Characteristics and Specifications 5 
Measurement Category
U1231A/U1232A/U1233A User’s Guide 105
Measurement Category
The Keysight U1231A/U1232A/U1233A Handheld Digital 
Multimeters have a safety rating of CAT III, 600 V.
Measurement category definition
Measurement CAT I   are for measurements performed on 
circuits not directly 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   are measurements performed on 
circuits directly connected to a low- voltage installation. 
Examples are measurements on household appliances, 
portable tools, and similar equipment.
Measurement CAT III   are measurements performed in 
building installations. 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   are measurements performed at the 
source of low- voltage installations. Examples are electricity 
meters and measurements on primary over current 
protection devices and ripple control units.