Measurement category
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 (None, Other) : Circuits which are not directly connected to the mains
power supply.
CAT II : 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).
DANGER
● Never make measurements on a circuit in which earth potentials of
300 V or higher (in CAT IV)/ 600 V or higher (in CAT III) exist.
● Use the metal parts for test probes appropriate for the measurement
category they are used in.
● When test probes are connected to the instrument, the lower category
either of them belongs to is applied. Confirm that they are rated for the
measurement voltage of the instrument to be used.
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