Safety Notes
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 mea-
surement categories. These are defined as follows.
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
anAC electricaloutletbya powercord(portabletools,
household appliances, etc.)
CAT III:Primary electrical circuits of heavy equipment (fixed in-
stallations) connected directly to the distribution pan-
el, and feeders from the distribution panel to outlets.
CAT IV:The circuit from the service drop to the service en-
trance, and to the power meter and primary overcur-
rent protection device (distribution panel).
Higher-numbered categories correspond to electrical environ-
ments with greater momentary energy. So a measurement de-
vice designed for CAT III environments can endure greater
momentary energy than a device designed for CAT II.
Using a measurement instrument in an environment designat-
ed with a higher-numbered category than that for which the in-
strument 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
environments.
The measurement categories comply with the Overvoltage
Categories of the IEC60664 Standards.
Measurement categories (Overvoltage categories)
