Preface
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For measurements performed on circuits not directly connected to mains, for
example, electronics, circuits powered by batteries, and specially protected
secondary circuits. This measurement category is also known as CAT I.
●
CAT II:
For measurements performed on circuits directly connected to the low-voltage
installation by a standard socket outlet, for example, household appliances
and portable tools.
●
CAT III:
For measurements performed in the building installation, such as junction
boxes, circuit breakers, distribution boards, and equipment with permanent
connection to the fixed installation.
●
CAT IV:
For measurements performed at the source of the low-voltage installation,
such as electricity meters and primary overcurrent protection devices.
Figure 1-2: Examples of measurement categories
The higher the category, the higher the expected transient overvoltage. Overvol-
tages can overload a circuit and cause electrical and physical damage. Therefore,
use the measurement instrument only in electrical environments for which the
instrument is rated.
The measurement categories correspond to the overvoltage categories of the
IEC60664 standards. Working voltages stated in context with measurement cate-
gories are always specified as effective voltages V (RMS) against earth ground.
Measurement Categories
