4
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
: 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 over-current protection device (distribution
panel).