Electrical protection classes define the safety level of an electrical device against indirect contact shocks. Classified from 0 to III according to the NF EN 61140 standard, they determine the type of insulation and the protection devices built into the equipment. Any professional working on electrical installations must master this classification to choose equipment suited to their work environment. B1 B2 BR BC electrical authorization training covers in detail the safety rules related to different equipment classes.
Key takeaways:
- Electrical protection classes (0, I, II, III) are defined by the NF EN 61140 standard and classify equipment according to its mode of protection against shocks
- Class I relies on grounding, Class II on double insulation and Class III on Safety Extra Low Voltage (SELV)
- Class 0 is prohibited in Europe for new equipment since the Low Voltage Directive came into force
What is an electrical protection class?
An electrical protection class is a standardized classification (NF EN 61140, IEC 61140) that defines how a device protects its users against the risk of electric shock. This classification is based on the principle of protection against indirect contacts: it specifies the means employed to prevent a fault current from flowing through the human body in case of primary insulation failure.
The International Electrotechnical Commission (IEC) has defined four protection levels, numbered from 0 to III. Each class corresponds to a distinct safety mechanism. Equipment choice depends directly on the installation environment: a bathroom does not accept the same equipment as an industrial workshop. This concept is fundamental for any professional who selects or installs electrical equipment, as detailed in the PPE guide for electrical authorization.
Protection class and IP rating: do not confuse
The electrical protection class is often confused with the IP (Ingress Protection) rating. These are two distinct concepts. The IP rating, codified by the IEC 60529 standard, evaluates the degree of protection of an equipment enclosure against solid objects (first digit) and against water (second digit). For example, an IP44 rating means the device is protected against solid objects larger than 1 mm and against water splashes. The protection class, on the other hand, exclusively concerns electrical safety against indirect contacts and dangerous voltages. Both systems are complementary for ensuring installation safety.
The four protection classes in detail
Class 0: basic insulation without additional protection
A Class 0 device has only basic insulation between live parts and accessible parts. It has neither a protective conductor nor an earth connection. In case of insulation failure, no device limits the risk of electrocution.
This class is prohibited in Europe for new equipment under the current European standard. It can still be found on old or imported equipment, particularly old electric heaters. If you identify a Class 0 device on a worksite, it must be taken out of service.
Class I: protection by grounding
Class I is the most widespread in industry and construction. The device has basic insulation and a protective conductor connected to earth via the plug. In case of insulation failure, the fault current flows to earth and triggers the residual current device.
For a Class I device to operate safely, the installation must have a compliant earth connection and a calibrated residual current device (30 mA in domestic settings). Without an earth connection, the protection is non-existent. Voltage domains directly influence the dimensioning of this protection.
Examples of Class I devices: machine tools, industrial ovens, water heaters, washing machines, electrical panels and certain metal luminaires.
Class II: double insulation
A Class II device relies on reinforced insulation or double insulation. It requires no earth connection. The insulating enclosure replaces the additional protection provided by earthing in Class I. This type of equipment is identifiable by the concentric double square symbol engraved on its rating plate.
Class II is particularly suited to environments where the earth connection is absent or unreliable. In practice, most modern portable power tools (drills, grinders, vacuum cleaners) are designed as Class II. The same applies to wall-mounted electric radiators and many recessed luminaires.
Important note: a Class II device must never be connected to earth. Adding an earth connection to double-insulated equipment creates a fault current path not foreseen by the manufacturer. This point is covered in the electrical authorization glossary published on our website.
Class III: Safety Extra Low Voltage (SELV)
Class III concerns equipment operating on Safety Extra Low Voltage (SELV), i.e. a maximum of 50V AC and 120V DC. At these voltage levels, the risk of electric shock is considered negligible for a human being under normal conditions.
The power supply must come from a safety transformer compliant with the NF EN 61558 standard. Class III devices are found in swimming pool lighting, electric toys, doorbells and certain medical devices. In a bathroom, only SELV equipment is authorized in volume 0 (immersed zone) according to the NF C 15-100 standard. For a better understanding of electrical environment zones, consult our guide on regulatory distances and zones.
Comparison table of protection classes
| Criterion | Class 0 | Class I | Class II | Class III |
|---|---|---|---|---|
| Insulation type | Basic | Basic + earth | Double or reinforced | SELV (≤ 50V AC) |
| Earth connection | No | Yes (mandatory) | No (prohibited) | No |
| Symbol | None | ⏚ (earth) | ◻◻ (double square) | ◇III (diamond) |
| Common example | Old radiator | Industrial oven | Portable drill | Pool lighting |
| Status in Europe | Prohibited (new) | Authorized | Authorized | Authorized |
Identifying the class of an electrical device
The class symbol appears on the device’s rating plate, on its packaging or in its technical documentation. The absence of a symbol on old equipment may indicate Class 0. A device without clear marking should be treated as potentially dangerous.
In the field, the presence or absence of an earth pin on the power plug provides a first clue. A Class I device has a plug with an earth pin. A Class II device has a plug without an earth pin (two poles only). For Class III equipment, the connector is specific and incompatible with standard sockets to prevent connection to the mains. Before working on any equipment, the Voltage Absence Test (VAT) remains a mandatory preliminary step.
Protection classes and electrical authorization
Knowledge of equipment classes is an integral part of the competency framework for electrical authorization (NF C18-510 standard). An authorized B1 or B2 operator must be able to identify the class of equipment before any intervention, as prevention measures differ.
On a Class I device, the operator checks the continuity of the protective conductor and the proper functioning of the residual current device before energizing. On Class II equipment, this check is irrelevant: safety relies entirely on the integrity of the reinforced insulation. A crack in the insulating enclosure of a Class II device constitutes an immediate danger, unlike a cosmetic defect on an earthed metal casing.
In high-risk environments (wet worksite, confined space), systematic use of Class II or Class III equipment significantly reduces the risk of electrocution. This requirement is detailed in the INRS prevention procedures (ED 6127). H1 H2 HC authorization training specifically addresses High Voltage constraints where these classifications become even more critical.
Essentials for choosing the right equipment
Choosing appropriate electrical equipment depends on three factors: the usage environment (dry, wet, immersed), the quality of the available earth connection and the electrical protection levels required by the applicable standard. The insulation resistance of the equipment must match the site constraints. In case of doubt about the class of equipment or its compatibility with the installation, refer to the manufacturer’s documentation and the NF C 15-100 standard requirements to ensure personnel safety and effective protection against electric shocks.
FAQ
A Class I device uses basic insulation supplemented by an earth connection: in case of a fault, the leakage current flows to earth and triggers the residual current device. It is a protection against dangerous voltages that depends on the installation. A Class II device relies on double insulation or reinforced insulation without any earth connection. Class II provides intrinsic protection, independent of the quality of the electrical installation.
No. A Class II device must not be connected to earth. Its double insulation provides protection against indirect contacts without a protective conductor. Plugging a Class II device into a socket with earth does not pose a safety problem (the pin remains inactive), but it is prohibited to modify the device to add an earth connection.
SELV designates a voltage equal to or less than 50V AC (120V DC) delivered by a safety transformer compliant with the NF EN 61558 standard. This voltage level is considered non-hazardous to the human body under normal conditions. Devices powered by SELV correspond to Class III. To learn more about voltage domains, consult our article on electrical authorization symbols.
No. Class 0 is prohibited in Europe for all new equipment placed on the market. The Low Voltage Directive (2014/35/EU) requires at minimum Class I protection. Old Class 0 equipment may still be in service, but it must be replaced during any renovation or compliance upgrade of the installation.
Any intervention on Class I electrical equipment connected to the Low Voltage network requires at minimum B1 authorization (performing electrician) or BS (elementary intervention) according to the NF C18-510 standard. The authorization level depends on the nature of the operation: like-for-like replacement (BS) or more complex work (B1, B2, BR).
