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Explore how to protect the most vulnerable communication point of RTU and PLC devices against lightning, ground potential differences and industrial voltage transients.
In industrial facilities, power plants and distribution networks, RTU and PLC devices sit at the centre of critical communication infrastructure. Yet one recurring field problem is rarely solved permanently: RS485 port failures and burnouts.
Nearby or direct strikes create high-energy transients on long field cables.
Potential differences between panels and field points travel along the communication line.
Switching operations and large motor starts generate sudden voltage events.
Long RS485 lines collect electromagnetic disturbances and carry them to the device.
RS485 uses differential signalling, but the line reference is often related to the internal device ground. When long field cables connect different grounding points, transient energy can reach the communication transceiver directly.
Network devices no longer respond, interrupting data flow and remote monitoring.
Transient energy may affect power and processor stability as well as the port itself.
Damage to the transceiver can make the entire RTU or PLC non-operational.
Without galvanic separation between the RS485 line and internal RTU circuitry, an electrical path for transient energy still exists.
The durable solution is to create an electrical boundary between the communication line and the device.
Improved grounding and suitable surge protection remain important, while galvanic isolation provides a distinct protection layer.
Inotel ISOCON is a communication isolation device designed to electrically separate the RS485 ports of RTUs, PLCs and similar critical equipment from field cabling.
| Isolation | 2.5 kV |
| Baud rate | 4 options |
| Mounting | DIN rail |
| Supply | 18–30 V DC |
| Isolation | 2.5 kV |
| Baud rate | 4 options |
| Mounting | DIN rail |
| Supply | 18–30 V DC |
Suitable for direct integration with RTUs using an RJ45-based RS485 port.
Terminate the long RS485 cable on the field side of ISOCON.
Separate the field and device sides by up to 2.5 kV.
Prevent ground disturbances from entering RTU or PLC circuitry.
Protect Modbus data flow and reduce the risk of port failure.
Energy networks where multiple field locations communicate with one control centre.
Widely distributed inverter, meter and peripheral communication networks.
Generation sites exposed to lightning and electromagnetic disturbances.
Communication networks affected by switching operations and large motors.
Long cable runs connecting equipment with different ground references.
Automation projects exchanging data between multiple field panels.
ISOCON is not an alarm device. Rather than reporting a failure after it occurs, it creates a protective isolation layer between the RS485 line and the critical device to help prevent the failure.
Protection objectives
RTU port protection · PLC communication protection · Modbus line protection · RS485 surge and transient protection · Ground-potential isolation