Allen-Bradley 1791-8BC Block I/O Module: Compact 24VDC I/O Node

Technical Specifications

• Brand: Allen-Bradley
• Model: 1791-8BC
• Product Line: 1791 Block I/O
• Input Channels: 8 DC sinking.
• Input Voltage Range: 10 to 30 VDC.
• Output Channels: 8 DC sourcing.
• Output Voltage Range: 10 to 30 VDC.
• Output Current (Vert. Mount): 1A @ 30°C, 500mA @ 60°C.
• External Power: 19.2–30 VDC, 300 mA max.
• Power Dissipation: 11.8 Watts max.
• Communication: Allen-Bradley RIO Protocol.
• Status LEDs: Per channel & system OK.
• Wire Size: 14 AWG stranded max.

Performance & Network Details

• Output current capacity depends on mounting orientation and temperature.
• The RIO network runs at 57.6K, 115.2K, or 230.4K baud over Belden 9463 cable.
• Input circuits require a minimum of 2.5 mA at 10 VDC to guarantee an ON state.
• Network termination requires a 150-ohm (57.6K/115.2K) or 82-ohm (230.4K) resistor.
• Thermal dissipation is a relatively low 41 BTU/hour maximum.

Installation & Integration Guide

• Mount the 1791-8BC on a DIN rail vertically for the highest output current rating.
• Connect a clean 19.2-30 VDC power supply to the external power terminals.
• Wire field devices like proximity sensors to the eight 24VDC input points.
• Connect output loads such as small relays or pilot lights to the DC output terminals.
• Use the designated terminals (BLU, SHD, CLR) to daisy-chain the RIO communication cable.
• Always install the correct terminating resistor at the first and last node on the RIO link.

Packaging & Shipping

• The module arrives securely packaged in an individual box to ensure protection.
• Package Includes: One Allen-Bradley 1791-8BC Block I/O Module.
• International shipping is available via FedEx, UPS, and DHL.
• We provide a tracking number as soon as your order leaves our warehouse.

Frequently Asked Questions (FAQ)

• Q: Why does the output current rating change with mounting?
  A: Heat dissipation differs. Vertical mounting allows better air cooling, supporting a higher continuous current.
• Q: Can I use the 1791-8BC with a modern ControlLogix PLC?
  A: Yes, but you need a compatible Remote I/O scanner module in the ControlLogix chassis to communicate.
• Q: How do I know if the module is working?
  A: Check the per-channel LEDs for I/O status and the green OK LED for system health.
• Q: What type of wire should I use for connections?
  A: Use 14 AWG stranded copper wire maximum for reliable connections to the terminal blocks.

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