Purchase now the Allen-Bradley 1786-BNC — the standard BNC coaxial media tap designed for reliable physical layer connections on Allen-Bradley ControlNet networks.
What Is the Allen-Bradley 1786-BNC?
The 1786-BNC is a ControlNet network media tap manufactured by Allen-Bradley (Rockwell Automation). It provides the physical coaxial connection point — the tap — that links individual ControlNet devices to the main RG-6 coaxial trunk cable of a ControlNet network segment. Every node on a ControlNet coaxial network requires a tap of this type to physically connect to the network, making the 1786-BNC one of the most fundamental infrastructure components in any coaxial ControlNet installation.
Key Technical Specifications
- Product family: ControlNet Media — 1786 series
- Media type: RG-6 coaxial ControlNet trunk cable
- Connector type: BNC (Bayonet Neill-Concelman)
- Network: ControlNet (coaxial media)
- Compatible cable: Allen-Bradley 1786-RG6 and equivalent ControlNet-rated RG-6 coaxial cable
- Tap spacing: Minimum 1 m between taps on the same trunk segment
- Maximum nodes per segment: Up to 48 nodes (per ControlNet specification)
- Termination: Requires 75-ohm terminator (1786-XT) at each end of the trunk
Role in ControlNet Network Architecture
In a ControlNet coaxial network, the physical layer is built around a daisy-chained RG-6 coaxial trunk cable. The 1786-BNC tap connects each device to this trunk without interrupting network continuity. This is a critical distinction from simple inline connectors: the tap allows a device to be physically disconnected without breaking the network segment, which is essential for maintenance and hot-swap operations on live ControlNet systems.
Installation Advice
- Always maintain a minimum distance of 1 metre between consecutive taps on the trunk cable. Taps placed too close together introduce signal reflections that degrade network performance.
- Ensure the trunk cable is properly terminated at both ends with 75-ohm terminators (1786-XT). An unterminated ControlNet segment will produce intermittent communication errors and is a common cause of difficult-to-diagnose network faults.
- When routing the coaxial trunk, avoid running it parallel to high-voltage power cables. Maintain a minimum separation of 200 mm to avoid electromagnetic interference.
- Use only ControlNet-rated RG-6 coaxial cable — standard domestic RG-6 cable does not meet the impedance and loss specifications required for industrial ControlNet installations.
- After installation, use RSNetWorx for ControlNet to perform a network scan and verify all nodes are visible and communicating correctly before commissioning the system.
Maintenance Tips
- Periodically inspect BNC connector bodies for signs of corrosion, especially in humid or chemically aggressive environments. Corroded BNC connectors are a leading cause of intermittent ControlNet faults.
- Check that the BNC locking mechanism (bayonet lock) is fully engaged on all connections. A partially locked BNC can cause signal loss that is extremely difficult to trace.
- During scheduled maintenance windows, use a ControlNet network analyser to check signal amplitude and reflections across the trunk — early detection of degrading taps avoids unplanned downtime.
Frequently Asked Questions
Q: Can the 1786-BNC tap be used on a live ControlNet network without shutting it down?
A: Adding a new tap to a live ControlNet trunk is not recommended, as it requires cutting the coaxial cable to insert the tap, which interrupts network continuity. Plan tap installations during scheduled maintenance windows. However, connecting or disconnecting a device from an existing installed tap can be done without network disruption.
Q: How many 1786-BNC taps can be installed on a single ControlNet coaxial segment?
A: A maximum of 48 nodes are supported per ControlNet coaxial segment, with a minimum tap spacing of 1 metre and a maximum trunk length of 1,000 metres at standard ControlNet data rates.
Q: Is the 1786-BNC compatible with ControlNet fibre optic media?
A: No. The 1786-BNC is exclusively for coaxial RG-6 ControlNet media. For fibre optic ControlNet installations, Allen-Bradley provides separate fibre media components within the 1786 product family.
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