IEC Measurement Categories PML111O
Definitions and Examples (Clause 6.5.2)
Measurement Category I Definition: Measurement category I is for measurements performed
on circuits not directly connected to a mains supply.
Examples: 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 Definition: Measurement category II is for measurements performed
CAT II on circuits directly connected to the low voltage
installation.
Examples: Household appliances, portable tools and similar
equipment.
Measurement Category III Definition: Measurement category III is for measurements
CAT III performed in the building installation.
Examples: 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 per-
manent connection to the fixed installation.
Measurement Category IV Definition: Measurement category IV is for measurements
CAT IV performed at the source of the low-voltage installation.
Examples: Electricity meters and measurements on primary over
current protection devices and and ripple control units.
IEC Pollution Degrees
Definitions (Clause 3.5.6 )
Pollution Degree 1 No POLLUTION or only dry, non conductive POLLUTION.
NOTE The POLLUTION has no influence.
Pollution Degree 2 Only- non conductive POLLUTION. Occasionally, however, a temporary
conductivity caused by condensation must be accepted.
Pollution Degree 3 Conductive POLLUTION occurs or dry, non-conductive POLLUTION occurs
which becomes conductive due to condensation which is to be expected.
