I noticed on Thursday last week that the peak solar output was down about 10-12%. Ran over to my 2 central inverters and sure enough, one was producing 25% less than the other. Thought about this for about 5 minutes and realized one of my strings of panels were not producing. I have 8 strings of 9 panels each and the the fused combiner is in my attic. Well my left leg is in such bad shape I can't do that climb right now, so called an electrician recommended by my neighbor. My regular guys will not touch the DC side of the solar system.
The electrician showed up @ 9:30 AM before stuff got really hot up there. Sure enough, the combiner had a mix of 10 amp and 8 amp fuses installed, one of the 8 amp one showed open. 8 amp fuses are kind of close to the 125% rule for fusing, so I had them replace all the 8 amp fuses with 10 amp ones. Voila, back in full production.
The original installers probably didn't have enough 10 amp fuses with them and a pile of the 8 amps ones on the truck. Lazy bastards!