16
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 I
Signal level. Electronic and telecommunication equipment, or parts thereof. Some examples
include transient-protected electronic circuits inside photocopiers and modems.
Measurement Category II
Local level. Appliances, portable equipment, and the circuits they are plugged into. Some
examples include light fixtures, televisions, and long branch circuits.
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.
