The Difference Between Class 2 and Class II

What is Class 2?

Class 2 is a power supply safety classification defined by Underwriters Laboratories (UL); the official standard is UL 1310 — Standard for Safety for Class 2 Power Units. This standard is derived from the National Electrical Code (NEC, NFPA 70), and its core design principle is to limit the output energy of the power supply to below a safe threshold, ensuring that even in the event of a malfunction, it will not be sufficient to cause a fire or a severe electric shock.

What is Class II?

The definition of Class II (note: Roman numeral II) is derived from the international standard IEC 61140 (EN 61140), which classifies electrical equipment into four protection levels—Class 0, Class I, Class II, and Class III—based on the method of protection against electric shock. Specifically:

Class I: Relying on basic insulation + protective earthing to prevent electric shock (typical three-pronged equipment with a ground wire)

Class II: Relying on double insulation or reinforced insulation to prevent electric shock, without relying on grounding (typically two-prong devices without a ground wire)

Class III: Powered by SELV (Safety Extra-Low Voltage), requiring no additional insulation protection