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In industrial facilities, power plants, and distribution networks, RTU and PLC devices are fundamental components of critical communication infrastructure.
However, there is a common problem frequently encountered in the field that often remains unresolved and continues to recur:
RS485 port failures and burnouts
These failures are generally caused by:
Since RTUs are expensive and critical devices, such failures result in both high costs and prolonged system downtime.
Explore, step by step, how to protect the most vulnerable communication interfaces of RTUs and PLCs against lightning, ground potential differences, and industrial voltage transients.
In industrial facilities, power plants, and distribution networks, RTUs and PLCs form the core of critical communication infrastructure. Nevertheless, one recurring problem often remains unresolved: RS485 port failures and burnout.
Nearby or direct lightning strikes can generate high-voltage transients in long field cables.
Potential differences between separate panels and field locations can be transferred onto the communication line.
Switching operations and the start-up of large motors can generate sudden voltage transients.
Long RS485 cables can pick up electromagnetic interference and conduct it towards connected devices.
RS485 uses differential signalling; however, in many devices, the line reference is connected to the internal circuit ground. When long field cables interconnect locations with different ground potentials, surge energy can reach the communication transceiver directly.
Devices on the network stop responding, interrupting data transmission and remote monitoring.
Surge energy may affect not only the communication port but also the stability of the power supply and processor.
Damage to the communication transceiver may cause the entire RTU or PLC to stop operating.
Without galvanic separation between the RS485 line and the RTU’s internal circuitry, an electrical path remains through which transient energy can enter the device.
The long-term solution is to establish an electrical barrier between the communication line and the device.
Improved grounding and appropriate surge protection are integral parts of system design; however, galvanic isolation provides a separate layer of protection.
Inotel ISOCON is a communication isolation device designed to electrically isolate the RS485 ports of RTUs, PLCs, and other critical equipment from field cabling.
| Isolation | 2.5 kV |
| Baud Rate | 4 Selectable Rates |
| Mounting | DIN Rail |
| Power Supply | 18–30 V DC |
| Isolation | 2.5 kV |
| Baud Rate | 4 Selectable Rates |
| Mounting | DIN Rail |
| Power Supply | 18–30 V DC |
Suitable for direct integration with RTU models equipped with an RJ45 RS485 port.
Connect the long RS485 cable to the field side of the ISOCON.
The field side and device side are electrically isolated from each other at 2.5 kV.
Ground transients are prevented from reaching the internal circuitry of the RTU or PLC.
Modbus data transmission is maintained while the risk of port failure is reduced.
Power distribution infrastructures in which multiple field locations communicate with a central control system.
Communication networks connecting inverters, meters, and peripheral devices across large sites.
Power generation sites exposed to significant lightning and electromagnetic disturbances.
Communication networks exposed to frequent switching operations and the operation of large motors.
Long-distance cables that interconnect equipment with different ground references.
Automation systems that exchange data between multiple field panels.
ISOCON is not an alarm device. Instead of generating a notification after a fault occurs, it is designed to help prevent the fault by establishing a protective isolation layer between the RS485 line and the critical device.
Protection Objectives
RTU port protection · PLC communication protection · Modbus line protection · RS485 surge and transient protection · Isolation against ground potential differences
RS485 port failures occur frequently, are often insufficiently investigated, and can result in substantial replacement costs. Galvanic isolation is a fundamental layer of a robust, long-term protection strategy for RTU and PLC communication systems.
Example of an ISOCON and RTU installed on a DIN rail inside a field control panel.