The Allen-Bradley 1771-A4B serves as the primary 1771-A4B Universal Input/Output Chassis utilized to execute physical module mounting and backplane power distribution across PLC-5 platforms.
Hardware Specifications
Parameter
Specification
Model
1771-A4B
Brand
Allen-Bradley
Origin
USA
Weight
13.36 lbs (6.06 kg)
Dimensions
16-Slot 1771 Chassis Footprint
Operating Temp
0 to 60 deg C
Power Consumption / Capacity
Max 24.0 A at 5.25 VDC backplane current
Product Line
PLC-5
Product Type
I/O Chassis / Rack
Number of Slots
16 Slots
Rated Voltage
5.25 VDC (Backplane)
Mounting Style
Panel Mount / 19-inch Rack Mount
Deterministic Backplane & Power Scaling
The hardware structure ensures backplane bus communication velocity and signal integrity across all 16 slot positions. Designed to handle backplane bus current loads up to 24 A at 5.25 VDC, the chassis provides low-impedance power routing and physical card guidance for a full array of I/O, processor, and communication modules. The mechanical alignment slots enforce rigid connector mating, eliminating transmission attenuation and preserving backplane bus scanning speed across high-density I/O configurations.
Frequently Asked Questions
Q: What is the maximum backplane current rating for the 1771-A4B chassis?
A: The chassis backplane bus is rated to deliver up to 24 A at 5.25 VDC. Total combined current draw of all installed processor, adapter, and I/O modules must not exceed this limit.
Q: Can any module be placed in Slot 0 of the 1771-A4B?
A: No. Slot 0 (the leftmost slot) is reserved specifically for local PLC-5 processors, Remote I/O adapters (such as the 1771-ASB), or ControlNet interface modules that drive the backplane bus.
Field Installation Guidelines
Mount the chassis securely to a grounded panel or enclosure backplate using standard mounting hardware to prevent mechanical vibration and stress on card connections.
Connect a heavy-gauge copper bonding jumper (minimum 10 AWG) from the dedicated enclosure ground lug directly to the central chassis grounding terminal.
Ensure adequate clearance (minimum 2 inches / 50.8 mm) around the top, bottom, and sides of the rack to maintain proper thermal heat dissipation profile.
Verify power supply voltage outputs (5.25 VDC nominal) before connecting external power supplies to the backplane wiring arm or power connectors.
Fully seat all 1771 I/O cards into their respective slot guide rails and engage top/bottom latching arms before applying system power.
