High-Voltage Safety & Electrical Inspections of Electric Vehicles

Frequently Asked Questions About Electrical Safety in High-Voltage Vehicles

Electrical testing of high-voltage systems requires appropriate measuring instruments, clearly defined test procedures, and the necessary technical qualifications. The following questions explain key terms such as insulation resistance, equipotential bonding, and voltage-free conditions, as well as the significance of DGUV 209-093, UN ECE R100, and ISO 6469-3.

• What is a high-voltage system in a vehicle?

  In automotive engineering, high-voltage systems refer to electrical systems whose voltages exceed the range typical for conventional vehicle electrical systems.

  In electric and hybrid vehicles, depending on the vehicle, these include, for example:

  • High-voltage battery
  • HV cables
  • Electric motor
  • Inverter
  • DC/DC converter
  • On-board charger
  • Electric air conditioning compressors
  • Electric heating elements

  Due to the potential electrical hazards, special requirements apply to work on these systems.

• What does electrical safety mean in the context of an electric vehicle?

  Electrical safety encompasses measures and tests designed to prevent people from being endangered by hazardous electrical voltages or currents.

  Depending on the vehicle and the task at hand, these may include, for example:

  • De-energizing the high-voltage system
  • Verifying the absence of voltage
  • Insulation testing
  • Equipotential bonding testing
  • Visual inspection
  • Testing of electrical connections

  The specific tests required are determined by the relevant work and vehicle manufacturer specifications.

• Do electrical safety inspections have to be performed before and after every maintenance service on an electric car?

  No, such a blanket statement would not be correct.

  The safety measures and inspections required depend, among other things, on:

  • the type of work
  • the system in question
  • the condition of the high-voltage system
  • the risk assessment
  • vehicle manufacturer specifications
  • the qualifications of the person performing the work

  Therefore, not every maintenance task on an electric vehicle automatically requires a complete high-voltage safety inspection.

• What is an insulation test on an electric vehicle?

  An insulation test checks how well the electrically active components of the high-voltage system are insulated from the vehicle ground or other accessible conductive parts.
  
  A sufficiently high insulation resistance is a key component of the electrical safety of a high-voltage system.
  
  The measurement method, test voltage, and threshold value depend on the specific application and test specifications.

• What is insulation resistance?

  Insulation resistance describes the electrical resistance of insulation between electrically active parts and another reference potential, such as the vehicle body.
  
  Low insulation resistance—or insulation resistance that is below the specified limit—may indicate an insulation fault.

• Why can the insulation resistance of a high-voltage system deteriorate?

  Possible causes may include, for example:

  • damaged cable insulation
  • moisture
  • contamination
  • damaged connectors
  • defects in high-voltage components
  • mechanical damage
  • faults following repairs or accidents

  If an anomaly is detected, the cause must be systematically narrowed down in accordance with the manufacturer’s specifications.

• Is there a general threshold value for the insulation resistance of every electric vehicle?

  No.
  
  When performing workshop diagnostics, a universal threshold value should not be applied to every vehicle and every component.
  
  The required minimum insulation resistance depends on the system, the measurement method, and the underlying specification or manufacturer's guidelines.

• What insulation test voltages does the MI 3132 EV tester offer?

  The MI 3132 EV Tester enables insulation measurements with test voltages ranging from 50 V to 1,500 V DC.

  The resistance measurement range extends up to 3 GΩ.

  However, the actual test voltage to be set depends on the specific test task and the vehicle manufacturer’s specifications.

• Is it safe to measure 1,000 or 1,500 V on any high-voltage component?

  No.
  
  The maximum test voltage of a measuring instrument is not a recommendation to use that voltage for every measurement.
  
  An inappropriately high test voltage can stress or damage electronic components or the circuit in question.
  
  The specified test voltage must therefore be taken from the relevant test or manufacturer’s specifications.

• What is equipotential bonding in an electric vehicle?

  Electrical equipotential bonding electrically connects accessible conductive vehicle parts or the housings of high-voltage components to one another and to the designated vehicle potential.
  
  This is intended to prevent dangerous potential differences from arising between accessible conductive parts.

• Why is the equipotential bonding tested at low impedance?

  A reliable equipotential bonding connection should have as low an electrical resistance as possible.
  
  A low-resistance or microohm measurement can be used to verify whether the electrical connection in question has sufficiently low resistance.
  
  The permissible limit is based on the respective manufacturer’s specifications or test specifications.

• What is a microohm measurement?

  A microohm measurement is used to precisely measure very small electrical resistances.
  
  It is suitable, for example, for evaluating low-resistance equipotential bonding and bonding connections.
  
  The MI 3132 EV Tester enables four-wire microohm measurements with a test current of up to 2 A.

• Why is a four-wire measurement used for very small resistances?

  When resistance values are very low, even the resistance of the test leads and contact points can significantly affect the measurement result.
  
  In a four-wire or Kelvin measurement, current and voltage measurements are performed separately.
  
  This significantly reduces the influence of the test leads on the resistance measurement.

• What is the difference between an insulation test and an equipotential bonding test?

  These two measurements test opposing electrical properties.

  Insulation measurement:
  The highest possible electrical resistance is expected between areas that are insulated from one another.

  Equipotential bonding measurement:
  The lowest possible electrical resistance is expected between conductive parts designated for this purpose.

  Both tests can therefore be part of an electrical safety assessment.

• What does “voltage-free” mean in the context of a high-voltage vehicle?

  “Voltage-free” means that no dangerous voltage is present on the electrical components relevant to the work.
  
  Until it has been verified that the system is voltage-free in accordance with the prescribed procedure, the high-voltage system in question must always be considered to be live.

• How is it determined whether a high-voltage system is de-energized?

  Verification that the system is de-energized must be performed in accordance with the vehicle manufacturer’s and safety specifications.
  
  Appropriate voltage testers or testing equipment specified by the vehicle manufacturer must be used for this purpose.
  
  The proper functioning of the voltage tester must be verified immediately before and after verifying that the system is de-energized.

• Can the absence of voltage be detected using a standard multimeter?

  Not across the board.

  For the safety-critical verification of the absence of voltage, specific requirements apply to the testing equipment used.

  A standard multimeter should not automatically be considered equivalent to a suitable two-pole voltage tester.

  The requirements of the relevant safety standards as well as the vehicle manufacturer’s specifications must be taken into account.

• Can the MI 3132 EV Tester measure voltages?

  Yes.

  The MI 3132 EV tester offers, among other features:

  • DC voltage measurement
  • TRMS voltage measurement
  • Frequency measurement

  However, these measurement functions must be distinguished from the formal safety-related verification of the absence of voltage in accordance with the prescribed work procedure.

• What is the MI 3132 EV Tester?

  The Metrel MI 3132 EV Tester is a measuring instrument specifically designed for electrical safety tests on electric vehicles.

  Its functions include, among others:

  • Insulation resistance measurement
  • Microohm measurement
  • Low-resistance measurement
  • DC voltage measurement
  • TRMS voltage and frequency measurement
  • Visual safety and functional tests
  • Programmable test sequences

  The device is therefore suitable for various electrical testing tasks on high-voltage vehicles and high-voltage components.

• Can the MI 3132 save and document test results?

  Yes.

  Measurements can be managed within the device and then analyzed using the Metrel software.

  The Metrel ES Manager supports, among other things:

  • Preparation of test setups
  • Downloading of measurement results
  • Tabular and graphical display
  • Storage
  • Printing and report generation

  This enables the implementation of standardized test procedures and traceable documentation.

• What does “CAT III 1000 V” mean for the MI 3132?

  CAT III 1000 V refers to the specified overvoltage category and the corresponding maximum voltage of the measuring instrument.

  The MI 3132 EV Tester is rated CAT III 1000 V.

  The measurement category is an important safety feature; however, it does not replace the need to verify whether the device, test leads, and measurement procedures are suitable for the specific vehicle measurement.

• Does CAT III 1000 V automatically mean it is approved for any measurement on an electric car?

  No.

  The measurement category alone is not sufficient to support such a blanket statement.

  In addition, the following factors, for example, must be taken into account:

  • specific measurement task
  • maximum system voltage
  • measurement method
  • test leads
  • connectors
  • vehicle manufacturer specifications
  • user qualification
• What is the function of the MTi 801 in high-voltage measurements?

  The MTi 801 is a professional digital multimeter featuring:

  • CAT III 1,000 V
  • CAT IV 600 V
  • Voltage measurement up to 1,000 V
  • Resistance measurement
  • Continuity test
  • Insulation testing with test voltages of 100, 250, 500, and 1,000 V

  It can be used for suitable electrical measurement tasks.

  For specialized high-voltage safety tests with automated procedures, microohm measurements, and comprehensive documentation, the MI 3132 EV Tester offers a significantly broader range of functions.

• Can a current clamp be used for high-voltage diagnostics?

  A suitable current clamp allows for contactless current measurement on a single conductor, provided that the measurement range, current type, insulation, and application are compatible with the specific measuring device.
  
  Leitenberger, for example, offers the STZ 01 and STZ 02 current clamp adapters for different current ranges.
  
  However, current measurement with a current clamp does not replace electrical safety or insulation testing.

• What does UN ECE R100 regulate?

  UN Regulation No. 100 sets forth requirements for the approval of vehicles with regard to electric propulsion systems and rechargeable electric energy storage systems (REESS).
  
  Among other things, it addresses electrical safety, equipotential bonding, and insulation resistance.
  
  However, UN ECE R100 is not a general step-by-step workshop manual for every maintenance or repair task.

• Is UN ECE R100 a workshop testing regulation?

  This is not intended as a general repair or maintenance manual.
  
  UN ECE R100 is primarily a regulation for vehicle and component type approval.
  
  Some of the measurement methods described therein may be relevant for specific test equipment and testing tasks.
  
  However, the specific measurements a repair shop must perform following a particular repair depend primarily on the vehicle manufacturer’s specifications, the scope of work, and occupational safety requirements.

• What does ISO 6469-3 cover?

  ISO 6469-3 specifies requirements for the electrical safety of electrically powered road vehicles with Class B voltage circuits.
  
  In particular, it addresses the protection of persons against electric shock and thermal hazards.
  
  However, the standard expressly does not constitute a complete set of safety instructions for maintenance and repair personnel.

• Which version of ISO 6469-3 is currently in effect?

  The current version is ISO 6469-3:2021, Edition 4.

  This edition was reconfirmed in 2026.

  A fifth edition is currently in the standardization process and is available as a Committee Draft.

  When referring to standards, you should therefore regularly check which edition is currently valid.

• What is DGUV Information 209-093?

  DGUV Information 209-093 describes how to organize safe work on vehicles with high-voltage systems based on a risk assessment.
  
  It also contains minimum requirements for the qualification of personnel working on such vehicles.
  
  The document applies to service shops as well as development and manufacturing.

• What does FUP or FuP mean?

  FuP stands for Qualified Person.

  In the DGUV 209-093 qualification model, this corresponds to Level 1S for mass-produced vehicles.

  A FuP may perform certain tasks on vehicles with high-voltage systems that do not directly involve the high-voltage system or that have been approved in accordance with the established work procedures.

• What does FHV stand for?

  FHV stands for High-Voltage Specialist.

  In the field of production vehicles, this corresponds to qualification level 2S.

  A person with this qualification may perform work on the high-voltage system, provided it has been de-energized, in accordance with their scope of responsibilities and qualifications.

• What does Level 3S mean?

  According to DGUV 209-093, Level 3S denotes the qualification required for work on live high-voltage systems.

  This type of work places higher demands on qualifications, work organization, safety measures, and personal protective equipment.

• What qualifications are required to perform an insulation test?

  This cannot be determined in general terms based solely on the name of the test.

  Key factors include:

  • Condition of the high-voltage system
  • Test procedure
  • Work step
  • Vehicle manufacturer’s specifications
  • Risk assessment

  The required qualification level must therefore be determined for the specific task.

• Is purchasing a high-voltage tester sufficient to be authorized to work on high-voltage vehicles?

  No.
  
  A suitable measuring device is no substitute for professional qualifications.
  
  Work on high-voltage systems requires not only that the necessary organizational and technical requirements be met, but also that suitable testing equipment, tools, and, if necessary, personal protective equipment be available.

• Are special test leads required for high-voltage measurements?

  Yes, the test leads and accessories used must be suitable for the respective voltage, measurement category, and measurement task.
  
  Not only the measuring instrument itself, but the entire measurement chain must be suitable for the intended application.
  
  Damaged or unsuitable test equipment must not be used.

• Does an insulation test replace the leak test for a high-voltage battery?

  No.

  The insulation test evaluates an electrical property of the high-voltage system.

  The leak test, on the other hand, evaluates the mechanical or fluid tightness of the battery housing or a component.

  You can find suitable devices under Leak testers for HV batteries and high-voltage components.

• Does an electrical safety inspection provide any information about the battery's state of health?

  No.

  Electrical safety tests and state-of-health assessments serve different purposes.

  The state of health describes the aging or condition of the high-voltage battery.

  Specialized test equipment for HV battery diagnostics and state-of-health (SoH) testing is available for this purpose.

• Is the high-voltage electrical safety inspection related to a wallbox inspection?

  These are different types of testing.

  During a high-voltage safety test, the vehicle—or more specifically, its high-voltage system—is inspected.

  In contrast, during a wallbox or EVSE test, the electrical charging device is tested, and the vehicle’s condition is simulated using a suitable EVSE adapter.

  You’ll be able to find suitable devices in the future under Wallbox, EVSE, and Charging Cable Testers.

• Can Mode 3 charging cables be tested with the MI 3132?

  The MI 3132 supports the corresponding electrical measurement functions. For convenient and standardized testing of Mode 3 charging cables, a dedicated charging cable adapter is also used.

  When used with compatible testers, the Metrel A 1832 enables electrical safety and functional tests on Type 2 Mode 3 charging cables.

  You can find these products under Wallbox, EVSE, and Charging Cable Testers.

• Can the MI 3132 still be used after an accident?

  The MI 3132 is generally designed for various electrical safety tests on electric vehicles and is also specified by the manufacturer for safety tests following accidents, among other applications.
  
  However, the decision regarding which measurements may be performed or are required on a specific vehicle involved in an accident must be based on the vehicle’s condition, manufacturer specifications, a risk assessment, and the technician’s qualifications.

• Why is it important to document high-voltage electrical tests?

  Traceable documentation can record:

  • which vehicle or component was tested,
  • which measurement was performed,
  • which test parameters were used,
  • which results were obtained,
  • and when the test took place.

  Automated test equipment and appropriate software support reproducible test procedures and traceable quality assurance.