SMA [3701] fault codewhat it means and how to fix it

Event 3701 is SMA's residual current or excessive leakage current event, internally named EvtdAmpMax, and the useful thing about it is how precisely SMA distinguish it from the insulation event that sits nearby in their numbering. Their published explanation is that a residual-current monitoring unit in their transformerless inverters detects potential ground faults by monitoring alternating and direct residual currents, and that sudden jumps of thirty milliamps or more will disconnect the inverter from the grid. So the two events answer two different questions at two different moments. Event 3501 measures the insulation before the inverter connects and stops it starting. Event 3701 watches while it runs and trips it mid-generation. Knowing which you have tells you something useful about the symptom you are seeing: a system that never starts in the morning versus a system that drops out during the day are different findings from the same underlying family.

The thirty milliamp figure is worth pausing on, because SMA say why it matters in their article on the event itself: residual currents greater than 30 mA can be life-threatening, the inverter disconnects from the utility grid immediately after the limit value has been overshot, and as soon as the values are back in the permissible range again, the inverter automatically switches itself on again. That last sentence is the one to hold on to, because it means a system that tripped and came back has not been repaired — it has been allowed to reconnect. Thirty milliamps is also the same order as the residual current protection used to protect people from electric shock in a domestic installation, and it is a small fraction of what the array is capable of delivering. The monitoring exists because current finding an unintended path to earth is the signature of insulation breaking down somewhere, and the same conditions that produce it can produce a shock hazard on the structure.

SMA's corrective measure for both events is identical and short: contact your installer for further investigation. They also link the events to the light on the unit, which is the only indication most owners will see, since modern SMA inverters have no display. 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, and the electrical insulation from the PV system to ground is defective or insufficient. Their strong recommendation covers the whole family, 3501, 3502, 3503, 3601 and 3701 together: have the PV system inspected by a qualified person.