HBM QuantumX Manuel D'emploi page 127

Safety instructions
Outside the rated measurement categories
In circuits not directly connected to the supply network,
the working voltage, the level of possible transients and
the energy capacity (line impedance, overcurrent limiting
devices) must be determined before choosing suitable
measuring equipment, as the empirical values of the
measurement categories are not available to fall back on.
The values then have to be compared with the ratings of
the measuring equipment.
CAT II
Measurement category II is applicable to test and mea­
suring circuits that are directly connected to the user con­
nections (sockets) of the low-voltage grid installation. It is
expected that this part of the installation will have at least
three levels with overload protection elements between
the transformer and the measuring circuit connection
point.
CAT III
Measurement category CAT III is applicable to test and
measuring circuits that are connected to the distribution
circuit of the building low-voltage grid installation. It is
expected that this part of the installation will have at least
two levels with overload protection elements between the
transformer and the measuring circuit connection point.
MX809B 11
A3757-2.2 HBM: public