PRODUCT INFORMATION
Product Overview
The Allen-Bradley 1791-8BC Block I/O 1791 I/O Module provides combination discrete input and output functionality. It features eight 24 VDC discrete inputs and eight 24 VDC discrete outputs. The unit uses a rackless design that mounts on standard DIN rail. Communication occurs over Remote I/O networks using Belden 9463 or 1771-CD three-wire cable. Supported network transmission rates include 57.6K, 115.2K, and 230.4K baud.
External power requires a 19.2 to 30 VDC power supply with 300 mA maximum current draw. Both inputs and outputs operate across an operational voltage range of 10 to 30 VDC. Vertical mounting permits an output current of 500 mA at 60 degrees Celsius. Horizontal mounting provides 250 mA per point at 60 degrees Celsius. Internal thermal dissipation is rated at 11.8 watts and 41 BTU per hour.
TECHNICAL DATA
Technical Specifications
| Parameter | Specification |
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| Category | PLCs |
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| Current Draw | 300 mA, maximum |
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| External Power | 19.2-30V dc |
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| External Power supply | 19.2–30V dc |
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| Input Off-state Current | 1.5mA min. |
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| Input Off-state Voltage | 5V dc max. |
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| Input On-state Current | 11mA @ 30V max. |
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| Input On-state Voltage Range | 10-30V dc |
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| Input signal, nominal | 24 VDC |
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| Input signal, range | 10-30 VDC |
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| Inputs per Block | 8 |
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| LED indicators | Individual channel LED indicators; OK LED; |
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| No. of I/O channels | Sixteen (16) |
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| No. of Output channels | Eight (8) |
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| No. of input channels | Eight (8) |
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| Off-state current | 1.5mA |
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| On state current | 11.0mA @ 30V, max; 2.5mA @ 10V, min. |
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| Output Voltage Range | 10-30V dc |
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| Output current | Vertical mounting: 500mA @ 60oC, 1A @ 30oC Horizontal mounting: 250mA @ 60oC, 500mA @ 30oC |
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| Output voltage | 10-30 VDC |
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| Outputs per Block | 8 |
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| Product Description | Combination Discrete Input and Output Module |
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| Product Lifecycle Status* | Discontinued/Obsolete |
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| UPC | 612598127085 |
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| Voltage | 24V dc |
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| Weight | 2.00 lbs (0.91 kg) |
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TECHNICAL INFORMATION
Features
- Eight discrete 24 VDC inputs arranged in a single group.
- Eight discrete 24 VDC outputs operating between 10 and 30 VDC.
- Rackless hardware structure supporting direct DIN rail mounting.
- Remote I/O transmission rates of 57.6K, 115.2K, and 230.4K baud.
- Individual channel status indicators and an overall OK LED indicator.
- Low thermal dissipation rated at 11.8 watts and 41 BTU per hour.
TECHNICAL INFORMATION
Applications
- Distributed machine-level discrete sensor and actuator interfacing.
- Remote I/O drops for PLC-5 and SLC 500 controller networks.
- Logix platform field I/O expansion via Remote I/O communication modules.
TECHNICAL INFORMATION
Connections / Interfaces
- Remote I/O connects to terminals 6 (BLU), 7 (SHD), and 8 (CLR).
- The network uses Belden 9463 or 1771-CD three-wire communication cable.
- Terminating resistors connect across terminals 6 and 8 on endpoint nodes.
- Use 150-ohm terminating resistors for 57.6K and 115.2K baud rates.
- Use 82-ohm terminating resistors for 230.4K baud communication.
- Terminal connections accept up to 14 AWG stranded wire with 3/64 inch insulation.
TECHNICAL INFORMATION
Installation Guidelines
- Mount the module on standard DIN rail in a distributed enclosure.
- Vertical mounting supports up to 500 mA output current at 60 degrees Celsius.
- Horizontal mounting derates maximum output current to 250 mA at 60 degrees Celsius.
- Connect an external 19.2 to 30 VDC power supply to the unit.
TECHNICAL INFORMATION
Compatibility
- Allen-Bradley PLC-2 and PLC-3 control platforms.
- Allen-Bradley 1785 PLC-5 controller systems.
- Allen-Bradley 1747 SLC 500 systems via Remote I/O scanners.
- CompactLogix and ControlLogix systems using Remote I/O communication modules.
TECHNICAL INFORMATION
Lifecycle / Replacement Information
- Rockwell Automation lists the 1791-8BC module status as discontinued and obsolete.
COMPATIBILITY
Compatibility & Replacement
COMPATIBLE MODELSAllen-Bradley PLC-2 and PLC-3 control platforms. Allen-Bradley 1785 PLC-5 controller systems. Allen-Bradley 1747 SLC 500 systems via Remote I/O scanners. CompactLogix and ControlLogix systems using Remote I/O communication modules.
Verify compatibility against the exact Part Number, revision and manufacturer documentation before ordering.
PART VERIFICATION
Before You Order
Industrial automation parts can share similar model names, suffixes and revisions. Confirm the complete manufacturer Part Number before purchase.
01Check Part NumberMatch the complete ordering code on the existing unit.
02Confirm RevisionCheck suffix, hardware or firmware when applicable.
03Send a Label PhotoWe can review a clear label photo when identification is uncertain.
ORDERING PROCESS
From RFQ to Dispatch
1Submit Part Number2Verify Product Identity3Confirm Stock & Condition4Issue Quotation5Dispatch & Tracking
PRODUCT FAQ
Frequently Asked Questions
What communication protocol does the 1791-8BC module use?
The module uses Remote I/O communication at 57.6K, 115.2K, or 230.4K baud over three-wire cable.
What input and output configurations are available on the 1791-8BC?
The module provides eight 24 VDC inputs and eight 24 VDC outputs operating from 10 to 30 VDC.
How does mounting orientation affect the output current rating?
Vertical mounting allows 500 mA at 60 degrees Celsius. Horizontal mounting lowers the rating to 250 mA.
What termination resistors are needed on the Remote I/O network?
Install 150-ohm resistors for 57.6K or 115.2K baud. Install 82-ohm resistors across terminals 6 and 8 for 230.4K baud.
