How to Choose the Right Thermal Protector for EV Chargers & Charging Guns

Quick Answer

Selecting the right thermal protector for an EV charger or charging gun requires more than choosing a nominal trip temperature. Engineers should evaluate the protected component, normal operating temperature, maximum ambient temperature, temperature rise, electrical load, response characteristics, reset behavior, installation space, and applicable certification requirements.

Thermal protection may be required at different locations within an EV charging system, including charging guns, cable assemblies, relays and contactors, transformers, power modules, cooling fan motors, and other temperature-sensitive components. The appropriate protection method depends on the thermal behavior and safety requirements of each application.

For OEM and ODM EV charger manufacturers, the selection process should generally follow this sequence:

Application → Protected component → Operating temperature → Maximum ambient temperature → Temperature rise → Allowable temperature → Trip/reset characteristics → Electrical rating → Mechanical integration → Certification → Thermal validation

This guide explains how to select thermal protectors for EV chargers and charging guns, compare different thermal protection technologies, avoid common design mistakes, and prepare the technical information required for a customized thermal protection solution.

Why Do EV Chargers Need Thermal Protection?

EV charging equipment operates under sustained electrical loads, particularly during long charging sessions and high-power DC charging. Electrical resistance, switching losses, semiconductor losses, transformer losses, and insufficient heat dissipation can all contribute to temperature rise.

Typical heat-generating components include:

· High-current conductors

· Charging connectors

· Charging cables

· Relays and contactors

· Power semiconductors

· Transformers

· Charging sockets

· Power inductors

· Internal wiring

· Cooling fan motors

The basic relationship is straightforward: when electrical current passes through resistance, heat is generated. Even a relatively small increase in contact resistance can become significant under high-current operating conditions.

Overheating can lead to:

· Insulation aging

· Connector deformation

· Increased contact resistance

· Reduced component life

· Relay or contactor failure

· Semiconductor damage

· Charging interruption

· Increased maintenance requirements

· Potential safety hazards

Thermal protection is therefore one part of a broader EV charging safety strategy.

Depending on the system architecture, thermal protection may combine:

· Mechanical thermal protectors

· NTC or PTC temperature sensors

· Charger control software

· Cooling systems

· Overcurrent protection

· Thermal fuses

· Other hardware-level safety mechanisms

A thermal protector is particularly useful when an independent hardware-level temperature response is required.

Where Are Thermal Protectors Used in EV Chargers?

Not every component in an EV charger requires the same type of thermal protection. The appropriate device depends on where heat is generated, how quickly the temperature changes, the allowable temperature of the component, and the consequences of overheating.

Typical installation locations include:

A single thermal protector is not necessarily sufficient for a complete charging system. Different components may have different thermal limits and heat-up rates.

1. Thermal Protection for EV Charging Guns

The charging gun is one of the most important locations to consider because it combines high electrical current, compact mechanical construction, and direct user interaction.

During charging, heat may develop around connector contacts because of:

· Contact resistance

· Repeated insertion and removal

· Connector wear

· Oxidation or contamination

· Loose electrical connections

· High charging current

· Elevated ambient temperature

If connector temperature becomes excessive, possible consequences include:

· Housing deformation

· Loss of contact pressure

· Increased electrical resistance

· Accelerated connector aging

· Charging interruption

· Excessive surface temperature

· Safety concerns for users

For this reason, some charging gun designs incorporate temperature sensing and/or dedicated thermal protection close to the potential hot spot.

What Should Be Considered When Selecting a Charging Gun Thermal Protector?

The key factors include:

Why Miniature Thermal Protectors Are Often Considered

Charging guns have limited internal space. A large thermal protector may interfere with the connector, wiring, housing, or insulation structure.

Miniature thermal protectors can provide:

· Compact dimensions

· Low thermal mass

· Easier integration

· Suitable thermal response

· Flexible lead-wire configurations

However, the actual selection should be validated using the charging gun's measured temperature profile rather than based on size alone.

2. Thermal Protection for EV Charging Cables

Charging cables can carry high current continuously during charging sessions. Their temperature is influenced not only by electrical current but also by environmental and installation conditions.

Important factors include:

· Charging current

· Cable conductor size

· Ambient temperature

· Cable length

· Cable routing

· Cable coiling

· Ventilation

· Charging duration

· Conductor resistance

· Connector temperature

A cable that operates safely under laboratory conditions may experience substantially higher temperatures when installed in a high-ambient-temperature environment or under restricted heat dissipation conditions.

Thermal protection or temperature sensing may therefore be incorporated near cable terminations or other locations where temperature monitoring is required.

The objective is not simply to prevent the cable from becoming warm. The objective is to ensure that the temperature remains within the allowable range of the cable insulation and surrounding components during expected operating conditions.

3. Thermal Protection for EV Charger Power Modules

Power modules are major heat sources in high-power charging equipment.

Depending on the charger architecture, they may include:

· MOSFETs

· IGBTs

· Rectifiers

· Power diodes

· AC/DC converters

· DC/DC converters

· Power inductors

Heat may increase because of:

· High continuous power

· Cooling fan failure

· Restricted airflow

· Dust accumulation

· High ambient temperature

· Overload operation

· Heat-sink limitations

Electronic temperature monitoring can provide real-time information to the charger controller. A mechanical thermal protector can provide an additional independent hardware-level response where appropriate.

The protector should be thermally coupled to the location that best represents the temperature being protected. Simply measuring cabinet air temperature may not accurately represent the temperature of a local power-device hot spot.

4. Thermal Protection for Relays and Contactors

Relays and contactors are commonly used to control power within EV charging systems.

Their temperature may increase because of:

· Contact resistance

· Coil heating

· Switching losses

· Mechanical wear

· Contact degradation

As contact resistance increases, heat generation can also increase. Excessive heating may contribute to:

· Contact welding

· Failure to disconnect

· Increased voltage drop

· Reduced component life

· Charging system malfunction

A thermal protector installed in an appropriate location can provide an additional protection layer.

The exact mounting location is important because the protector must respond to the temperature of the component it is intended to protect rather than simply the surrounding cabinet temperature.

5. Thermal Protection for Transformers

Transformers generate heat through copper losses and core losses.

In applications where a transformer is used, excessive winding temperature can accelerate insulation aging and reduce service life.

A thermal protector may therefore be mounted close to the winding or another appropriate thermal monitoring location.

The selection should consider:

· Winding operating temperature

· Insulation system

· Ambient temperature

· Load profile

· Thermal rise

· Trip temperature

· Reset temperature

· Installation method

The actual allowable temperature should always be determined from the transformer design, insulation system, component specifications, and applicable requirements rather than from a generic temperature value.

6. Thermal Protection for Cooling Fan Motors

Cooling fans are important in many high-power EV chargers.

If a fan stops because of:

· Motor failure

· Bearing wear

· Dust accumulation

· Mechanical blockage

· Power supply problems

the temperature inside the charger may increase rapidly.

Thermal protection integrated into or installed near a fan motor can help protect the motor windings from excessive temperature.

Auto-reset protection may be appropriate for some fan applications where automatic recovery is acceptable. The correct reset behavior should be determined by the overall system safety and restart strategy.

7. Thermal Protection for PCB Hot Spots

Modern EV chargers contain compact power electronics where localized hot spots can develop around:

· Power MOSFETs

· Gate drivers

· Voltage regulators

· Power inductors

· High-current PCB traces

· Other power devices

An ambient temperature sensor may not detect a localized hot spot quickly enough.

Where appropriate, thermal protection or temperature sensing can be positioned closer to the component of concern.

The key principle is:

Protect the actual thermal hot spot, not simply the easiest location to measure.

How to Choose the Right Type of Thermal Protector

Different thermal protection technologies perform different functions. The correct choice depends on whether the system requires independent circuit interruption, continuous temperature monitoring, automatic recovery, one-time fail-safe protection, or temperature control.

Common options include:

1. Bimetal thermal protectors

2. Miniature thermal protectors

3. Thermal switches/thermostats

4. Thermal fuses

5. NTC/PTC temperature sensors

1. Bimetal Thermal Protectors

Bimetal thermal protectors use a temperature-sensitive bimetal mechanism to open or close electrical contacts when a specified temperature is reached.

Depending on the design, they may provide automatic or manual reset behavior.

Advantages

· Simple mechanical operation

· Independent hardware-level protection

· Compact construction

· Reliable switching

· Suitable for repeated operation in appropriate applications

· Suitable for volume production

Typical Applications

· Transformers

· Relays

· Contactors

· Fan motors

· Power supplies

· Industrial charging equipment

2. Miniature Thermal Protectors

Miniature thermal protectors are useful when installation space is limited.

Typical applications may include:

· EV charging guns

· Charging connectors

· Portable EV chargers

· Compact power modules

· Cable assemblies

· Small transformers

· PCB assemblies

Their compact size can simplify integration into confined spaces, but the thermal response and electrical rating must still be validated for the application.

3. Thermal Switches and Thermostats

Thermal switches or thermostats are often used for temperature control rather than independent safety shutdown.

For example, a thermostat may control a cooling fan based on cabinet temperature.

Typical functions include:

· Starting a cooling fan

· Stopping a cooling fan

· Activating ventilation

· Controlling heaters

· Maintaining enclosure temperature

This differs from an independent thermal protector whose primary purpose is to interrupt a circuit when an over-temperature condition occurs.

4. Thermal Fuses

A thermal fuse provides one-time over-temperature protection.

Once its operating temperature is reached, the internal element permanently opens the circuit and must be replaced.

Thermal fuses can be useful as a fail-safe protection layer in applications where a severe overheating event should permanently disconnect the circuit.

Typical applications may include:

· Transformers

· Battery-related equipment

· Chargers

· Power supplies

· Other safety-critical thermal protection applications

Because they cannot reset, thermal fuses are generally considered differently from reusable thermal protectors.

5. NTC/PTC Temperature Sensors

NTC and PTC thermistors are temperature-sensing devices rather than independent mechanical circuit interrupters.

They can provide continuous temperature information to the charger controller.

The control system may then:

· Reduce charging current

· Increase fan speed

· Trigger an alarm

· Pause charging

· Shut down the charger

· Record thermal data

This enables intelligent thermal management.

However, electronic temperature protection depends on the sensor, controller, firmware, communication, and power system functioning correctly. For applications requiring independent hardware protection, a mechanical thermal protector may be used as an additional layer where appropriate.

Thermal Protector vs. Thermal Fuse vs. NTC Sensor

These devices are not necessarily alternatives. A well-designed system may combine several of them.

Which Thermal Protection Solution Should You Choose?

A simplified selection approach is:

The final selection should always be validated against the actual application.

How to Select the Correct Trip Temperature

Trip temperature is one of the most important selection parameters, but it should not be selected independently.

The goal is to achieve two things simultaneously:

1. Avoid nuisance trips during normal operation.

2. Activate protection before the protected component reaches an unacceptable temperature.

Choosing the highest available temperature is therefore not necessarily the best approach.

Step 1: Determine the Maximum Allowable Temperature

Start with the component being protected.

Review the manufacturer's specifications for:

· Maximum operating temperature

· Insulation temperature rating

· Material temperature limits

· Connector temperature limits

· Semiconductor temperature limits

· Applicable product requirements

Do not assume that one generic temperature limit applies to all EV charger components.

Step 2: Measure the Actual Operating Temperature

Thermal testing should be performed under representative conditions.

Consider testing at:

· Rated charging current

· Maximum expected charging power

· Long-duration charging

· Highest expected ambient temperature

· Restricted ventilation

· Maximum enclosure temperature

· Other relevant operating conditions

Useful measurement methods may include:

· Thermocouples

· RTD sensors

· NTC sensors

· Infrared thermal imaging

· Data acquisition systems

The objective is to establish the actual thermal profile of the product.

Step 3: Consider Ambient Temperature

Ambient temperature directly affects component temperature.

Outdoor EV chargers may experience:

· High summer temperatures

· Direct solar radiation

· Enclosed cabinets

· Restricted ventilation

· Rapid seasonal temperature changes

A design that performs well at room temperature may behave differently in a high-temperature outdoor installation.

Step 4: Evaluate Temperature Rise

A useful engineering relationship is:

Operating Temperature = Ambient Temperature + Temperature Rise

For example, if a component operates at a 40°C ambient temperature and has a measured temperature rise of 55°C, its operating temperature is approximately 95°C.

This information provides a much better basis for selecting a thermal protector than ambient temperature alone.

Step 5: Consider Trip Temperature Tolerance

The nominal trip temperature is not necessarily the exact temperature at which every device will open.

The manufacturer should provide the relevant operating tolerance.

For applications with narrow thermal margins, engineers should consider the complete temperature operating window rather than relying only on the nominal trip value.

Step 6: Consider Reset Temperature

For auto-reset thermal protectors, reset temperature is also important.

If the trip and reset points are too close together, the protector may repeatedly open and close while the overheating condition remains.

Repeated thermal cycling can result in:

· Charging interruptions

· Contact wear

· Reduced service life

· Unstable operation

The trip/reset differential should therefore be evaluated against the thermal characteristics of the application.

Step 7: Consider Thermal Response

Different components heat at different rates.

A protector that responds too slowly may not provide adequate protection for a rapidly heating component.

Conversely, an excessively sensitive solution may create unnecessary interruptions.

Step 8: Validate Through Thermal Testing

Final selection should be confirmed through testing.

Depending on the application, validation may include:

· Continuous charging

· Maximum power operation

· Repeated charging cycles

· High ambient temperature

· Low ambient temperature

· Restricted ventilation

· Cooling fan failure

· Relevant overload conditions

· Actual installation configuration

· Accelerated life testing where applicable

The objective is to confirm that the protector remains inactive during normal operation while providing the intended response under abnormal thermal conditions.

Thermal Protector Selection Parameters

Before selecting a thermal protector, engineers should evaluate the complete parameter set rather than only the trip temperature.

How to Select a Thermal Protector for an EV Charging Gun

For charging gun applications, the selection process should focus on the actual connector temperature and available installation space.

1. Identify the Hot Spot

Determine whether the highest temperature occurs at:

· Connector contacts

· Terminals

· Cable termination

· Internal conductors

· Other components

2. Measure Temperature Under Maximum Current

Test at the intended charging current and maximum expected ambient conditions.

3. Determine the Allowable Temperature

Check the specifications of:

· Connector

· Housing material

· Cable insulation

· Terminals

· Other temperature-sensitive components

4. Select the Trip Temperature

The trip point should provide sufficient protection margin while avoiding nuisance operation during normal charging.

5. Confirm Electrical Rating

If the thermal protector directly interrupts the circuit, its electrical rating must be compatible with the circuit voltage, current, switching conditions, and load characteristics.

6. Confirm Mechanical Integration

Check:

· Protector dimensions

· Mounting location

· Lead-wire routing

· Insulation clearance

· Connector interference

· Vibration resistance

7. Select Reset Behavior

Determine whether the system should:

· Automatically recover after cooling

· Require a controlled restart

· Require manual inspection before restart

8. Validate the Complete Charging Gun

Final validation should be performed with the thermal protector installed in its actual location.

Auto-Reset vs. Manual-Reset Thermal Protectors

The better option depends on the system's safety philosophy and restart requirements.

Auto-Reset

An auto-reset thermal protector reconnects the circuit after temperature falls below its reset threshold.

Potential Advantages

· Automatic recovery

· Reduced maintenance

· Less downtime

· Suitable for unattended equipment

Potential applications include:

· Fan motors

· Some transformers

· Portable chargers

· Certain residential charging equipment

However, auto-reset should not be selected simply for convenience. The system must be able to safely recover after the over-temperature condition has been removed.

Manual Reset

A manual-reset protector requires intervention before operation can resume.

Potential Advantages

· Prevents automatic restart

· Encourages inspection after an overheating event

· Helps avoid repeated thermal cycling

· Suitable for applications where restart requires authorization

It may be considered for higher-risk or higher-power equipment where automatic recovery is undesirable.

Want a deeper breakdown of the technical differences? Check out our dedicated article on [Auto-Reset vs. Manual-Reset Thermal Protectors]

Common Thermal Protector Selection Mistakes

Mistake 1: Choosing the Highest Available Trip Temperature

A higher trip temperature does not automatically mean better reliability.

If the protector operates too late, the protected component may already have exceeded its allowable temperature.

Choose based on measured thermal behavior and component limits, not the highest available rating.

Mistake 2: Installing the Protector Too Far from the Heat Source

Thermal conduction takes time.

A protector installed too far from the actual hot spot may respond later than expected.

Where practical, establish good thermal coupling between the protector and the component being protected.

Mistake 3: Measuring Cabinet Air Instead of the Hot Spot

Cabinet air temperature may be significantly lower than the temperature of:

· Connector contacts

· Transformer windings

· Power devices

· High-current terminals

Protection should be based on the relevant component temperature.

Mistake 4: Using One Protector for the Entire Charger

Different components have different thermal characteristics.

A charging gun, transformer, cable, power module, and cooling fan may require different protection solutions.

Mistake 5: Ignoring High Ambient Temperature

Outdoor EV chargers can experience significantly higher temperatures than laboratory environments.

Thermal validation should reflect the intended installation environment.

Mistake 6: Ignoring Mechanical Installation

Even a correctly selected thermal protector can perform poorly if it is improperly installed.

Consider:

· Mounting pressure

· Surface contact

· Thermal interface

· Vibration

· Moisture

· Wire routing

· Electrical clearance

Mistake 7: Relying Only on Software Protection

NTC sensors and charger controllers provide valuable thermal information, but electronic protection depends on the complete control chain.

For applications where independent hardware protection is required, a mechanical thermal protector can provide an additional layer.

A Multi-Layer Thermal Protection Strategy for EV Chargers

High-power EV charging systems may benefit from multiple thermal protection layers.

A typical architecture may include:

The exact architecture should be determined by the equipment design, applicable safety requirements, and risk assessment.

The objective is not to add as many protection devices as possible. The objective is to ensure that each protection layer has a defined function and that the overall system behaves safely under foreseeable failure conditions.

EV Thermal Protector Certification and Compliance Considerations

Certification requirements depend on both the thermal protector itself and the final EV charging equipment.

When selecting a thermal protector, engineers should consider:

· Component-level approvals

· Electrical ratings

· Insulation requirements

· Environmental ratings

· Target market

· End-product certification

· Applicable EV charging equipment requirements

Potential certifications or approvals may include UL, TÜV, IEC-related requirements, or other regional requirements depending on the product and market.

The important point is that component certification should be evaluated as part of the complete end-product compliance strategy.

Do not assume that a thermal protector with a particular certification automatically makes the finished EV charger compliant.

The exact requirements should be verified against the applicable product standards and the certification plan for the target market.

EV Thermal Protector Selection Checklist

Before approving a thermal protector for production, engineers should confirm:

Is the protected component clearly identified?

Is its maximum allowable temperature known?

Has the actual operating temperature been measured?

Has maximum ambient temperature been considered?

Has temperature rise been evaluated?

Is the trip temperature appropriate?

Has trip-temperature tolerance been considered?

Is the reset temperature suitable?

Is auto-reset or manual reset appropriate?

Does the electrical rating match the application?

Is the protector installed close enough to the relevant hot spot?

Are dimensions and mounting compatible?

Are lead wires and terminals suitable?

Have environmental conditions been considered?

Are applicable certifications verified?

Has the final design been thermally validated?

What Information Should You Provide When Requesting an EV Thermal Protector?

For OEM and ODM projects, providing detailed application information allows the manufacturer to recommend a more suitable solution.

Recommended RFQ Information

If the desired trip temperature is not known, providing actual temperature measurements is often more useful than simply requesting a “100°C” or “120°C” protector.

Custom Thermal Protection Solutions for EV Charger OEMs

Every EV charging application has different thermal, electrical, mechanical, and regulatory requirements.

Saftty supports OEM and ODM customers with thermal protection solutions for applications including:

· EV charging guns

· EV charging cables

· AC chargers

· DC charging systems

· Transformers

· Relays and contactors

· Power supplies

· Cooling fan motors

· Other temperature-sensitive electrical equipment

Customization may include:

· Trip temperature

· Reset temperature

· Temperature tolerance

· Auto-reset or manual-reset configuration

· Rated voltage

· Rated current

· Lead wire length

· Lead wire type

· Terminal configuration

· Mounting structure

· Package dimensions

· Compact designs for space-constrained applications

· Other application-specific requirements

The goal is not simply to provide a thermal protector with a specified temperature rating, but to match the protection device to the customer's actual thermal and electrical conditions.

Why Choose Saftty for EV Thermal Protection?

Selecting a thermal protector for an EV charger requires understanding both the component being protected and the complete application environment.

Saftty provides thermal protection solutions for EV chargers, charging guns, transformers, relays, power supplies, motors, and other temperature-sensitive electrical systems.

For OEM and ODM projects, our engineering team can support customers with:

· Application evaluation

· Thermal protector selection

· Temperature specification review

· Mechanical integration

· Electrical parameter matching

· Custom lead-wire and terminal configurations

· Product customization

· Sample evaluation

· Application-specific recommendations

Whether you are developing a new EV charging product or modifying an existing design, providing the application parameters and measured thermal conditions can help accelerate thermal protector selection.

Conclusion

Selecting the right thermal protector for an EV charger or charging gun is an engineering decision rather than a simple temperature-rating choice.

The most important factors include the protected component, operating temperature, temperature rise, maximum ambient temperature, electrical load, thermal response, reset behavior, installation method, environmental conditions, and applicable certification requirements.

For charging guns in particular, engineers should focus on the actual connector hot spot, available installation space, charging current, thermal coupling, and restart strategy.

A reliable EV charging thermal protection system may combine several technologies, such as temperature sensors, charger control, mechanical thermal protectors, cooling systems, and thermal fuses. Each layer should have a clearly defined role.

For OEM and ODM manufacturers, the most effective selection process is to start with the actual application and measured thermal conditions, then select and validate the protection device accordingly.

Need Customized Thermal Protection for Your EV Charging Project?

Whether you are developing EV chargers, charging guns, or high-current cables, Saftty’s engineering team is here to support your thermal management design.

Request Technical Support & Free Samples

Submit your application parameters (operating current, response temperature, mounting space, etc.) to get personalized product recommendations and engineering evaluations.

Frequently Asked Questions

Does every EV charger need a thermal protector?

Not necessarily. The need for a thermal protector depends on the system architecture, power level, thermal management strategy, safety requirements, and applicable product requirements.

Some systems may rely primarily on electronic temperature monitoring, while others may incorporate mechanical thermal protection as an independent protection layer.

Can one thermal protector protect the entire EV charger?

Usually, one device should not be assumed to protect every thermal risk in the charger.

Different components may have different operating temperatures, heat-up rates, and failure modes. Multiple protection points may therefore be appropriate in complex or high-power systems.

What is the best thermal protector for an EV charging gun?

There is no universal model that is best for every charging gun.

A suitable solution should be selected based on:

· Charging current

· Connector temperature

· Maximum ambient temperature

· Available installation space

· Electrical rating

· Trip temperature

· Reset behavior

· Thermal response

· Mechanical installation

· Certification requirements

Miniature thermal protectors may be suitable for space-constrained charging gun designs, but final selection should be validated in the actual product.

Should I choose the highest trip temperature?

No.

A higher trip temperature may reduce nuisance trips but can also delay protection until after the protected component has exceeded its allowable temperature.

The trip point should be determined from measured operating conditions and the thermal limits of the protected component.

Can an NTC sensor replace a thermal protector?

Not necessarily.

An NTC sensor measures temperature and normally relies on the charger control system to take action. A thermal protector can provide an independent hardware-level response.

The two technologies may therefore complement each other rather than replace each other.

Can a thermal protector replace an NTC sensor?

Generally, no.

A thermal protector is primarily intended to provide temperature-triggered circuit protection, while an NTC can provide continuous temperature information for intelligent control and monitoring.

Should I use auto-reset or manual-reset protection?

It depends on the system's restart strategy.

Auto-reset may be suitable when automatic recovery is safe and acceptable. Manual reset may be preferable when an overheating event should trigger inspection before the equipment can restart.

How do I determine the correct trip temperature?

Start by determining:

1. Maximum allowable component temperature

2. Normal operating temperature

3. Maximum ambient temperature

4. Temperature rise

5. Thermal tolerance

6. Required safety margin

7. Reset requirements

Then validate the selected device under representative and worst-case operating conditions.

What certifications should I consider?

Certification requirements depend on the thermal protector, end product, target market, and applicable safety requirements.

Engineers should evaluate component approvals together with the overall EV charger certification strategy rather than relying on a single certification label.

What information should I send to a thermal protector manufacturer?

At minimum, provide:

· Application

· Protected component

· Voltage

· Current

· Normal operating temperature

· Maximum ambient temperature

· Desired trip temperature, if known

· Reset requirement

· Installation dimensions

· Lead-wire requirements

· Certification requirements

· Expected production quantity

If available, provide thermal test data or temperature measurements from the actual application.