Keysight Technologies U1273A Guide De L'utilisateur page 8

Measurement Category
The Keysight U1273A/U1273AX has a safety rating of CAT III, 1000 V and CAT IV,
600 V.
Measurement CAT I
connected to the AC mains. Examples are measurements on circuits not derived
from the AC mains and specially protected (internal) mains-derived circuits.
Measurement CAT II
to a low-voltage installation. Examples are measurements on household
appliances, portable tools, and similar equipment.
Measurement CAT III
Examples are measurements on distribution boards, circuit- breakers, wiring,
including cables, bus-bars, junction boxes, switches, socket outlets in the fixed
installation, and equipment for industrial use, and some other equipment
including stationary motors with permanent connection to the fixed installation.
Measurement CAT IV
low-voltage installation. Examples are electricity meters and measurements on
primary overcurrent protection devices and ripple control units.
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Measurements performed on circuits not directly
Measurements performed on circuits directly connected
Measurements performed in the building installation.
Measurements performed at the source of the
Keysight U1273A/U1273AX User's Guide