# ABB/FIMER inverter Riso Low (E025): what it means and what to do

"Riso Low" on an ABB/FIMER inverter means that before connecting to the grid, the inverter measured the insulation resistance of the solar array to ground and found it below 1 megohm, so it does not connect. FIMER logs this as error E025, although that number is not shown on the display. Common causes include damaged panels, moisture in junction boxes, and poor connections, and the check has to be made by a technician.

## Common causes

- One or more damaged solar panels.
- Panel junction boxes that are not sealed properly, letting in water or humidity, or humidity inside a junction box.
- Connections between panels that do not fit perfectly, or poor-quality cable joints.
- Unsuitable or damaged surge arresters on the DC side, outside the inverter.

## Safe steps to try

1. **Keep clear of the system** FIMER warns that trying to fix a malfunction yourself is extremely dangerous without the right training. Do not open the inverter, a disconnect, a junction box or any conduit, and do not touch the panels, racking or wiring.
2. **Note the time of day and the weather** FIMER says the insulation measurement is strongly influenced by environmental conditions and must be repeated under the same conditions in which the error occurred. Note whether it appears in the morning, after rain, or clears later in the day.
3. **Book a technician** The technician measures the array's insulation resistance with a megohmmeter. FIMER's rule is that a reading below 1 megohm needs the array checked by a technician or installer; above that, with the error persisting, the next step is FIMER customer assistance.

## When to call a professional

Call promptly, and certainly if Riso Low keeps returning. It means the insulation between the solar wiring and ground is too low somewhere in the array, and only a technician with test equipment can find where.

## Frequently asked questions

### Why does Riso Low come and go?

FIMER notes that the measurement is strongly influenced by environmental conditions. Moisture getting into a junction box or connector can lower the reading in damp weather, and the error can disappear once things dry out. The underlying weak spot is still there.

### What does the GFI light mean?

FIMER uses the GFI LED to show that a leakage to ground from the solar array has been detected, causing the inverter to disconnect from the grid. FIMER advises having the system inspected by an installer if this happens repeatedly.

Canonical page: https://otovo.com/repair/abb/riso-low