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7. Insulation resistance measurement on
PV systems
Measure the insulation resistance of PV system to verify insulation of
PV array/ string. Before starting a measurement, confirm the voltage
value which can be applied to the object under test.
Note:
● Insulation resistance of PV array may be low if it is measured in rain or
high humidity. In addition, it takes longer time to get the result due to
large static capacitances (to earth) in such weather.
● Some objects have unstable insulation resistance and may cause unstable
readings.
● Select the insulation resistance function for PV system to measure the
insulation resistance of PV array.
● The instrument may give bleep during an insulation resistance measure-
ment, however, this is not a malfunction.
● The earth measuring terminal outputs positive voltage and the line
measuring terminal negative voltage.
● Connect the earth cord to the earth (ground) terminal at measure-
ment. It is recommended to connect the positive side to the earth side
when measuring insulation resistance against ground or when a part
of the object under test is earthed. Such connection is known to be
more suitable for insulation testing since insulation resistance values
measured with the positive side connected to earth are typically less
than those taken through the reversed connection.
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