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Most mechanics have already experienced electric (BEV1) or hybrid cars (HEV2, PHEV3). The handling of these types of vehicles causes uncertainty and risk for some staff, due to the high voltage system in the vehicle. In order to avoid accidents and uncertainty, it is important to prepare properly for the operation of these types of vehicles. 

To begin with, it is important to identify the characteristic hazards that may be present in these types of vehicles. The main danger is the presence of high-voltage installations with voltages higher than safe voltages, i.e. for alternating current above 25V and for direct current above 60V. These voltages are known as dangerous voltages and pose a threat to human health and life, so operating this type of installation requires proper authorization (check individual regulations in force in a given country). Dangerous voltages are typically found in the powertrain and air conditioning systems. Other systems use a classic 12V installation.


The first prerequisite for servicing a vehicle's high-voltage system is to have the necessary qualifications.  In every workshop there is usually a division of duties, i.e. there are people responsible for tyre and chassis servicing, mechanics who repair mechanical systems, and electronics technicians responsible for repairing installations and electronic systems. The competences of each of these people will be useful when servicing electric and hybrid vehicles. Many service personnel will be faced with the dilemma of defining the scope of authority that an employee should have. Legislation in many countries and vehicle manufacturers define precisely by means of regulations who, and for what activities, should have the relevant authorizations


According to these recommendations, there are four levels of qualification: 

  • untrained person
  • trained person (EiP4, FuP)
  • a person qualified to work on a high-voltage installation in a de-energised state (often called a high-voltage technician - HVT5, FHV)
  • a person qualified to work on a high voltage installation in a live state (often called a high voltage expert -HVE6)

An untrained person, from the point of view of the workshop, is any person not employed by the workshop, from the driver who arrived in a vehicle to the supplier of the parts necessary for repair. This is because It’s impossible to determine how much knowledge these people have about electrical hazards or the operation of the high voltage system. Untrained persons should be prevented from accessing the vehicle on the workshop premises and the electrical work area. Trained person is a qualification which covers workers who are not qualified as electricians (country specific), but who are trained, aware of the hazards on the vehicle, the personal protective equipment available, the markings on high voltage components and the procedures and principles of first aid. This type of training may be carried out by a person qualified to work, on a high-voltage installation, in a de-energised state.The trained person may carry out repair and maintenance work on the vehicle not related to the high voltage system, e.g. replacement of wheels, repair of systems not related to high voltage (infotainment, comfort, safety systems), but must be aware of the range of activities that can be carried out and where to report in case it becomes necessary to tamper with the high voltage system. A high voltage technician should be a person with the appropriate qualification, applicable in the country concerned, and knowledge of the construction of high voltage systems. This qualification allows you to switch off the high voltage system in the vehicle (to induce a state without voltage, in the following part will be described how to do this), disassembly and operation of devices using high voltage (after switching off the voltage), performing measurements in the hazardous area (e.g. resistance measurements). A limitation to the work of the technician is that it’s not possible to deactivate the high voltage in the vehicle, e.g. when working inside the high voltage battery (deactivation of the high voltage is not possible for technical reasons) or when the non-voltage state cannot be established due to a vehicle fault or an incorrect deactivation process. A person qualified to work on a high-voltage installation, in a live state, may interfere with the high-voltage system where, for example, it was not possible to deactivate the high voltage. Ensuring staff are suitably qualified allows risks to be minimized and work to be managed efficiently, using staff with different specialisms to operate a vehicle with a high voltage system.


1battery electric vehicle
2Hybrid Electric Vehicles
3Plug-in Hybrid Electric Vehicles
4Electrically Instructed Persons
5High Voltage Technicians
6High Voltage Experts
The high voltage system consists of high voltage consumers, i.e. the motor, the A/C compressor, the PTC heater and the high voltage source - the high voltage battery. The consumers are only powered when there is a demand for their operation, otherwise the power supply is disconnected.  This means that the high-voltage battery will not supply power to the consumers when the vehicle is stationary with the ignition switched off (e.g. in a car park). This is for safety purposes and is implemented by contactors inside the battery. They open when the ignition is switched off and prevent energy from flowing from the battery to the engine, etc. The same situation occurs, for example, during a road traffic incident, collision or when a fault is registered in the high voltage system. The contacts are opened to ensure safety. In addition to disabling the ignition, there are a number of other methods of disconnecting the high voltage. In selected vehicle models, it’s necessary to remove specific fuses or cut the marked wire loops (Fig. 1,2). These methods are intended for use by e.g. emergency services in emergency situations.
Emergency high voltage circuit breakers: loop of wires to be cut and fuses to be removed
Emergency high voltage circuit breakers: loop of wires to be cut and fuses to be removed
Emergency high voltage circuit breakers: loop of wires to be cut and fuses to be removed
The vehicle servicing and repair process, especially if interference with the high-voltage system is required, should be carried out with the voltage switched off. No repair, diagnostic or disassembly work should be carried out with the high voltage system switched on. Due to the fact that vehicles may arrive at the workshop with various faults, manufacturers have developed methods of service voltage deactivation. This method is designed to enable the high voltage to be switched off in the event of an ignition switch fault and in the event of other faults. The course of HV deactivation using the service method and a detailed discussion of when to use it will be presented in the next article in this series.

The characteristic hazards resulting from the use of high-voltage systems can be eliminated by means of appropriate protective measures, which are specified by manufacturers' recommendations and guidelines. The most commonly used basic protective equipment is gloves, dedicated to working under voltage. They are essential when carrying out the HV deactivation procedure. Once the HV has been deactivated, further operations can be carried out without gloves unless the work concerns the traction battery. Repair and dismantling of this component requires gloves even after the HV deactivation service. To be suitable for live work, gloves must be made according to the IEC 60903 standard, which regulates the levels of voltage that a glove made in a particular class protects against. The classes are defined on a scale from 00 to 4. Class 0, which protects against 1,500 volts DC and 1,000 volts AC, is most commonly used in the automotive sector. Characteristic of this type of glove is the two-triangle symbol printed on the back of the glove, which indicates that the glove is intended for energized work. Please note that the date of production should be marked on the glove or it can be written on an additional document attached to the glove. It is important to note that gloves for live work require periodic testing, e.g. every 6 months (regulations may vary from country to country).


Gloves for live work, and a close-up of the markings that should be on such gloves
Gloves for live work, and a close-up of the markings that should be on such gloves
Gloves for live work, and a close-up of the markings that should be on such gloves

Other recommended personal protective equipment includes visors for live work, insulated boots and overalls for live work. These items of equipment are used in special situations, e.g. when a vehicle comes into the workshop after an accident, fire, battery leakage or other significant fault. Visors for live work should protect against metal arcing splashes and acid (electrolyte) streams. Insulating boots shall comply with EN 50321 (regulations may vary from country to country) to protect against electric shock with a value according to the class of footwear. The classes of protection for footwear are the same as for insulating gloves, i.e. from 00 to 4. It is recommended to use footwear of at least class 0, which protects against direct voltage of 1500V and alternating voltage of 1000V. As with insulating gloves, footwear for live work is marked with two triangles. Shoes are also subject to periodical examination every 6 months. Insulated tools are an important part of personal protective equipment. Such tools must comply with the requirements of the IEC 609000 standard, which provides for testing of tools under the test voltage of 10 kV. Tools are not subject to periodical inspections. The use of insulated tools is intended to reduce the possibility of causing a short circuit between the HV system and the body. The rules for the use of tools are very similar to those for gloves. They are used during service voltage shutdown and when working on the traction battery even after HV is switched off. Always verify the condition of personal protective equipment before starting work. Mechanical damage, cuts in the protective coating or exceeding the periodic inspection date disqualify the equipment from being used. The work area should also be properly prepared for work on a vehicle with a high voltage system. The area where vehicles with high-voltage systems are operated should be secure and inaccessible to untrained people. For this purpose, a so-called "electrical work zone" should be designated. In the workshop, the workstation can be marked with contrasting tape on the floor or with posts and chains to designate the electrical work area. A sign should be put in front of the designated workstation stating that this is an electrical work area and that unauthorized persons are not allowed in. Where workplaces are separate rooms, it’s permissible to place a work zone sign on the entrance door to the workplace, in which case it’s not necessary to mark the area with tape or chain. In addition to the work area, the vehicle being worked on must also be marked. A sign indicating hazardous electrical voltages in the shape of a lightning bolt must be attached in a visible position on the vehicle in accordance with DIN 4844-2 (regulations may vary from country to country). It is also desirable to use other markings e.g. information on switching off the high voltage system or prohibition of charging the high voltage battery.


Markings on the vehicle, from left: symbol indicating that the high voltage is switched off, plate indicating dangerous voltage, prohibition of traction battery charging
Markings on the vehicle, from left: symbol indicating that the high voltage is switched off, plate indicating dangerous voltage, prohibition of traction battery charging
Markings on the vehicle, from left: symbol indicating that the high voltage is switched off, plate indicating dangerous voltage, prohibition of traction battery charging
Markings on the vehicle, from left: symbol indicating that the high voltage is switched off, plate indicating dangerous voltage, prohibition of traction battery charging

Adapting standards for the operation and servicing of cars equipped with high-voltage systems, i.e. hybrids and electric cars, may seem at first sight to be labour-intensive and expensive. Nothing could be further from the truth. Applying the basic procedures and principles presented in this article and developing certain habits will allow confident and safe servicing of vehicles with high-voltage system.