Working on HV systems

Topics:

Introduction
Body resistance
NEN 9140 (working on vehicles)
– Personnel and instructions
– Procedures
– Working on live systems
– Arc flash
NEN 3140 (working on electrical installations)
– Personnel and instructions
– High voltage (HV) and extra-low voltages (ELV)
– Working on charging equipment and outdoor conditions
– Relationship between NEN 3140 and NEN 9140
NEN 1010 (installing installations)

Introduction:
When working on electric vehicles and charging equipment, safety comes first. Electrical systems can pose hazards, such as the risk of electric shock or fire. This is especially true during maintenance, repairs and fault diagnosis. Not all hazards are immediately visible; even a system that appears to be de-energized can still contain residual energy because, for example, the capacitors have not yet been fully discharged.

To manage these risks while working on electric vehicles, NEN standards have been established in the Netherlands. These standards provide a practical implementation of the Working Conditions Decree and describe how to work safely on electrical systems. They specify which working methods must be followed and which measures are needed to limit risks.

Within automotive engineering a distinction is made between:

work on the vehicle and
work on electrical installations.

In daily practice, these areas often overlap. In the event of a fault in the charging process, for example, it is not immediately clear whether the cause lies in the vehicle, the charging equipment or the charging cable. Because different standards apply to these components, a diagnostic technician must be able to determine which standard applies in order to carry out the work safely and according to the correct procedures.

This page provides insight into the certifications required when working on e-vehicles and charging equipment. The information is by no means intended as a replacement for official documentation from vehicle manufacturers, training documentation for which certification can be obtained, or the official NEN standards and publications. Interested in NEN certification to be allowed to work on e-vehicles or charging systems? Then I can recommend the courses of FOM (Future Of Mobility)!

Body resistance:
Body resistance is the resistance the body offers against electric current. Resistance is expressed in ohms. The image alongside shows the structure of the resistances in the limbs of a human body. From basic electrical engineering we know that if we connect the plus and minus of a voltage source with a circuit containing resistors, current will flow. This is also the case in the human body when components of an electrical system are touched through which current is flowing.

At low voltages, the resistance of the skin provides sufficient insulation to prevent current from flowing through the body. That is why a mechanic can easily touch both battery terminals of a 12-volt battery at the same time (or twice 12 volts in series in a truck);
At high voltages, the skin resistance can decrease sharply due to penetration or burns. Muscle tissue and blood are good conductors. The body resistances determine how much current will flow at a given applied voltage.

The current through the body can range from noticeable to life-threatening. The human body is more sensitive to alternating current than to direct current. Below, the current levels in AC and DC are shown with their effects.

With AC, relatively low current can already cause cardiac arrhythmias. That is why AC is extra dangerous around mains frequency (50 Hz). With DC, a cardiac arrhythmia occurs less quickly than with AC, but high currents do cause severe burns and cardiac arrest. Work on high-voltage systems in electric vehicles mainly takes place on the DC section, because AC is only formed between the inverter and the electric motor in operating condition. At the moment the HV system is de-energized, components are replaced or modules in the battery pack are dismantled, work is carried out exclusively on DC (direct voltage).

Practical hazard 1:
When a technical specialist has opened a battery pack and touches the metal connectors between the modules carrying a voltage of 400 volts, the current depends on the resistances in the body. How dangerous that is also depends, among other things, on how long the contact lasts. More on that later.
To determine the current through the body, we first calculate the equivalent resistance of the series circuit:

We calculate the current flowing through the body using Ohm’s law:

This current is immediately life-threatening.

Practical hazard 2:
An electrician touches a conductor with one hand that has 230V (AC) on it. The feet provide an earth connection. We calculate the equivalent resistance (Rv1) of the legs (parallel), then the series circuit of the arm and torso (Rv2) and add these equivalent resistances together (Rv3):

We calculate the current flowing through the body using Ohm’s law:

This current can be tolerated for 0.2 seconds before it becomes life-threatening. Time therefore plays a major factor in how dangerous a current is. This is explained in the next paragraph.

Current magnitude and the duration for which the current flows are the greatest hazards. The graphs below show four coloured areas indicating the danger of current magnitude in relation to time.

Green: not externally perceptible;
Yellow: externally perceptible, muscles cramp;
Orange: muscle cramping, difficulty breathing, letting go independently is no longer possible;
Red: burns, respiratory arrest, cardiac arrest, so this area is life-threatening.

Effects of alternating current:

Below 0.5 mA, a person does not perceive anything yet;
10 mA can be tolerated for about 2 seconds before the muscles start to cramp, and at 50 mA this happens at about 100 ms;
500 mA is immediately life-threatening.

Effects of direct current:

Below 2 mA, a person does not perceive anything yet;
80 mA can be tolerated for about 100 ms before the muscles start to cramp;
500 mA is immediately life-threatening.

NEN 9140 (working on vehicles):
For electric vehicles and mobile electric machinery, the NEN 9140 standard applies. This standard applies to work on high-voltage systems in vehicles and focuses on vehicle-related components such as the HV battery, the inverter, the electric motor, the on-board charger and the air-conditioning compressor. Mechanics and diagnostic technicians who work on HV systems must be demonstrably trained and authorised through certification.
If a garage does not carry out any work on electric vehicles, they do not need additional certification.

NEN 9140:2024 applies to e-vehicles in voltage class B. This concerns systems with:

alternating voltage from 30 V AC up to and including 1000 V AC;
direct voltage from 60 V DC up to and including 1500 V DC.

The standard describes how these risks must be controlled when carrying out work on the vehicle. This includes, among other things, safely de-energizing the vehicle, checking whether the HV system is actually de-energized, and using the correct personal protective equipment. In addition, it specifies what level of knowledge and experience the technician must have in order to carry out this work independently and responsibly.

As long as the work takes place directly on the vehicle or the vehicle system, such as diagnosing the HV system, switching the vehicle to a de-energized state, or performing measurements on vehicle components, NEN 9140 applies. The image alongside shows the service plug of a Toyota, which can be used to de-energize the system.

In faults in the charging process, however, the cause is not always in the vehicle itself. The charging process consists of an interconnected whole of the vehicle, the charging equipment, and the charging cable. For a correct diagnosis, these components must be assessed together, because a defect in one of the components can affect the operation of the entire system. The charging equipment and the charging cable are not part of the vehicle and therefore fall outside the scope of NEN 9140.
These components are regarded as electrical installations, for which the NEN 3140 standard applies.
This standard applies to electrical installations and electrical tools with an AC voltage up to and including 1000 volts AC and a DC voltage up to and including 1500 volts DC.

For charging issues where measurements are carried out on the electric car, the charging cable and the wallbox, work must be performed in accordance with NEN 3140. For a diagnostic technician, it is therefore essential during fault diagnosis to determine which standard applies, because choosing the correct standard is decisive for the safe and responsible execution of the work.

Persons and designations:
The NEN 9140 standard sets requirements for persons who carry out work on or in the vicinity of electric vehicles. Anyone working with e-vehicles must have sufficient knowledge of the safety risks present, the applicable safety rules, company procedures, relevant manufacturer data, and the correct use of personal protective equipment. This knowledge is necessary to carry out work safely and responsibly.

Within NEN 9140, people are classified into different categories based on their knowledge, insight, experience, and competences. To comply with the Working Conditions Act, these persons must be designated in writing by the responsible person within the company. This concerns the:

sufficiently instructed person (VOP): may only carry out work under clear instruction and sufficient supervision.
skilled person (VP): has sufficient training and experience to independently carry out work on HV systems;
work supervisor (WV): bears responsibility for the safe organization and execution of work on electric vehicles.

The standard also mentions the “layperson”, describing that the layperson is not allowed to carry out any work on EVs.

Only persons designated in writing may carry out work on electric vehicles, and only within their authorizations. Persons without technical training, such as sales staff or receptionists, are regarded as laypersons and may not carry out any work on electric vehicles. For maintenance work, an automotive technician must at least be designated as an EV–sufficiently instructed person. Work on high-voltage components, such as repairs to an HV battery, may only be carried out by an EV–skilled person.

In the designation, a distinction is made between level of education and expertise.

The level of education determines whether someone can be considered for a particular category.
Expertise is built up through education, training, and practical experience.

An automotive technician with education level 2 therefore cannot be designated as an EV–skilled person, even with extensive experience and additional courses, but can be designated as an EV–sufficiently instructed person. An automotive technician with MBO level 3 can be designated as an EV–skilled person, provided that he or she has demonstrably been trained for work on electric vehicles, has sufficient practical experience, and has been designated in writing by the employer. A diagnostic technician at MBO level 4 also meets these conditions and, thanks to broader technical and diagnostic knowledge, is in practice the most suitable to be deployed as an EV–skilled person or to progress to EV–work supervisor.

Procedures:
Working safely on electric vehicles requires fixed and well-considered work procedures. These procedures ensure that electrical risks are controlled and that work is carried out in a predictable and safe manner. NEN 9140 describes these work procedures as a logical set of steps, always based on risk assessment, clear responsibilities, and controlled execution.

Before each task, the risks present must be identified. This involves looking at the condition of the vehicle (damage?), the nature of the work, and the environment in which the work is carried out. Based on this, it is determined which working method will be applied: working de-energized, working at a safe distance, or, in exceptional cases, working on live parts. Working de-energized is always preferred, because it removes the electrical hazard as much as possible.

When working de-energized on the HV system, a fixed sequence is always followed. This sequence is intended to prevent the risks of electric shock and unintentional energization.

The vehicle is secured against unintended movement by engaging the parking brake and removing the key or keyless transmitter. The vehicle must not be able to drive away or be activated unexpectedly;
The power source is physically separated from the HV system. This can be done by removing the service plug, which disconnects two parts of the battery pack from each other. The interlock connector can also be disconnected so that the system cannot be switched on again. To prevent someone else from activating the vehicle during the work, a padlock can be fitted;
Next, it is checked whether the HV system is actually de-energized. This is done with a suitable measuring instrument, such as a Duspol. As long as this measurement has not been carried out, the system may not be considered safe and no work may be done on the HV system.
After the work has been completed, the vehicle is put back into operation again according to a fixed procedure. This includes checking whether all safety measures have been correctly reinstalled and whether the vehicle can be used safely.

To be allowed to work on high-voltage systems, specific personal protective and safety equipment is prescribed:

Safety helmet with face shield (protection against electrical and mechanical risks);
Insulating gloves (for work on or near high-voltage parts);
Protective work clothing, such as an insulating jacket and coveralls with reflective parts;
Safety shoes or insulating overshoes (protection against electrical flashover and mechanical injury);
Insulating mat (for standing safely during work on electrical installations);
Voltage tester (for example a Duspol or comparable two-pole measuring instrument);
Insulated tools (such as pliers and screwdrivers suitable for HV work);
Barrier materials, such as cones or barrier posts (to mark the work zone);
Warning signs and pictograms (high voltage, prohibition signs);
Lockout-tagout equipment, such as locks, tags, and a lockout pouch (to secure against switching on again);
First-aid and intervention kit for electric vehicles.

Workplaces where electrical hazards may occur must be clearly marked and cordoned off. Only authorized persons may enter these zones. Non-involved persons must keep their distance at all times to prevent the risk of accidents. Tools, measuring instruments, and personal protective equipment must be suitable for working on HV systems and must be regularly checked to ensure they are in good condition.

Finally, good communication is essential. The EV work supervisor must ensure that everyone involved knows what work is being carried out, what risks are present, and which safety measures apply. If it becomes apparent during the work that the situation is unsafe or differs from expectations, the work must be stopped immediately. It may only be resumed after new measures have been determined and implemented.

In the image below, a module with cells from an EV battery pack is being dismantled. A large part of the procedure has already been followed: the vehicle has been immobilized and de-energized, the area has been cordoned off with tape and cones, and personal protective equipment has been put on.
After removing the cover, the modules have been disconnected from each other. No current can flow from module to module anymore. In this way, it has been ensured that work is carried out de-energized. The modules can then be removed. That moment is shown in the image.

In some situations, working de-energized is not possible, for example for specific measurements or functional checks. Working on live parts is then only permitted under strict conditions and may only be performed by authorized and sufficiently competent persons. Additional requirements apply regarding training, working methods, tools, and personal protective equipment. The work environment must also be arranged in such a way that the risks are reduced to a minimum.

Working on live parts:
Within NEN 9140, working on live parts on electric vehicles is only permitted in specific cases when working de-energized is technically not possible, for example for certain measurements or functional checks. Because increased risks are present, working on live parts is considered an exceptional working method that may only be applied under strict conditions.

This work may only be carried out by authorized and competent persons, such as an EV–skilled person or an EV work supervisor. A risk analysis must be carried out in advance, assessing, among other things, the nature of the voltage, the touch hazard, and the risk of arc formation. Non-designated persons may only be present under direct supervision.

Working on live parts must never become routine. Working de-energized is always preferred, and working on live parts is only permitted when it is demonstrably necessary and all safety measures have been taken. This limits the risk of electrical accidents during work on electric vehicles as much as possible.

Arc flash:
In HV systems, an arc flash can occur when a short circuit is created with tools, insulation is damaged, or when working on live parts and conductors touch each other. An arc flash is an electrical discharge through the air between two conductors with a voltage difference. Normally, air is an insulator, but when the electric field strength is high enough, the air becomes ionized. This temporarily makes the air conductive, allowing current to flow through it. This very high current creates a flash of light and a very high temperature, which can be hazardous to health.

The page Vlamboog goes into this in more detail and shows calculations with which the incident energy can be determined, so that the correct personal protective measures can be chosen.

NEN 3140 (working on electrical installations):
The NEN 3140 standard concerns the safe operation of electrical installations.
Operation is understood to mean everything that happens with an electrical installation after it has been installed and put into use. This includes, among other things, maintenance, inspections, measurements, repairs, carrying out modifications, and documenting work and checks.

For charging equipment, this means that activities such as measuring electrical parts, inspecting charging cables, replacing defective components, and testing the installation after repair fall under NEN 3140. Installations that were safe at commissioning can still become unsafe due to wear, damage, or incorrect use. NEN 3140 therefore requires that work is always carried out according to established procedures and with follow-up inspections at intervals of a maximum of five years.

The risk of touching a component that results in a dangerously high voltage, short circuit, or arc flash is high when working on electrical installations. It is therefore not permitted to carry out work on live parts on, or near, a high-voltage system, except where there is a demonstrable necessity or an assignment has been given to the VP.

Persons and designations:
Within NEN 3140, work on electrical installations may only be carried out by designated persons. The employer is responsible for this designation and records in writing which tasks and responsibilities an employee has. If no installation manager has been designated, the employer is automatically the installation manager.

The installation manager (IV) has ultimate responsibility for the safety of the electrical installation. He or she determines under what conditions work may be carried out on the installation and establishes the necessary safety measures. The work supervisor (WV) is responsible for the safe execution of specific tasks and ensures that the agreed procedures are followed. The skilled person (VP) has sufficient knowledge and experience to independently carry out work on electrical installations. Persons without designation may not carry out any work on electrical installations.

High voltage (HV) and extra-low voltage (ELV):
NEN 3140 applies to electrical installations with an AC voltage up to and including 1000 volts AC and a DC voltage up to and including 1500 volts DC. For extra-low voltage, the term extra-low voltage (ELV) is used. This concerns voltages that do not pose a danger under normal circumstances, such as 12-volt and 24-volt systems.

Although work on ELV circuits involves less risk, this work may still not be performed without restriction by just anyone. Students and minors may only carry out work on electrical installations when this fits within their level of education and under sufficient supervision. Work on high-voltage parts or on parts that are indirectly connected to higher voltages is not permitted for them.

Working on charging equipment and outdoor conditions:
When working on charging equipment, the working environment must be taken into account. When working outdoors on charging equipment, work must not be carried out during thunderstorms or in conditions where safety cannot be guaranteed. In rain or damp conditions, additional measures must be taken to limit the risk of electric shock. If this is not possible, the work must be postponed.

Tools, measuring instruments, and personal protective equipment must be suitable for the work and be in good condition. The workplace must be arranged in such a way that unauthorized persons do not have access to the danger zone.

Relationship between NEN 3140 and NEN 9140:
For charging issues where measurements are performed on the electric car, the charging cable, and the wallbox, work is being carried out on electrical installations. In these situations, NEN 3140 applies. For a diagnostic technician, it is therefore essential to determine in advance whether he is working on the vehicle itself or on the electrical installation. Choosing the correct standard determines which procedures must be followed and is therefore decisive for the safe and responsible execution of the work.

NEN 1010 (installing installations):
Before charging equipment, such as a public charging station or a wallbox at a home, is put into use, it must have been installed correctly and safely. The requirements for this are laid down in the NEN 1010 standard. This standard describes how electrical installations must be designed and installed so that they operate safely for users and the environment.

When charging equipment such as a public charging station has been installed according to NEN 1010, the electrical installation meets the national safety requirements. In addition, international standards apply to the charging equipment as an electrical product, such as IEC 61851. This standard specifically focuses on the safe charging of electric vehicles and the communication between the vehicle and the charging equipment. The distinction between NEN 1010 and NEN 3140 is essential here.

NEN 1010 focuses on the design and installation of the installation.
Once the installation has been put into use, NEN 3140 applies.
This standard describes how to work safely during use, maintenance, inspections, and carrying out modifications. A charging installation that meets all requirements at handover can, through daily use, weather influences, and mechanical loads, see components deteriorate over time. Examples include damaged connectors, worn charging cables, or loosened connections in the installation.

To continue to ensure safety, periodic inspections are necessary. During these inspections, it is assessed whether the installation can still be used safely and complies with the applicable requirements.