ISO on a GoodWe Technologies Co., Ltd. GoodWe ET / ET Plus+: ISO failure (Isolation Failure) - PV ground cable not/poorly connected

What it means

The manual says: ISO failure (Isolation Failure) - PV ground cable not/poorly connected.

Part involved: PV insulation to earth.

Likely causes:

• PV ground cable not/poorly connected; DC cable insulation damaged; N & PE poorly connected; occurs on rainy days/early morning/sunset with high humidity. | Troubleshooting: Connect strings one by one to find faulty string; check DC cable insulation; check N-PE voltage (<10 V); check panel earth bonding.

Is it safe?

The inverter stops until the fault clears or is reset.

Resetting itself: unknown.

Manual reset: Restart per GoodWe troubleshooting guide.

What you can check

• Check the inverter LEDs (FAULT LED on = fault) and read the alarm in the SEMS Portal app or SolarGo app; note code, message and time for your installer.
• Do not touch panels, DC cables or connectors.
• Note whether it clears later in the day (humidity) - tell your installer either way.

What the engineer will check

• Per-string insulation test; inspect DC cable damage; N-PE voltage; earth bonding.

Who to ask for: GoodWe-trained installer / MCS PV & battery installer.

Certification: Qualified electrician (BS 7671; MCS-certified PV installer for work on the PV array/DC side).

What you might notice

• Error code shown on inverter or app
• Solar panels not generating at all

Sources

• Troubleshooting Guide Hybrid Inverter (ET, ET PLUS+, EH, ESA, ES, EM, EHB, ES G2; BT, BH, BP, SBP) - EMEA ↗ · V1.0-2023-03-10 · page 19 · Reviewed 24 September 2026

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 24 September 2026