Hioki 3805-50, Instruction Manual, Page: 85 / 156

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This instrument complies with CAT II (1000 V) and CAT III (600
V) safety requirements.
To ensure safe operation of measurement instruments IEC
61010 establishes safety standards for various electrical envi-
ronments, categorized as CAT I to CAT IV, and called measure-
ment categories. These are defined as follows.
Higher-numbered categories correspond to electrical environ-
ments with greater momentary energy. So a measurement
device designed for CAT III environments can endure greater
momentary energy than a device designed for CAT II.
Using a measurement instrument in an environment designated
with a higher-numbered category than that for which the instru-
ment is rated could result in a severe accident, and must be
carefully avoided.
Never use a CAT I measuring instrument in CAT II, III, or IV envi-
ronments.
The measurement categories comply with the Overvoltage Cate-
gories of the IEC60664 Standards.
Measurement categories (Overvoltage categories)
CAT I: Secondary electrical circuits connected to an AC elec-
trical outlet through a transformer or similar device.
CAT II: Primary electrical circuits in equipment connected
to an AC electrical outlet by a power cord (portable
tools, household appliances, etc.) CAT II covers
directly measuring electrical outlet receptacles.
CAT III: Primary electrical circuits of heavy equipment
(fixed installations) connected directly to the distri-
bution panel, and feeders from the distribution
panel to outlets.
CAT IV: The circuit from the service drop to the service
entrance, and to the power meter and primary
overcurrent protection device (distribution panel).