KYORITSU 5020 Instruction Manual - Manual (Page 6)

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Safety symbols
Refer to the instructions in the manual.
Indicates a Instrument with double or reinforced insulation
Indicates that this instrument can clamp on live bare conductors
when the voltage to be tested is below Circuit – Ground-to-Earth
voltage against the indicated Measurement Category.
∼ Indicates AC
Indicates DC
Measurement categories(Over-voltage categories)
To ensure safe operation of measuring instruments, IEC 61010 establishes
safety standards for various electrical environments, categorized as
CAT.I to CAT.IV, and called measurement categories. Higher-numbered
categories correspond to electrical environments with greater momentary
energy, so a measuring instrument designed for CAT.III environments can
endure greater momentary energy than one designed for CAT.II.
CAT.I : Secondary electrical circuits connected to an AC electrical
outlet through a transformer or similar device.
CAT.II : Primary electrical circuits of equipment connected to an AC
electrical outlet by a power cord.
CAT.III : Primary electrical circuits of the equipment 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 over-current protection device
(distribution panel).