VOLTCRAFT VC-590OLED SE Mode D'emploi page 43

CAT I Measuring category I for measurements on electrical and electronic devices not
directly connected to the supply voltage (i.e. battery-operated devices, safety
extra-low voltage, signal and control voltage, etc.).
CAT II Measurement Category II is applicable to measuring circuits of electrical and
electronic equipment that is directly supplied with the mains voltage via a power plug.
This category also covers all smaller categories (e.g. CAT I for measuring signal and
control voltages).
CAT III Measuring category III for measurements in building installations (i.e. outlets or
sub-distribution). This category includes all lower categories (i.e. CAT II for
measurements on electrical devices). Measurement operation in CAT III is permissible
only using test leads with a maximum exposed contact length of 4 mm or test leads
with protective caps.
CAT IV Measuring category IV for measurements at the source of low-voltage installations
(i.e. main distribution boards, utility entry points, etc.) and outdoors (i.e. underground
cables, open lines, etc.). This category includes all lower categories. Measurement
operation in CAT IV is permissible only using test leads with a maximum exposed
contact length of 4 mm or test leads with protective caps.
Ground potential
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