PLC & SCADA Surge Protection
SCADA and PLC systems are the control layer of every modern water and wastewater facility. When a transient voltage event reaches that layer, the first indication is not always damaged equipment. It is often lost visibility: remote alarms stop reporting, communications fail, and operators lose insight into what is happening across the facility.
Effective SCADA surge protection and PLC surge protection from DEHN focus on every electrical pathway into the control system, not just the incoming power feed. DEHN helps utilities protect the power, communication, signal, and instrumentation pathways that support reliable automation and operational visibility.
What Is a Surge Protective Device?
A surge protective device— SPD — is designed to limit transient overvoltages by diverting excess energy safely to ground before it reaches sensitive electrical or electronic equipment.
In industrial control systems, SPDs are installed on power circuits, communication networks, and instrumentation circuits to help reduce the risk of equipment damage, nuisance faults, and communication failures caused by lightning, utility switching, motor starts, VFD operation, or other switching events.
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How Surges Reach SCADA and PLC Systems
Protecting the service entrance alone does not protect the control system. Transients can enter through multiple pathways, many of which terminate directly at sensitive automation equipment.
Common surge paths include:
- Incoming AC power supplying control panels
- Analog signal loops, including 4–20 mA circuits connecting field instruments to PLC I/O cards
- Industrial communication networks such as Modbus, Profibus, and Industrial Ethernet
- Remote I/O and telemetry connections
- Ground potential rise during nearby lightning events
A comprehensive surge protection strategy for control systems considers every pathway capable of carrying transient energy into the automation network.
Why I/O Cards Are Often the First Point of Failure
An input/output— I/O — card is the interface between the PLC and the field devices it monitors and controls. Every level transmitter, pressure sensor, flow meter, valve, and motor feedback signal ultimately passes through an I/O card before reaching the controller.
Because these cards connect directly to field wiring, they are among the most exposed components in the control system.
Proper I/O card surge protection helps reduce the likelihood that a transient on a single field circuit will disable an entire process loop. It also helps avoid extended downtime when replacement cards have long procurement lead times or require controller reconfiguration before the process can return to service.
Coordinated Surge Protection Requires More Than One SPD
No single SPD can effectively protect an entire electrical distribution or control system. Water and wastewater facilities rely on coordinated protection at multiple locations, with each device managing surge energy appropriate for its installation point.
Each protection stage reduces the transient energy passed to the next, improving the performance of the overall system.
A typical protection architecture includes:
Type 1 SPD
Typical Installation
Service entrance
Primary Function
Handles high-energy surges entering from the utility or lightning events before they reach facility distribution equipment.
Type 2 SPD
Typical Installation
Distribution and control panels
Primary Function
Limits residual surge energy before it reaches downstream electrical equipment.
Type 3 SPD
Typical Installation
Sensitive electronic equipment
Primary Function
Provides localized protection for PLCs, communication devices, instrumentation, and other electronic systems.
Protecting More Than the Control Panel
SCADA reliability depends on more than the PLC cabinet. Remote pump and lift stations, instrumentation, communication equipment, telemetry panels, and field devices all require protection appropriate to their electrical connections.
For a coordinated protection approach, utilities should evaluate:
- SCADA and PLC panels
- RTUs and telemetry equipment
- Pump and lift station control panels
- VFDs and motor control equipment
- Level, flow, and pressure instrumentation
- Communication and signal circuits
- Grounding and bonding pathways
Identify SCADA Exposure at Pump and Lift Stations
Pump and lift stations are common points of SCADA visibility loss because they combine remote telemetry, exposed communications, VFDs, instrumentation, and utility power in one control panel.
A Pump/Lift Station Surge Risk Assessment from DEHN helps identify exposed power, communication, grounding, bonding, and instrumentation pathways that may contribute to recurring SCADA outages, VFD trips, telemetry failures, and unplanned downtime.
Ask About a Pump/Lift Station Surge Risk AssessmentDownload the Water & Wastewater Protection Toolkit
The DEHN Water & Wastewater Lift & Pump Station Controls & Telemetry Resilience Toolkit includes an electrical pathway audit checklist, transient pathway map, and engineering guidance to help identify where surge protection should be incorporated throughout a facility.
Download the ToolkitFrequently Asked Questions
What is a Type 1 SPD?
A Type 1 SPD is installed at the electrical service entrance to help protect a facility from high-energy surges originating from the utility or lightning events before they enter the building's electrical distribution system.
Can a Surge Damage a PLC Without Destroying It?
Yes. A transient event may not permanently damage the PLC but can cause communication failures, processor faults, unexpected resets, corrupted I/O signals, or intermittent equipment behavior that is difficult to diagnose.
What Is an I/O Card and Why Does It Fail From Surges?
An I/O card connects field devices to the PLC. Because it interfaces directly with wiring that extends throughout the facility, transient voltages entering those circuits can reach the card unless appropriate surge protection is installed.
What Is a Coordinated SPD System?
A coordinated SPD system uses multiple surge protective devices installed at different locations—typically Type 1, Type 2, and Type 3 SPDs—to progressively reduce transient energy before it reaches sensitive electrical and control equipment. Each protection stage performs a different role, creating a more effective protection strategy than a single SPD alone.