a rigid back-panel using all designated mounting points. Maintain horizontal alignment to ensure uniform backplane connector engagement across all 17 slots. Ground the chassis using 8 AWG functional earth conductor and 14 AWG protective earth conductor as specified.

Route backplane and field wiring separately to avoid coupling noise into module signal paths. Ensure cabinet ventilation supports IEC thermal limits. Do not leave unused slots open without approved slot fillers to maintain airflow and mechanical stability.