Fronius Error 475 DC Isolation Problem

Hello, I’ve searched the forum and can’t find any reference to this problem that I have with my System. My system has been operational since Feb 2018. I noticed in Dec 2021 that solar generation was not starting until noon or later and prior to startup it was showing the Error 475. I went back and discovered the delayed generation started in Jan 2021 (no problems in prior years). The error occurs mostly during the foggy or wet days and disappeared completely after Apr 2021 only to return in Oct 2021 when we had our first rain and subsequent foggy days. I’m pretty sure I have a failing panel(s) with low resistance during wet or moist periods. My solar service folks have been here twice and seemed to think that firmware updates would solve the problem - nope. I’m starting to keep track of the Isolation Resistance on the Fronius Primo display. It showed 1.4 M ohms during the failure and 1.6 M Ohms when working. I’d like to verify the Isolation Resistance that Fronius uses to determine an Isolation Fault. Also, my panels are LG 300S1C-A5 (300 watt). Has anyone had problems with DC Isolation Failures with their panels and if so, how was the problem tested and fixed.

Hi @kblackw. I did some research and it appears that the STATE 475 message is most commonly associated with an ingress of moisture somewhere.

Do you have more than one string on your inverter? If so can you compare the DC output(s) of the two strings using Fronius’ solar website. If you have multiple strings you may be able to compare them, over time, for a loss of performance.

Have you been able to safely physically examine any exposed DC cables, DC isolator [ Especially a rooftop DC isolator if you have one ] and panels for any sign of water ingress, corrosion, damage?

I think you will need to go back to installer or a competent and licensed person to sort your problem out.

STATE 475 error on Fronius Galvo, Primo and Symo solar inverters.

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