Checking the PV System for Ground Faults
Qualified person
If the red LED is glowing and the event number 3501, 3601 or 3701 is being displayed in the Results menu on the inverter user interface, there may be a ground fault present. The electrical insulation from the PV system to ground is defective or insufficient.
DANGER
Danger to life due to electric shock when touching live system components in case of a ground fault
If a ground fault occurs, parts of the system may still be live. Touching live parts and cables results in death or lethal injuries due to electric shock.
- Disconnect the product from voltage sources and make sure it cannot be reconnected before working on the device.
- Only touch the cables of the PV modules on their insulation.
- Do not touch any parts of the substructure or frame of the PV array.
- Do not connect PV strings with ground faults to the inverter.
- Ensure that no voltage is present and wait five minutes before touching any parts of the PV system or the product.
WARNING
Danger to life due to electric shock from destruction of the measuring device due to overvoltage
Overvoltage can damage a measuring device and result in voltage being present in the enclosure of the measuring device. Touching the live enclosure of the measuring device results in death or lethal injuries due to electric shock.
- Only use measuring devices with a measurement ranges designed for the maximum AC and DC voltage of the inverter.
Schematic diagram of the measurement
Calculating the insulation resistance
The expected total resistance of the PV system or of an individual string can be calculated using the following formula:
The exact insulation resistance of a PV module can be obtained from the module manufacturer or the datasheet.
For the resistance of a PV module an average value can be assumed: for thin-film PV modules approximately 40 MOhm and for polycrystalline and monocrystalline PV modules approximately 50 MOhm per PV module (for further information on calculating the insulation resistance see the Technical Information "Insulation Resistance (Riso) of Non-Galvanically Isolated PV Systems" at www.SMA-Solar.com).
Required devices:
Suitable device for safe disconnection and short-circuiting
Measuring device for insulation resistance
Device required for safe disconnection and short-circuiting of the PV array
The insulation resistance can only be measured with a suitable device for safe disconnection and short-circuiting of the PV array. If no suitable device is available, the insulation measurement must not be carried out.
Procedure:
- Calculate the expected insulation resistance per string.
- Disconnect the inverter from all voltage sources ( > Disconnecting the Inverter from Voltage Sources).
- Install the short circuit device.
- Connect the measuring device for insulation resistance.
- Short-circuit the first string.
- Set the test voltage. The test voltage should be as close as possible to the maximum system voltage of the PV modules but must not exceed it (see datasheet of the PV modules).
- Measure the insulation resistance.
- Eliminate the short circuit.
- Measure the remaining strings in the same manner.
- If the insulation resistance of a string deviates considerably from the theoretically calculated value, there is a ground fault present in that string.
- Reconnect to the inverter only those strings from which the ground fault has been eliminated.
- Reconnect all other strings to the inverter.
- Recommission the inverter.
- If the inverter still displays an insulation error, contact the Service ( > Contact). The PV modules might not be suitable for the inverter in the present quantity.