42 Planning the electrical installation
Protecting against ground faults in the DC input cable or
solar generator
The inverter has an insulation resistance measurement board which monitors the
insulation. Because of the leakage currents of inverters and characteristics of the PV
array, many ground fault monitoring devices do not work properly with them and non-PV-
specific monitoring devices are not recommended.
Insulation monitoring device
According to the IEC 62109-2 standard, the measurement is needed before the inverter
can be started. The insulation monitoring device measures insulation resistance between
the DC busbars and protective earth (PE). When the inverter operates, the insulation
resistance of the AC busbars against the protective earth is also measured indirectly. The
monitoring device reacts to all ground faults in IT systems which are galvanically
connected to each other.
If the insulation resistance between the conductors and the ground falls below the set
response values, the inverter trips or generates an alarm depending on the parameter
settings. The measured insulation resistance value can be read from the inverter
parameters.
Note: The insulation monitoring device measures the insulation resistance of the solar
generator also when the inverter does not operate. To disable the monitoring device
during inverter operation, refer to the firmware manual.
Safety information
The insulation monitoring device is constructed according to state-of-the-art and
recognized technical safety rules. Nevertheless, when the device is used, hazards may
occur to the life and limb of the user or of third parties, or there may be adverse effects on
the monitoring device or on other valuable property.
Use the monitoring device only:
• for the purpose for which it is intended.
• when it is in perfect technical condition as far as safety is concerned.
Only one insulation monitoring device may be used in each interconnected IT system.
When an insulation or voltage test is to be carried out, the device is to be isolated from the
system for the test period.The ground fault monitoring function is not a personnel safety or
fire protection feature.
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