Intermittent DC String Fuses Blown

[APS Solar]

I have a number of older (and newer) string inverter based systems where I use an Outback or Midnite Fused Combiner box as well as string fuses inside inverters (like SMA or Fronius). I always make sure the fuses are sized properly per solar panel specs. I have noticed that over time I will have a blown fuse on one of the strings. I replace the fuse and the system works fine for many years (doesn't re-blow the fuse). I notice this especially on older systems where the customer reports lower system performance. What in your experience causes string fuses to intermittently blow over time?

 

[GoldDigger]

It is possible that the contact between the fuse and the holder is deteriorating over time, especially if the contact pressure is insufficient. Resistive heating could contribute to the fuse blowing.

 

[APS Solar]

Is there any way to prevent this? I use Bussmann fuse holders. All I can do is make sure my guys fully seat the fuse