7.1 Information
Measurement Category I:
Measurement category I is valid for electrical equipment
used in instruments in which only low excessive voltage
are likely to occur, such as e.g. within instruments after the
input transformer.
Measurement Category II:
Measurement category II is valid for electrical equipment
where no lightning voltages must be considered but where
excessive voltages might be generated by control equip-
ment, e.g. switch gear. Electrical equipment belonging to
this category, for example, domestic appliances which do
not have a transformer between internal circuitry and
mains
Measurement Category III:
In addition to category II, category III contains electrical
equipment with special requirements regarding safety and
availability. Example: domestic installations, protective de-
vices, sockets, switches, etc.
Measurement Category IV:
Electrical equipment for which lightning effects must be
considered belongs to category IV. This includes e.g. con-
nection to overhead power lines, earth cable to water
pumps, etc.
In previous editions of the DIN VDE 0411-1:1994, the
term overvoltage class has been used in lieu of mea-
surement circuit class.
Pollution Degree
The insulation property of test and measuring instruments
can be strongly impaired by surface contamination. Dust
and soot particles or water from conductive connections
which can considerable reduce the surface resistance of
the insulating parts.
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Information
