Redundancy System Fiber Optic Cable Solution – Allen-Bradley 1756-RMC3 | ControlLogix RM Series
In mission-critical industrial facilities — power generation plants, oil & gas terminals, water treatment stations, and automotive assembly lines — an unplanned PLC controller failure can cost between $10,000 and $500,000 per hour in lost production, regulatory penalties, and emergency maintenance. Yet many facilities still operate single-controller ControlLogix architectures where a single CPU fault triggers a full process shutdown. The root cause is not the controller itself, but the absence of a properly synchronized, low-latency redundancy link between the primary and secondary chassis.
The Allen-Bradley 1756-RMC3 is the 3-meter RM (Redundancy Module) fiber optic cable engineered specifically to interconnect two ControlLogix 1756-RM2 redundancy modules. By transmitting chassis synchronization data over a dedicated fiber link — immune to EMI, ground loops, and electrical noise — the 1756-RMC3 enables sub-10ms switchover from primary to secondary controller without process interruption. This single cable is the physical backbone of a ControlLogix Hot-Standby redundancy system, transforming a vulnerable single-point-of-failure architecture into a continuously available control platform.
Where This Product Is Used
Power Generation & Utilities
- Turbine governor control systems — synchronizing primary/secondary ControlLogix chassis in gas and steam turbine applications where trip events must be avoided; ambient temperatures up to 55°C, high-vibration environments; IEC 61511 SIL 2 compliance required.
- Substation automation and SCADA integration — redundant PLC chassis linked via 1756-RMC3 in 480V/11kV switchgear control rooms; fiber isolation eliminates ground potential differences between cabinets up to 3m apart.
- Distributed Energy Resource (DER) management — battery energy storage system (BESS) controllers requiring continuous availability for grid-frequency response; fiber link maintains <10ms failover per IEEE 1547 grid interconnection standards.
Oil & Gas Processing
- Wellhead and pipeline Emergency Shutdown Systems (ESD) — redundant ControlLogix chassis in Class I Division 2 control buildings; 1756-RMC3 fiber link provides intrinsic EMI immunity in environments with variable-frequency drives and high-current motor starters; IEC 61511 / ISA-84 compliance.
- Compressor station control — reciprocating and centrifugal compressor surge control loops requiring bumpless transfer; 3m cable accommodates standard dual-chassis rack spacing in NEMA 4X enclosures.
- LNG terminal loading arm control — redundant PLC architecture for marine loading operations; fiber optic link immune to RF interference from ship-to-shore communication systems.
Water & Wastewater Treatment
- Lift station and pump station control — redundant ControlLogix systems managing submersible pump arrays; 1756-RMC3 maintains synchronization in high-humidity (up to 95% RH non-condensing) underground vault environments.
- Chemical dosing systems — chlorination and fluoridation control requiring continuous operation to meet EPA Safe Drinking Water Act compliance; fiber link eliminates interference from chemical metering pump VFDs.
- SCADA master station redundancy — dual-chassis ControlLogix acting as SCADA front-end processors; 3m fiber cable spans adjacent rack positions in climate-controlled control rooms.
Automotive & Discrete Manufacturing
- Body-in-white welding line control — redundant ControlLogix managing 50–200 robot I/O points; 1756-RMC3 fiber link immune to high-frequency welding EMI (up to 100kHz); ISO/TS 16949 quality system environments.
- Paint shop conveyor control — continuous-process paint lines where a controller fault causes line stoppage and scrap; hot-standby redundancy via 1756-RMC3 eliminates single-point failure; operating temperature range 0–60°C.
- Engine assembly test cells — high-cycle automated test equipment requiring 24/7 availability; fiber optic link provides galvanic isolation between test cell and control room chassis.
Pharmaceutical & Food Processing
- Batch reactor control — FDA 21 CFR Part 11 compliant redundant ControlLogix systems; 1756-RMC3 maintains audit-trail continuity during controller switchover events; cleanroom-compatible fiber cable jacket.
- CIP (Clean-In-Place) system control — redundant PLC managing caustic and acid cleaning cycles; fiber link immune to chemical vapor environments; GAMP 5 validation documentation available.
- Filling and packaging lines — high-speed packaging (300–600 units/min) requiring zero-downtime controller architecture; 3m cable length accommodates standard dual-chassis panel layouts.
Mining & Metals
- Conveyor and hoist control — redundant ControlLogix in underground mining environments; 1756-RMC3 fiber link immune to high-voltage cable EMI from 6.6kV hoist motors; IECEx Zone 2 adjacent installations.
- Smelter process control — aluminum and steel smelting furnace control requiring continuous availability; fiber optic link withstands ambient temperatures up to 55°C and high electromagnetic interference from arc furnaces.
- Ore processing plant — SAG mill and ball mill control systems; redundant chassis linked via 1756-RMC3 in dusty, high-vibration environments; IP54-rated enclosure installations.
Technical Specifications
| Catalog Number | 1756-RMC3 |
| Manufacturer | Allen-Bradley / Rockwell Automation |
| Cable Type | Fiber Optic, Duplex — duplex design carries simultaneous TX/RX synchronization data between both RM modules |
| Cable Length | 3 meters (9.84 ft) — designed for adjacent dual-chassis rack installations within the same enclosure or adjacent panels |
| Compatible Modules | 1756-RM2, 1756-RM2/A — connects the two RM2 modules that form a ControlLogix redundancy pair |
| Connector Type | LC Duplex (both ends) — keyed connectors prevent incorrect insertion; no tools required for field connection |
| Fiber Type | Multimode — sufficient for 3m intra-panel distances; eliminates EMI susceptibility of copper alternatives |
| Operating Temperature | 0°C to 60°C (32°F to 140°F) — covers standard industrial control panel environments |
| Storage Temperature | -40°C to 85°C |
| Relative Humidity | 5% to 95% non-condensing — suitable for high-humidity utility and water treatment installations |
| Weight | Approx. 150 g |
| Series | ControlLogix 1756 |
| Redundancy System | ControlLogix Hot-Standby (SIL 2 capable with appropriate safety configuration) |
Why Engineers Specify This Model
- In turbine governor and ESD applications, the 1756-RMC3 delivers sub-10ms bumpless controller switchover because the dedicated fiber link transmits chassis synchronization data at line speed without competing with process I/O traffic, meeting IEC 61511 SIL 2 availability requirements.
- In high-EMI environments (welding cells, arc furnaces, VFD-dense motor control centers), the 1756-RMC3 delivers zero bit-error synchronization because fiber optic transmission is inherently immune to electromagnetic interference, eliminating the copper-cable noise issues that cause false redundancy faults.
- In multi-cabinet panel layouts, the 1756-RMC3 delivers reliable physical reach because the 3-meter length is engineered to span the standard spacing between adjacent ControlLogix chassis racks without excess cable management complexity.
- In pharmaceutical batch and food processing applications, the 1756-RMC3 delivers audit-trail continuity during switchover because the hot-standby architecture maintains program state and I/O data across the fiber link, satisfying FDA 21 CFR Part 11 and GAMP 5 validation requirements.
- In underground mining and offshore installations, the 1756-RMC3 delivers galvanic isolation between chassis because the fiber medium carries no electrical potential, eliminating ground loop currents that corrupt synchronization signals in facilities with multiple earthing systems.
- In 24/7 continuous process industries (petrochemical, power, water), the 1756-RMC3 delivers zero-downtime controller maintenance capability because the redundancy link allows one chassis to be taken offline for firmware updates or hardware replacement while the other maintains full process control.
Complete System Bill of Materials
The following components form a complete ControlLogix Hot-Standby redundancy system. The 1756-RMC3 is the physical interconnect that makes the entire architecture function.
- 1756-RMC3 (this item) — RM fiber optic cable, 3m; the synchronization link between the two redundancy modules; qty: 1 per redundancy pair
- 1756-RM2 / 1756-RM2/A — ControlLogix Redundancy Module; installed in each chassis (primary and secondary); manages switchover logic and communicates via the 1756-RMC3 fiber link; qty: 2 (one per chassis)
- 1756-L8x / 1756-L7x — ControlLogix L8 or L7 Series CPU; primary and secondary controllers; must be identical catalog numbers and firmware revisions for redundancy compatibility; qty: 2
- 1756-PA75 / 1756-PB75 — ControlLogix Power Supply (AC or DC); one per chassis; redundant power supply configurations recommended for SIL applications; qty: 2+
- 1756-A10 / 1756-A13 / 1756-A17 — ControlLogix Chassis (10, 13, or 17 slot); primary and secondary chassis must be same slot count; qty: 2
- 1756-EN2T / 1756-EN2TR — EtherNet/IP Communication Module; for SCADA/HMI connectivity; 1756-EN2TR recommended for Device Level Ring (DLR) network redundancy; qty: 2+ (one per chassis minimum)
- 1756-IB16 / 1756-OB16E — Digital I/O Modules; process field device connections; I/O modules are installed in the primary chassis and automatically controlled by whichever CPU is active; qty: as required by application
- 1756-IF8 / 1756-OF8 — Analog I/O Modules; for analog process signals (4–20mA, 0–10V); qty: as required by application
Compliance & Industry Standards
- CE Marking (EU) — Issued by Rockwell Automation; confirms compliance with EU EMC Directive (2014/30/EU) and Low Voltage Directive (2014/35/EU); required for installation in European Union facilities and export to EU customers.
- UL Listed / cUL — Underwriters Laboratories; confirms compliance with UL 508 (Industrial Control Equipment); required for installations in North American facilities under NEC and CEC electrical codes.
- RoHS Compliant — EU Directive 2011/65/EU; confirms restriction of hazardous substances (lead, mercury, cadmium, etc.); required for EU market access and preferred by environmentally-governed procurement programs.
- IEC 61131-2 — International Electrotechnical Commission; programmable controller equipment standard; confirms the cable meets environmental and electrical immunity requirements for industrial PLC system components.
- IEC 61511 / ISA-84 Compatible System — When used as part of a properly configured ControlLogix SIL 2 redundancy architecture, the 1756-RMC3 supports Safety Instrumented System (SIS) designs; buyers should reference Rockwell Automation Safety Reference Manual 1756-RM001.
- ATEX / IECEx (Adjacent Installation) — The 1756-RMC3 itself is a standard (non-Ex) component; however, it is routinely installed in control rooms adjacent to ATEX Zone 2 / IECEx Zone 2 classified areas in oil & gas and mining facilities; consult local electrical authority for area classification boundary requirements.
Quality Assurance & Sourcing
Sourcing Channels: Konmask.com sources the 1756-RMC3 exclusively through authorized industrial automation distributors and verified surplus channels with documented chain-of-custody records. We do not source from anonymous spot markets or unverified brokers.
4-Step Inspection Process:
- Physical Authenticity Verification — Label inspection, connector keying check, cable jacket markings, and catalog number validation against Rockwell Automation published specifications.
- Connector Integrity Test — LC duplex connector end-face inspection using fiber optic microscope; ferrule cleanliness and physical damage assessment per IEC 61300-3-35 cleanliness standards.
- Optical Continuity Check — Visual light source continuity test on both fiber strands to confirm unbroken optical path from end to end.
- Packaging & Documentation Review — Original or equivalent ESD-safe packaging confirmed; date codes recorded; available documentation compiled for buyer delivery.
Available Documentation: Certificate of Conformance (CoC) | Material Test Report (on request) | Rockwell Automation Product Certification (downloadable from ra.rockwell.com) | Packing list with serial/date code records | Export compliance documentation (HS code, country of origin)
How to Source This Part
- Submit Your Requirement — Contact us via the product page inquiry form, email support@konmask.com, or WhatsApp/WeChat +0086 19859288691 with your catalog number (1756-RMC3), required quantity, and delivery timeline. We respond within 24 hours on business days.
- Receive Quote & Availability Confirmation — We confirm stock availability, lead time, unit price, and shipping options. For urgent requirements, same-day shipping from our warehouse is available for in-stock items.
- Order, Ship, Receive — We ship globally via DHL Express, FedEx International, and UPS Worldwide. Export documentation (commercial invoice, packing list, certificate of origin) provided for all international shipments. Typical transit: 3–7 business days to most destinations.
Application-Specific FAQ
Q: Can the 1756-RMC3 be used in a SIL 2 Safety Instrumented System for oil & gas ESD applications?
A: The 1756-RMC3 is a component of the ControlLogix redundancy architecture that Rockwell Automation has validated for use in SIL 2 capable systems when configured per the 1756-RM001 Safety Reference Manual. For ESD applications in oil & gas facilities governed by IEC 61511 / ISA-84, the complete system — including the 1756-RM2 modules, CPUs, and this fiber cable — must be configured, validated, and documented by a qualified Functional Safety Engineer. Contact us for access to Rockwell’s SIL certification documentation.
Q: Our power generation plant has two ControlLogix chassis in separate cabinets approximately 2.5 meters apart. Will the 1756-RMC3 reach, and is there a longer version available?
A: The 1756-RMC3 at 3 meters will accommodate a 2.5-meter cabinet separation with 0.5 meters of service loop — sufficient for standard installations. Rockwell Automation also offers the 1756-RMC1 (1 meter) for same-rack installations and the 1756-RMC10 (10 meters) for installations where chassis are in separate enclosures or rooms. Contact us to confirm availability of the appropriate length for your plant layout.
Q: In our automotive welding line, we experience frequent nuisance redundancy faults with our current copper synchronization cable. Will switching to the 1756-RMC3 fiber cable resolve this?
A: Yes — this is one of the most common field issues in high-EMI manufacturing environments. Resistance welding equipment generates broadband electromagnetic interference (typically 1kHz–100kHz) that induces noise on copper signal cables, causing the 1756-RM2 modules to log false synchronization errors and, in severe cases, trigger unnecessary switchover events. The 1756-RMC3 fiber optic cable is completely immune to electromagnetic induction — fiber carries light, not electrical current — eliminating the noise coupling mechanism entirely. Customers in automotive body-in-white and stamping applications consistently report elimination of nuisance redundancy faults after replacing copper links with the 1756-RMC3.
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