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Measurement categories (Over-voltage categories)
To ensure safe operation of measuring instruments, IEC 61010 establishes
safety standards for various electrical environments, categorized as O 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.
O
: Circuits which are not directly connected to the mains power supply.
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 overcurrent protection device (distribution
panel).
O: Device which is
not directly
connected to the
mains power supply
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