Description

Technical Specifications

Parameter Name	Parameter Value
Product Model	1756-CNBR
Manufacturer	Allen-Bradley / Rockwell Automation
Product Type	ControlNet Redundant Bridge Module
ControlNet Connectors	2 × BNC (redundant media)
Network Access Port	1 × NAP (RJ-45, 8-pin shielded)
Cable Type	Quad shield RG-6 coaxial
Communication Rate	5 Mbps
Maximum Nodes	99
Maximum Connections	64 (40–48 recommended for optimal performance)
Backplane Current (5.1V DC)	970 mA
Backplane Current (24V DC)	1.7 mA
Power Dissipation	5.14 W
Thermal Dissipation	17.5 BTU/hr
Isolation Voltage	50V continuous; tested to 500V AC for 60 seconds
Operating Temperature	0…60 °C (32…140 °F)
Slot Width	1
Weight	Approximately 0.293 kg (0.64 lb)

Main Features and Advantages

Redundant ControlNet media for fault-tolerant communication: The defining characteristic of the 1756-CNBR is its dual BNC connector configuration, which allows connection to two identical ControlNet links. In a redundant media topology, the module transmits and receives on both channels simultaneously; if one trunkline or tap is severed or disconnected, communication continues uninterrupted over the healthy channel . This capability is essential in continuous-process applications where a network fault must not translate into a production stoppage.

Native integration with ControlLogix redundancy systems: The 1756-CNBR is the specified ControlNet module for use in ControlLogix redundant chassis pairs. Rockwell’s redundancy guidelines identify the 1756-CNBR as a required component for redundant ControlNet media configurations, and the module’s firmware and diagnostic behavior are optimized for the switchover timing and connection management demands of redundant controller architectures . When planning a redundant system, Rockwell recommends allocating two consecutive ControlNet node addresses for each pair of 1756-CNBR modules across the primary and secondary chassis .

Diagnostic visibility and network management: The 1756-CNBR includes a four-character diagnostic display that provides real-time status information for troubleshooting network issues . This on-module display, combined with RSNetWorx for ControlNet scheduling and diagnostic tools, gives maintenance personnel the visibility needed to identify cable faults, node conflicts, and connection failures without requiring a programming terminal at the cabinet.

Application Field

The 1756-CNBR is deployed in ControlLogix installations where ControlNet communication must remain available despite physical damage to network cabling or the failure of a single network segment. In process industries—including oil and gas, chemical, and power generation—the 1756-CNBR is used in redundant ControlLogix chassis pairs to connect primary and secondary controllers to distributed I/O over redundant ControlNet media. The module’s ability to maintain communication across a severed trunkline directly supports the high-availability requirements of continuous production assets where unplanned shutdowns carry severe financial and safety consequences .

In manufacturing plants running ControlLogix-based production lines, the 1756-CNBR serves as the bridge between the local chassis and remote I/O drops or peer controllers on the ControlNet network. Its dual-port redundancy is particularly valuable in installations where ControlNet cabling traverses physically active areas—such as assembly lines, material handling systems, and packaging equipment—where cable damage from moving machinery or human activity is a realistic risk. The 1756-CNBR is also found in infrastructure applications such as water treatment and wastewater facilities, where ControlNet networks span large plant footprints and communication reliability is critical for pump, valve, and process control. For systems that require the determinism and scheduled messaging capabilities of ControlNet, the 1756-CNBR provides the redundant communication path that keeps the control system operational when the primary media path is compromised.