Hioki 3511-50, Instruction Manual, Page: 9 / 140

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Safety Notes
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Overvoltage Categories
This product conforms to the safety requirements for CAT II measurement
products.
To ensure safe operation of measurement products, IEC 60664 establishes
safety standards for various electrical environments, categorized as CAT I to
CAT IV, and called overvoltage categories. These are defined as follows.
CAT I Secondary electrical circuits connected to an AC electrical 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 III Primary electrical circuits of heavy equipment (fixed installations)
connected directly to the distribution 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).
Higher-numbered categories correspond to electrical environments with
greater momentary energy, so a measurement product designed for CAT III
environments can endure greater momentary energy than one designed for
CAT II. Using a measurement product in an environment designated with a
higher-numbered category than that for which the product is rated could
result in a severe accident, and must be carefully avoided.