A 1472, A1579 Leakage current clamp
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4.3.2 Insulation resistance testing
The standard high voltage insulation resistance test can sometimes not be
carried out
– if the installation is not allowed to be disconnect for a longer
time or sensitive equipment is connected.
In this case the leakage current measurement can conditionally be used as
an alternative to the insulation resistance test.
However the results cannot be directly compared because the leakage
currents are flowing through resistance and capacitances between line and
earth. Degradation of isolation causes only a drop of the resistance and not
of the capacitance.
The applicability of leakage current measurement as an alternative to the
insulation resistance test depends on following factors:
The ratio between capacitive and resistive leakage currents in the
installation should be known. If the resistive part is completely
blinded by the capacitive leakage currents, the measurement will
give no indication about the insulation. If both portions are
comparable and the number of loads connected to the mains is not
changing in time at least trends can be determined.
Old measuring results should be available. This will enable
observing the trends.
The capacitive and resistive currents are not simply summed
therefore the interpretation of results should be made by a skilled
person.
Note:
Before using this alternative test check if it is allowed in your country.
