When Coax Reaches Its Limit, What Keeps ControlNet Running?
Long cable runs, ground loops, and electrical noise are the classic enemies of a stable ControlNet trunk. The Allen-Bradley 1786-RPFRL answers that challenge. This fiber ring long-distance repeater converts electrical ControlNet signals into optical signals, extending reach far beyond coaxial limits while adding noise immunity and ground-loop isolation.
Part of the ControlNet / Bulletin 1786 family from Allen-Bradley (Rockwell Automation), the 1786-RPFRL is a discontinued module. Oil AutoTech keeps practical supply channels open for hard-to-find ControlNet spares, so you can keep existing lines running while planning a migration.
What the 1786-RPFRL Does on Your Network
The module operates on a deterministic, scheduled ControlNet network at 5 Mbps. It uses multimode fiber at 820 nm with ST connectors, supporting up to 3 km per segment. In a ring topology, the network can reach up to 20 km with a 15 dB loss limit. Two BNC coax ports and two ST fiber ports let the repeater bridge copper trunk segments into a fiber ring.
A 24V DC supply draws 570 mA at 5V DC (3.02W), and 50V isolation protects the network from ground-loop problems. Status LEDs and a fault relay contact simplify diagnostics during commissioning and maintenance. The IP20 housing suits clean control-cabinet environments, with an operating range of 0 to 60 C.
Technical Specifications
| Specification | Value |
|---|---|
| Product Type | Fiber Ring Repeater (Long Distance) |
| Network | ControlNet, 5 Mbps |
| Fiber Type | Multimode fiber, 820 nm, ST connectors |
| Segment Distance | Up to 3 km per segment |
| Ring Distance | Up to 20 km, 15 dB loss limit |
| Ports | 2x BNC coax + 2x ST fiber |
| Supply | 24V DC, 570 mA at 5V DC (3.02W) |
| Isolation | 50V |
| Operating Temperature | 0 to 60 C |
| Enclosure Rating | IP20 |
Where It Fits: Long Runs, Harsh Electrical Environments
Picture a large process plant where the ControlNet trunk must cross a switchyard, a pump house, and a remote tank farm. Copper alone cannot make that trip without noise and grounding headaches. The 1786-RPFRL turns those segments into a fiber ring, keeping communications deterministic across the full distance.
In oil and gas terminals, the same logic applies. Long conveyor lines, remote valve manifolds, and outdoor I/O cabinets benefit from fiber isolation. The repeater also supports redundant media concepts common in ControlNet architectures, which helps protect uptime in continuous processes.
Integration and Replacement Notes
ControlNet fiber ring designs often require careful planning of cable types, connectors, and ring paths. If you are integrating this repeater into an existing network, confirm your fiber and coax cabling with a knowledgeable supplier before ordering. Oil AutoTech offers hands-on technical selection help for ControlNet spares and can point you toward practical options.
Because the 1786-RPFRL is discontinued as of 2022-09-30, Rockwell points to an engineering replacement path such as the 1786-RPFRXL or other ControlNet fiber ring alternatives. For plants still running the original design, sourcing the exact module is often the fastest way to restore a line. Contact Oil AutoTech today for pricing and availability.
Maintenance and Reliability
Fiber ring repeaters have no moving parts, so reliability depends mainly on the environment and connections. Inspect ST and BNC connectors periodically for contamination or looseness. Keep the cabinet within the 0 to 60 C operating range and respect the IP20 rating by avoiding dust and moisture ingress. Watch the status LEDs and fault relay contact for early signs of ring degradation. Please verify current lifecycle status and availability with Oil AutoTech before ordering.
FAQ
Is the 1786-RPFRL still available?
It is discontinued as of 2022-09-30. Oil AutoTech can help you check current availability and discuss replacement options.
What fiber and connectors does it use?
It uses multimode fiber at 820 nm with ST connectors, plus two BNC coax ports for the electrical trunk.
How far can one segment reach?
Up to 3 km per segment, with a ring reach of up to 20 km and a 15 dB loss limit.
What power does it require?
A 24V DC supply drawing 570 mA at 5V DC (3.02W), with 50V isolation.
Can it replace a standard coax repeater?
It is designed for long-distance fiber ring applications, converting electrical ControlNet signals to optical signals. Confirm your topology with a technical specialist before substituting.
