10 Troubleshooting
SMA Solar Technology AG
54
SB13_21TL-IA-en-65
Installation Manual
10.5 Red LED Permanently On
If the red LED is permanently on during operation, there is an earth fault present in the PV array or at
least one of the varistors for overvoltage protection is defective.
Procedure:
• Check the PV array for earth faults (see Section 10.5.1 "Checking the PV Array for Earth Faults",
• If the red LED does not go out, check the function of the varistors (see Section 10.5.2 "Checking
the Function of the Varistors", page 55).
10.5.1 Checking the PV Array for Earth Faults
If the red LED is on and the inverter displays the message
Riso
, there is an earth fault in the PV array.
The electrical insulation between the PV plant and earth is defective or insufficient.
Proceed as follows to check each string in the PV plant for earth faults.
1. Disconnect the inverter from all voltage sources (see Section 8).
2. Measure the voltages:
• Measure the voltages between the positive pole and the earth potential (PE).
• Measure the voltages between the negative pole and the earth potential (PE).
• Measure the voltages between the positive and negative poles.
If the following results are returned simultaneously, there is an earth fault in the PV plant.
☑ All measured voltages are stable.
☑ The sum of the two voltages against earth potential is approximately equal to the voltage
between the positive and negative poles.
• Determine the location of the earth fault via the ratio of the two measured voltages, and
eliminate the earth fault.
If there is no earth fault present and the message is still displayed, contact the SMA Service Line.
Danger to life due to electric shock
In the event of an earth fault, high voltages can be present.
• Only touch the cables of the PV array by their insulation.
• Do not touch any parts of the sub-structure or frame of the PV array.
• Do not connect PV strings with earth faults to the inverter.
