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category rating is a Roman numeral of I, II, III, or IV. This rating is also accompanied by a maximum voltage of
the circuit to be tested, which defines the voltage impulses expected and required insulation clearances. These
categories are:
Category I (CAT I): Measurement instruments whose measurement inputs are not intended to be connected to
the mains supply. The voltages in the environment are typically derived from a limited-energy transformer or a
battery.
Category II (CAT II): Measurement instruments whose measurement inputs are meant to be connected to the
mains supply at a standard wall outlet or similar sources. Example measurement environments are portable
tools and household appliances.
Category III (CAT III): Measurement instruments whose measurement inputs are meant to be connected to the
mains installation of a building. Examples are measurements inside a building's circuit breaker panel or the
wiring of permanently-installed motors.
Category IV (CAT IV): Measurement instruments whose measurement inputs are meant to be connected to the
primary power entering a building or other outdoor wiring.
Do not use this instrument in an electrical environment with a higher category rating than what is specified in
this manual for this instrument.
