Technical bulletin
Technical bulletin: surge protection on RS-485 and LAN lines at field gateways
Two 2026 jobs at a Jambi fuel terminal show why the gateway between field devices and SCADA or TMS needs surge protection on both its RS-485 and its Ethernet side.
- Technical bulletin
- Type
- Technical bulletin
- Published
- 13 November 2026
- Location
- Jambi
- Reading time
- 4 min
A surge is a short, high-voltage transient that enters equipment through its cables, for example from lightning induction or from switching of electrical equipment. A surge protection device (SPD) diverts that energy before it reaches the electronics it guards.
This bulletin draws on two Citia jobs at a fuel terminal in Jambi in 2026: the replacement of the ATG gateway between the automatic tank gauges (ATG) and the tank management system (TMS), and the MOV communication restoration between motor-operated valves and SCADA. Both paths use the same gateway model, an Advantech ECU-1051.
Field device on a long RS-485 run.
Hover, focus or tap a step to read its note.The problem in the field
On the ATG side, data between the gauges and the TMS was faulty or unstable, and tank data could not be read in real time. The project page names the exposure plainly: the gateway was open to electrical disturbance from the field lines, and both the RS-485 Modbus and the LAN Ethernet lines could be hit by surges from lightning or electrical short circuits. Because the gateway is the only bridge, its failure cut the whole data link to the monitoring system.
On the MOV side, the restored design already places an SPD on the RS-485 line before the gateway and a LAN arrester between the gateway and SCADA, giving both main communication lines a protection layer.
| Criterion | RS-485 SPD | LAN arrester |
|---|---|---|
| Placed on | Serial line from the field, before the gateway | Ethernet line between the gateway and the network |
| Protects | RS-485 port of the gateway and the line | Ethernet port, switch and SCADA or TMS computer |
| Typical source of surge | Lightning induction on long field cables | Overvoltage entering through the Ethernet cable |
Detection and prevention
Watch for the symptom
Data that drops out or freezes in SCADA or TMS for every device behind one gateway points at the gateway or its lines first.
Check both sides
Test the RS-485 link from the devices to the gateway and the LAN link from the gateway to the application network.
Protect both lines
Fit an SPD on the RS-485 line and a surge protector on the LAN line, from the start in lightning-prone areas.
Test end to end
After a replacement, confirm data from the field device reaches the application, and that a SCADA command returns MOV feedback.
Surge protection works with good grounding, not in place of it. The Texas Instruments RS-485 Design Guide covers grounding and galvanic isolation for nodes with different ground potentials, and its note on IEC 61000-4-x tests explains the lightning and surge immunity test in IEC 61000-4-5. For the wider fault-finding routine on serial lines, see the Citia guide on Modbus RS-485 troubleshooting.
Common questions
Why does a Modbus RS-485 gateway need surge protection?
Because long field cables can carry surges from lightning induction or electrical switching straight into the gateway port. At Jambi a failed gateway cut all ATG data to the TMS.
Is an SPD on RS-485 enough?
No. The Ethernet side can also carry overvoltage, so the Jambi jobs added a LAN arrester or LAN surge protector between the gateway and the network.
What test should follow a gateway replacement?
An end-to-end test: data from the field device must appear in the application, and for valves a command from SCADA must return the matching MOV feedback.
Sources and further reading
- Jambi fuel terminal: replacement of ATG gateway (ECU) spare part (opens in a new tab)
- Motor-operated valve (MOV) communication (opens in a new tab)
- The RS-485 Design Guide (SLLA272D) (opens in a new tab)
- IEC 61000-4-x Tests for TI's Protection Devices (SLVA711) (opens in a new tab)
- Cover photo by Tony Webster from Minneapolis, Minnesota, United States, CC BY 2.0 (cropped and colour graded) (opens in a new tab)
Next step
Discuss a similar need at your facility.
Tell us about the equipment and the process. The Citia team answers with technical context.
Related products and solutions
- KnowledgeIndustrial IoT gateways and telemetry: getting remote-site data to a dashboardAn industrial IoT gateway reads field devices, buffers data when the network drops and sends it to a server. How telemetry differs from SCADA and how to choose a gateway.
- ProjectJambi fuel terminal: replacement of ATG gateway (ECU) spare partThis project replaced the spare part Gateway ATG ECU-1051 Advantech at the Jambi fuel terminal to restore data communication between the Automatic Tank Gauging (ATG) and the Tank Management System (TMS) application.
- ProjectMotor-operated valve (MOV) communicationRestoration of Flowserve Limitorque MOV communication to InduSoft SCADA at Fuel Terminal Jambi, through RS-485, an SPD, an ECU-1051 gateway and a LAN arrester.
- KnowledgeTroubleshooting Modbus RS-485 communicationMost Modbus RS-485 faults start at the physical layer. A field checklist for termination, biasing, topology, grounding, serial settings and exception codes.
- ProductINTEGRA TMSCollects ATG readings from every tank for live levels, history, tank tickets and stock posting to SAP.
- WebinarMOV not read in SCADA? Practical troubleshooting from gateway to field deviceCitia Micro-Webinar #03, Friday 21 November 2026 at 14.00 WIB on Microsoft Teams: a free 20-minute case study on MOVs that SCADA cannot read.