To simulate different real-world environmental conditions, the standard defines several test severity classes. The severity of a class is expressed as the charging voltage of the test generator, measured in kilovolts (kV).

Key Insight: Class 3 is the normal test severity class for protection equipment. This class represents a typical environment for devices like measuring relays and protection equipment used in power plants, substations, and industrial settings.

These classes are not arbitrary; they are designed to represent specific environmental risks:

• Class 1 & 2: Corresponds to environments where measures are taken to keep discharge voltage low. For example, rooms with floors made of antistatic material.
• Class 3: Represents environments where discharge voltage is kept below 8 kV. This is common in areas with synthetic material floors where relative humidity is greater than 50%.
• Class 4: Simulates harsher environments with a high tendency to generate static electricity. This typically involves synthetic floors and low relative humidity (e.g., greater than 10% but significantly drier than the Class 3 environment), which increases the potential for high-voltage static build-up.

Understanding the methods and severity levels, we can now define what constitutes a pass or fail.