Electric vehicle (EV) adoption is accelerating worldwide, driven by consumer demand, government incentives, and ambitious sustainability goals. Alongside this growth comes an equally rapid expansion of EV charging infrastructure, from residential wall units to high-power public DC fast chargers.

To keep pace, electric vehicle supply equipment (EVSE) must deliver not only faster charge times but also the highest levels of safety, reliability, and efficiency — often in outdoor environments exposed to weather, grid fluctuations, and frequent user interaction. One of the most persistent challenges in these settings is the occurrence of transient events: brief but potentially destructive electrical disturbances that can damage sensitive electronics, interrupt service, and shorten equipment lifespan.

Protecting EV chargers against these events requires a robust mix of overvoltage and overcurrent safeguards, paired with precise current sensing for fault detection and system control. In this post, we’ll explore how Bourns’ solutions — ranging from IsoMOV® hybrid protectors to high-performance fuses, shunt resistors, and rugged Riedon® precision resistors — equip EVSE designs to withstand transient stresses while maintaining long-term operational stability.

Understanding Transient Events in EV Charging Infrastructure

Transient events are short-duration surges in voltage or current that can occur in any electrical system, but they are especially common in EV charging environments. Unlike steady-state overloads, these spikes happen in microseconds to milliseconds, yet they can deliver enough energy to damage or degrade sensitive electronics.

In EV charging infrastructure, transient events often originate from multiple sources: a lightning strike near the facility, grid switching during power distribution, the sudden connection or disconnection of a vehicle, or even electrostatic discharge (ESD) from a user’s interaction with charging equipment. High-power outdoor installations such as Level 2 and Level 3 EVSE are particularly vulnerable, as they operate at elevated voltages and currents while remaining exposed to environmental and grid-related disturbances.

Over time, repeated transients can erode insulation, stress power components, and cause intermittent or catastrophic failures. Designing solutions to these issues through surge and overcurrent protection is a foundational element of EVSE engineering. To that end, recognizing the causes and frequency of these events is the first step in designing chargers that can reliably withstand them.

Overview of Surge and Overcurrent Protection Strategies

EV chargers require a two-pronged approach to electrical protection: one to handle sudden overvoltage conditions, and another to stop damaging overcurrent events. Overvoltage protection devices like metal oxide varistors (MOVs), gas discharge tubes (GDTs), and other clamping technologies work by diverting or absorbing excess energy before it can reach sensitive circuits. These are critical for mitigating lightning-induced surges, grid switching spikes, and electrostatic discharges.

Overcurrent protection, by contrast, focuses on interrupting dangerous fault currents that can cause overheating, fire hazards, or catastrophic component failure. This is achieved using fuses, circuit breakers, or polymeric positive temperature coefficient (PPTC) devices that shut down the fault path quickly and safely.

Across the industry, there is a push toward multi-functional and space-saving components that combine these protection modes or deliver enhanced performance in smaller footprints. This reduces the complexity of charger designs, helps optimize internal space, and simplifies compliance with safety standards — all without sacrificing protection performance.

Bourns^® IsoMOV^® Hybrid Protectors – Advanced Overvoltage Protection  for EV Charging Infrastructure

The Bourns® IsoMOV® hybrid protectors represent a new class of overvoltage protection devices, combining the fast response of a metal oxide varistor (MOV) with the isolation benefits of a gas discharge tube (GDT) in a single compact package. This hybrid design reduces leakage current, enhances surge-handling capability, and provides longer service life compared to conventional MOV-only solutions.

In EV charging infrastructure, IsoMOV® hybrid protectors are ideally suited for AC line circuit protection, where repeated surges and transients are common. By absorbing high-energy pulses without degrading prematurely, they help maintain uptime and reduce costly maintenance cycles.

From Level 1 residential chargers to high-power Level 3 DC fast charging stations, IsoMOV® devices can be deployed at the input stage to shield the rest of the system (controllers, power supplies, and communication modules) from damaging overvoltage conditions. This not only protects the investment in sensitive electronics but also supports compliance with international safety and surge immunity standards.

Bourns® Fuses: The First Line of Defense for Overcurrent Protection

Overcurrent events — whether caused by short circuits, component failures, or external faults — pose a serious threat to EV charging equipment. Without a robust first line of defense, these conditions can lead to overheating, fire hazards, or catastrophic equipment damage.

Bourns offers a comprehensive fuse portfolio designed to interrupt fault currents quickly and safely, minimizing the risk of damage to downstream circuitry. Options include fast-acting fuses for sensitive electronics, time-delay fuses for inrush-current tolerance, and high-voltage/high-current designs capable of handling the demands of both AC and DC stages in EVSE systems.

Strategic placement of Bourns® fuses, such as at the AC input stage and within the onboard power conversion block, ensures faults are isolated before they propagate, protecting power modules, relays, and control boards. These fuses are built to meet the voltage, current, and endurance requirements of modern EVSE, providing dependable performance in both indoor and outdoor charging environments.

Current Sensing with Bourns

Accurate current measurement is critical in EV charging stations for functions such as billing, load management, fault detection, and ensuring safe charge cycles. Precision resistors are the backbone of these sensing systems, converting current flow into readable voltage signals for control and monitoring electronics.

Bourns® shunt resistors offer a broad selection of power ratings, resistance values, and package sizes to match the needs of different EVSE architectures. Engineered for high stability and excellent pulse-handling capability, these shunts deliver consistent performance over time — even under the high transient loads typical in fast charging.

For applications requiring exceptional ruggedness, Riedon® resistors by Bourns bring decades of expertise in wirewound technology. These resistors excel in outdoor and high-temperature environments, making them ideal for critical subsystems that must remain stable despite wide temperature swings or continuous heavy loads. Together, Riedon® resistors by Bourns provide a complete current-sensing portfolio for reliable, real-time monitoring in Level 1 through Level 3 EVSE systems.

Real-World Application Scenarios

Consider a Level 3 DC fast charger designed to deliver up to 350 kW. At the AC line input, a Bourns® IsoMOV® hybrid protector is installed to shield the system from lightning-induced surges and grid-switching transients. This single component combines MOV and GDT functionality, delivering robust overvoltage protection with reduced leakage current.

Downstream, high-voltage Bourns® fuses safeguard the power conversion stage, isolating faults quickly to prevent catastrophic damage to converters and inverters. For accurate energy delivery and fault detection, Bourns® shunt resistors measure current in real time, feeding precise data to the charger’s control system for load balancing and safety shutoffs. In parallel, Riedon® wirewound resistors by Bourns provide stable, high-power resistance in ruggedized subsystems, ensuring continued reliability even in outdoor, high-temperature installations.

The result is a charging platform with improved fault isolation, reduced downtime, and enhanced safety that’s capable of meeting today’s demanding EVSE performance and compliance requirements.

Why Choose Bourns for EV Charging Protection and Current Sensing?

With AEC-Q and UL-compliant options, Bourns® products meet stringent automotive and safety standards, ensuring compatibility with global regulatory requirements. Compact, integration-friendly footprints help engineers by saving valuable board space while reducing assembly complexity. 

Bourns brings decades of proven expertise in circuit protection and current sensing to the rapidly evolving EVSE market, delivering engineers the ability to protect and monitor critical EVSE systems — today and into the future. 

Contact an expert to find the protection for your project.