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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.
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