77Fault

Felicity inverter error 77 (F77)

PV Insulation Impedance fault

Also displayed as F77 on some models.

Fault — the inverter cuts its output and the red LED stays solid until the fault is cleared.

It means the same on every affected model — find yours for the exact fix:

IVGM5KL-P1G1

InverterFault

Also applies to:IVGM6KL-P1G1IVGM7K6L-P1G1IVGM8KL-P1G1

What it means

PV Insulation Impedance fault — PV insulation impedance is too low.

Cause: The pre-start insulation test measured PV-array-to-ground resistance below the safe threshold — usually damaged cable insulation, moisture in connectors, or a missing PE connection.

How to fix it

  1. Check the connection of PV panels and inverter is firmly and correctly
  2. Check whether the PE cable of inverter is connected to ground
  3. Seek help from us, if can not go back to normal state.

Source: Felicitysolar IVGM Series Hybrid inverter Instruction Manual.pdf, p.55

T-REX-50KHP3G01

InverterFault

What it means

PV Insulation Impedance fault — The insulation of the PV string is abnormal.

Cause: A fault has been detected in the PV input stage — usually a short, ground fault, or isolation failure between the PV array and the inverter chassis. Wet connectors, damaged cable insulation, or moisture in a junction box are common causes.

How to fix it

  1. Disconnect the PV strings and measure insulation resistance between PV+ and ground, PV- and ground, and PV+ to PV-.
  2. Any resistance below 1 MΩ indicates moisture or damaged insulation.
  3. Inspect MC4 connectors for water ingress.
  4. Reconnect each string one at a time to isolate the faulty string.

Source: T-REX-50KHP3G01-user-manual-.pdf, p.48

Frequently asked questions

What does error 77 mean on a Felicity inverter?
77 means: PV Insulation Impedance fault. The pre-start insulation test measured PV-array-to-ground resistance below the safe threshold — usually damaged cable insulation, moisture in connectors, or a missing PE connection.
Is error 77 a fault or a warning?
77 is a fault code: the inverter cuts its output and the red LED stays solid until it is cleared.
How do I clear or fix error 77?
1. Check the connection of PV panels and inverter is firmly and correctly; 2. The exact steps for each affected model are listed on this page.

Related error codes

Other codes on the IVGM5KL-P1G1

All IVGM5KL-P1G1 codes

Other codes on the T-REX-50KHP3G01

All T-REX-50KHP3G01 codes

Prefer the full written guide? Read the complete Felicity inverter error-code guide

Compiled from official Felicity user manuals. Always consult your device manual and a qualified technician before performing repairs.