Measurement Categories
These definitions were derived from the international safety standard for insulation coordination
as it applies to measurement, control, and laboratory equipment. These measurement categories
are explained in more detail by the International Electrotechnical Commission; refer to either of
their publications: IEC 61010-1 or IEC 60664.
Measurement Category III
Distribution level. Permanently installed machines and the circuits they are hard-wired to. Some
examples include conveyor systems and the main circuit breaker panels of a building's electrical
system.
Measurement Category IV
Primary supply level. Overhead lines and other cable systems. Some examples include cables,
meters, transformers, and other exterior equipment owned by the power utility.
Electronic
12
CAT I
CAT II
Appliances,
Lighting,
Receptacles
Service
Entrance
Service
Entrance
Meter
Underground
Service
Transformer
Underground Service
CAT III
MC Panels, etc.
Outbuilding
Outbuilding
Meter
CAT IV
Exterior
Transformers,
Meters, etc.