There are four IEC 61010 category levels defined, from I to IV.

• A. There are three IEC 61010 category levels defined, from I to IV
• B. There are four IEC 61010 category levels defined, from I to IV
• C. There are five IEC 61010 category levels defined, from I to IV
• D. There are unlimited levels defined

Answer: (B)

Four category levels are defined, labeled I through IV, to reflect different environments where equipment might operate and the corresponding insulation stresses it could face. This structure guides how safety tests and insulation requirements are applied. The levels increase with the potential energy and transient voltages the equipment could encounter: Category I covers devices not connected to mains, Category II covers typical mains-powered appliances plugged into outlets, Category III covers fixed installations and distribution wiring, and Category IV covers the origin of the supply at the service entrance. Because of this explicit four-level framework, the statement describing four levels is correct, while the others misstate the number of categories.