Product Overview

The Allen-Bradley 1786-FS20 is a preassembled fiber optic cable used in Allen-Bradley ControlNet communication networks. It provides a 20-meter optical connection between compatible fiber interfaces, particularly the 1786-RPFS short-distance fiber repeater.

Unlike conventional coaxial ControlNet cables, the 1786-FS20 transmits communication signals through optical fiber. This makes it useful when network connections need to cross electrically noisy areas, connect separate control cabinets, or link automation equipment installed in different sections of a production facility.

The cable uses 200-micron fiber and factory-installed V-pin connectors. These connectors match the Versalink V-System interface used by the short-distance fiber repeater arrangement. Because the assembly is preterminated, technicians do not need to perform connector installation at the job site.

A typical application involves connecting fiber repeater interfaces between two automation cabinets. For example, a PLC cabinet may communicate with a remote machine control panel through a fiber connection rather than extending the coaxial network directly through an electrically noisy production area.

The 20-meter cable length makes the 1786-FS20 suitable for installations where a 10-meter assembly is insufficient but a longer cable would introduce unnecessary routing slack. It belongs to the same ControlNet fiber cable family as the 1786-FS10, 1786-FS60, 1786-FS100, 1786-FS200, and 1786-FS300.

The 1786-FS20 is a passive transmission component. It carries optical signals between compatible interfaces but does not independently convert electrical signals, amplify communication signals, or manage network traffic. These functions are handled by the connected repeater hardware.

For maintenance engineers, connector cleanliness and cable handling are important considerations. Contamination at the fiber ends, excessive bending, or physical damage can increase optical loss and interrupt communication between network sections.

Technical Specifications

Product Features

• 20-Meter Cable Assembly: Provides a factory-terminated optical connection for ControlNet installations requiring a 20-meter cable route.
• 200/230 µm HCS Fiber: Uses hard-clad silica fiber matched to the ControlNet short-distance repeater system.
• V-Pin Connectors: Features factory-installed connectors compatible with the Versalink V-System interface.
• 1786-RPFS Compatibility: Intended for use with Allen-Bradley short-distance fiber repeater modules.
• Electromagnetic Interference Immunity: Optical transmission avoids direct electromagnetic interference coupling into the communication signal.
• Preterminated Construction: Reduces field installation work by eliminating the need for on-site connector termination.
• Passive Signal Transmission: Carries optical communication signals without requiring an independent power supply.
• PVC Cable Jacket: Provides external protection during normal industrial cable routing.
• Flexible Network Layout: Supports optical connections between separated ControlNet equipment locations.
• Industrial Installation Capability: Suitable for connecting automation equipment in electrically noisy environments.

Product Working Principle

The 1786-FS20 carries ControlNet communication signals through an optical fiber path between compatible repeater interfaces.

In a conventional ControlNet coaxial network, electrical signals travel through the trunk cable between network devices. When an optical connection is required, a compatible repeater converts the electrical communication signals into optical signals before transmission through the fiber cable.

The 1786-FS20 carries these optical signals through its HCS fiber core. At the receiving end, the connected optical interface converts the signals back into electrical form for the next ControlNet network section.

A simplified communication path is:

ControlNet Coaxial Network → 1786-RPA → 1786-RPFS → 1786-FS20 → Remote Fiber Interface → ControlNet Network

The cable itself does not perform signal conversion. Its function is to maintain the optical transmission path between the connected devices.

The 200/230 µm HCS fiber construction is matched to the short-distance repeater architecture. Its V-pin connectors establish the optical connection with the corresponding Versalink interfaces.

The optical power budget is another important consideration. The specified 4.2 dB allowance represents the permitted total optical loss across the fiber link, including fiber attenuation, connectors, and other connection losses.

Mechanical handling also affects transmission performance. Excessive bending, pulling, or crushing can damage the fiber and increase attenuation. Maintaining the specified bend radius and protecting the connector ends help preserve communication quality.

Role in Allen-Bradley ControlNet Network Architecture

The 1786-FS20 functions as the optical transmission link in an Allen-Bradley ControlNet fiber repeater arrangement. It connects compatible fiber modules and allows communication signals to pass between equipment areas without requiring a continuous electrical connection.

A mixed-media ControlNet installation may use coaxial trunk cables for the main network and fiber connections where electrical isolation or separation between equipment areas is required.

A typical arrangement is:

ControlNet Coaxial Trunk → Network Tap → 1786-RPA → 1786-RPFS → 1786-FS20 → Remote Fiber Interface → ControlNet Network

The 1786-FS20 is particularly useful where a ControlNet installation requires a preassembled optical connection between compatible short-distance fiber interfaces.

Industrial Applications

The 1786-FS20 is suitable for industrial facilities that use ControlNet fiber repeaters to connect separated automation equipment or reduce the effects of electrical interference on communication links.

Installation and Maintenance

1. Verify Cable Compatibility: Confirm that the 1786-FS20 is being used with compatible 200/230 µm HCS fiber interfaces and the appropriate ControlNet repeater hardware.
2. Check Repeater Interfaces: Verify that the connected equipment supports the V-pin connector arrangement used by the short-distance fiber system.
3. Inspect the Cable Assembly: Examine the cable jacket and connector ends for visible cuts, deformation, contamination, or other damage.
4. Clean the Connectors: Clean the optical connector surfaces using suitable fiber cleaning materials before making the connection.
5. Protect Unused Connectors: Keep protective caps installed whenever the cable is disconnected from network equipment.
6. Plan the Cable Route: Select a path that avoids sharp edges, moving machinery, crushing forces, and unnecessary mechanical stress.
7. Maintain the Bend Radius: Keep the cable bend radius at or above the specified minimum of 25 mm throughout installation.
8. Control Pulling Force: Do not exceed the maximum installation pull tension of 490 N when routing the cable through trays or conduits.
9. Connect the Fiber Interfaces: Align the V-pin connectors with the corresponding Versalink ports on the compatible repeater modules.
10. Provide Cable Support: Secure the cable along its route so that the connector assemblies do not carry the weight of unsupported cable sections.
11. Verify Network Communication: Restore the system and check the repeater status and communication between the connected ControlNet network sections.
12. Document and Store: Record the cable route and connection points. If the cable is removed, reinstall protective caps and store it where the fiber cannot be crushed or kinked.

During troubleshooting, inspect connector cleanliness and cable routing before replacing repeater modules. A contaminated optical interface or damaged fiber can interrupt communication even when the electronic modules are functioning normally.

Compatible System Components

Recommended Related Models

Key Advantages

• 20-meter preassembled cable for ControlNet fiber connections.
• 200/230 µm HCS fiber construction.
• Factory-terminated Versalink V-System connectors.
• Compatible with the Allen-Bradley 1786-RPFS repeater.
• Optical transmission avoids direct electromagnetic interference coupling.
• Reduces field connector termination work.
• Supports mixed coaxial and fiber ControlNet network layouts.

Technical FAQs

1. What is the difference between the 1786-FS20 and 1786-FS10?

Both models belong to the ControlNet short-distance fiber cable family and use 200-micron fiber with V-pin connectors. The main difference is cable length: the 1786-FS20 provides a 20-meter connection, while the 1786-FS10 provides a 10-meter connection.

2. Which ControlNet repeater is compatible with the 1786-FS20?

The 1786-FS20 is intended for use with the Allen-Bradley 1786-RPFS short-distance fiber repeater. The repeater provides the optical interface required to connect the fiber cable to the ControlNet network architecture.

3. Can the 1786-FS20 be installed near variable-frequency drives?

Yes. Optical fiber does not carry electrical communication signals through copper conductors, so the link is not directly affected by electromagnetic interference in the same way as conventional coaxial cabling. Appropriate cable routing and mechanical protection are still necessary.

4. What should be checked if the 1786-FS20 connection loses communication?

Inspect both V-pin connector ends for contamination or incomplete connections. Then check the cable for excessive bending, kinks, or physical damage. If the cable is intact, verify the 1786-RPFS module status and confirm that the total optical link loss remains within the specified 4.2 dB power budget.