Distribute and Protect Your Network with the 990NAD23000 Junction Box

Technical Specifications

Main Features and Advantages

The Schneider 990NAD23000​ junction box offers a set of practical features that directly address the common installation and reliability challenges of Modbus Plus networks. Its most significant advantage is the provision of a centralized, professional connection point. This eliminates the need for field technicians to cut into the main trunk cable to make a connection, a practice that often leads to poor connections, compromised cable shielding, and difficult-to-diagnose intermittent faults. Instead, the trunk cable runs continuously through the 990NAD23000, and the device is connected via a dedicated drop terminal. This “tap” method preserves the integrity of the main trunk and makes adding or removing a node a clean and simple process.Integrated network termination is another critical feature. The Schneider 990NAD23000​ includes a built-in, switchable 120-ohm terminating resistor. Proper termination at both physical ends of a Modbus Plus network segment is non-negotiable for reliable high-speed (1 Mbps) data transmission, as it prevents signal reflections. This integrated resistor ensures termination is always available and correctly installed at the junction box location when needed. The rugged screw terminal blocks ensure a gas-tight, vibration-resistant connection that is far more reliable than insulation displacement connectors (IDCs) or temporary clips. The DIN-rail mountable design allows for neat and organized installation inside control panels alongside other devices. By using the Schneider Electric 990NAD23000, installers enforce best practices in network wiring, resulting in a more stable network with fewer communication errors, easier fault isolation, and reduced maintenance downtime, ultimately protecting the integrity of the entire control system.

Application Field

The Schneider 990NAD23000​ is deployed wherever a robust and reliable Schneider Modbus Plus network is implemented to interconnect automation assets. In discrete manufacturing, such as automotive assembly or packaging lines, the 990NAD23000​ is used to connect multiple Modicon Quantum or Momentum PLCs, Magelis HMIs, and Altivar variable speed drives on a single network, facilitating the high-speed exchange of control and data signals between cells. The junction box is typically installed in the main control panel of each cell or machine, providing the clean connection point to the network trunk that runs along the production line.In process industries like Water/Wastewater Treatment and Chemical Processing, Modbus Plus networks are used for distributed control across large sites. Here, the Schneider 990NAD23000​ is essential for connecting PLCs in remote pump houses, control rooms, and analyzer shelters back to a central SCADA system. Its robust terminal connections are crucial in environments subject to vibration or temperature fluctuations. The junction box is also fundamental in Building Management Systems (BMS) for large facilities like hospitals or airports, where it helps network controllers managing HVAC, lighting, and power. In any application, the Schneider 990NAD23000​ serves as the reliable “network outlet” that ensures each device can be cleanly and correctly integrated into the communication backbone, supporting the deterministic data exchange required for synchronized and efficient industrial operations.

Related Products

• 990NAD21100 or 990NAD21120: Common Modbus Plus network interface cards (NIMs) for Modicon Quantum or other Schneider PLCs, which connect to the network via a junction box like the 990NAD23000.
• 990NAD12800: A Modbus Plus repeater, used to extend the distance of a network segment or connect segments, often used in conjunction with junction boxes.
• 990NAD25600: A Modbus Plus cable tester, a vital tool for commissioning and troubleshooting networks built with components like the 990NAD23000.
• Belden 9841 / 9842: The industry-standard shielded, twisted-pair cable used for the Modbus Plus trunk and drop connections to the 990NAD23000.
• Schneider TCM: A Terminating Connector Module, an alternative simple termination plug, whereas the 990NAD23000​ provides termination plus a junction point.
• 990NAD24900: A potential alternative model junction box or a related connectivity accessory in the Modbus Plus catalog.
• Modicon Momentum 171CCC9xxxx: A popular I/O controller that often uses Modbus Plus for peer-to-peer or SCADA communication, connected via a 990NAD23000.
• TSX SCP 114: A Modbus Plus communication module for the older Modicon TSX Micro/ Premium PLCs, a typical device connected via this junction box.

Installation and Maintenance

Pre-installation preparation: Before installing the Schneider 990NAD23000, carefully plan the network topology, identifying the location of each device (node) and the two ends of the network trunk where termination must be applied. Ensure you have the correct shielded, twisted-pair cable (e.g., Belden 9841). Power down all devices on the Modbus Plus network segment if possible. Mount the 990NAD23000​ junction box securely on a DIN rail inside the device’s control panel. Determine if this particular 990NAD23000​ will serve as a network terminator (it will be at one physical end of the trunk) and note the setting of the termination switch (usually ON for terminator, OFF for pass-through).Maintenance recommendations: The Schneider 990NAD23000​ is a passive device with no moving parts, requiring minimal maintenance. The primary maintenance activity involves periodically checking the tightness of the screw terminal connections, especially in environments with significant vibration or thermal cycling, as loose connections are a leading cause of network issues. Visually inspect for any signs of corrosion or damage. If network communication problems occur, the 990NAD23000​ is a key point for testing: verify the termination switch is correctly set (ON only at the two ends of the trunk, OFF for all intermediate nodes) and use a cable tester to check for continuity, shorts, and proper impedance from the junction box. When adding a new device to an existing network, the 990NAD23000​ makes the process straightforward—simply connect the new drop cable to the junction box’s dedicated terminals without disturbing the main trunk. Always document the network layout, including the location and termination status of each 990NAD23000, for future troubleshooting reference.