6
IEC Measurement Category Definitions
IEC Measurement Category Definitions
Definitions and Examples (Clause 6.5.2).
Measurement Category I (CAT I)
Measurement category I is for measurements performed on circuits
not directly connected to a mains supply.
Example
Measurements in circuits not derived from a mains
supply and specially protected (internal) circuits derived from a
mains supply. In the latter case, transient stresses are variable. For
that reason, it is required that the transient withstand capability of
the equipment is made known to the user.
Measurement Category II (CAT II)
Measurement category II is for measurements performed on
circuits directly connected to the low voltage installation.
Example
Household appliances, portable tools, and similar
equipment.
Measurement Category III (CAT III)
Measurement category III is for measurements performed in the
building installation.
Example
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 like, for example, stationary motors with permanent
connections to the fixed installation.
Measurement Category IV (CAT IV)
Measurement category IV is for measurements performed at the
source of the low-voltage installation.
Example
Electricity meters and measurements on primary
over-current protection devices and ripple control units.
