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IEC Category Rating
The IEC 61010 standard denes safety category ratings that specify the
amount of electrical energy available and the voltage impulses that may occur
on electrical conductors associated with these category ratings. The 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 denes 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.
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