Technical Articles

What are the ratings per IEC/EN 60664-1?

IEC/EN 60664-1 is an international standard that deals with insulation coordination for electrical equipment in low-voltage systems. It provides guidelines and requirements for determining the appropriate levels of insulation and clearances needed to ensure electrical safety. One important aspect covered by this standard is the ratings assigned to different types of electrical installations, which play a crucial role in maintaining safe operating conditions and preventing electrical breakdowns.

Main Ratings Categories:

When it comes to insulation coordination, IEC/EN 60664-1 defines several important ratings that need to be considered. These ratings help determine the proper level of protection against electrical hazards in a given installation. Here are three main categories of ratings specified by the standard:

Rated Insulation Voltage (Ui):

The Rated Insulation Voltage, denoted as Ui, is the maximum voltage level for which the insulation system of a specific electrical equipment is designed. It represents the highest voltage that can be applied to the equipment under normal operating conditions without causing insulation failure. The objective of Ui is to ensure that the equipment remains operational and safe for use within its expected voltage ranges.

Rated Impulse Withstand Voltage (Uimp):

Rated Impulse Withstand Voltage, denoted as Uimp, is another important rating defined by IEC/EN 60664-1. It represents the ability of an equipment's insulation to withstand transient overvoltage caused by lightning strikes, switching surges, or other sudden voltage spikes. Uimp is typically higher than Ui and ensures that the equipment can handle these temporary voltage surges without suffering from insulation breakdown.

Climatic Category:

The climatic category is a rating that takes into account the environmental conditions in which electrical equipment is expected to operate. It defines the range of ambient temperature and humidity within which the equipment can safely perform without any adverse effects on its insulation. The climatic category is crucial for determining the suitability of equipment for different operating environments, such as tropical climates with high temperatures and humidity levels, or arctic climates with extreme cold.


IEC/EN 60664-1 plays an important role in ensuring electrical safety by providing guidelines for insulation coordination. The ratings defined by this standard, such as Rated Insulation Voltage (Ui), Rated Impulse Withstand Voltage (Uimp), and Climatic Category, help engineers and designers select appropriate electrical equipment and maintain safe operating conditions. Adhering to these ratings ensures that installations are adequately insulated, reducing the risk of electrical breakdowns and ensuring the safety of both individuals and property.



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