DC fuse blowout

[Lionscourt]

I was asked earlier this week to look at a solar system on an office/warehouse that had stopped working (not my install). The strings all come into a Fronius DC box on the roof. When I opened it up it was pretty clear why the system had stopped producing:



I'm looking for opinions on what may have caused this so it won't happen again. Why are 3 of the sets of fuses blown but not the fourth? Could lightning have been involved, or was it something more mundane?

 

[SibertSolar]

Direct, or induced, surge most likely I'd imagine. I can't imagine that the fuses were rated incorrectly. Any Type2 or Type1 devices fitted to the DC circuit on the array-side of the combiner box? Was the array frame earthed/bonded to the MET? Any damage to the inverters?

 

[Lionscourt]

Thanks for the reply SiberSolar. I still have some investigating to do, but what I know so far: There are no SPDs fitted between the arrays and the box. The panels are spread out in three lots on a metal roof, with nothing earthed back to the MET. The inverters don't appear to be damaged, but I haven't fully tested them yet.

 

[davesparks]

It looks to me like a fuse has failed to clear a fault correctly and caused a flash-over taking out multiple adjacent units.

 

[SibertSolar]

Can you check the remaining fuses to see what size/type/rating they are perhaps?

 

[Lionscourt]

Fairly certain they're Littelfuse 15A Midget Fuse rated at 600V, at least that's the partially-empty box I was given by the client.

 

[SibertSolar]

Ok, doesn't sound like gPV fuses to me....do you know what the panel spec is, and the string config?


Sent from my iPhone using Tapatalk

 

[Lionscourt]

They are labelled as "Fast Acting gPV Photovoltaic Fuse". I don't have the panel or string info at the moment.

 

[mechelec]

Lightning strike ? Seen it before.

 

[Lionscourt]

Anything that can be done to prevent it, assuming it was caused by lightning? Would having the array earthed back to the MET help to prevent a blow out like this?

 

[Gavin A]

erm, is that 4mm2 cable used as the link from the fused combiners?

fuse combiners that look to be combining 5 circuits, each running at say 8 amps = 40amps running through a single 4mm2 cable continuously for hours on end.

Assuming that this is a system with standard mono / poly panels and not something like solar frontier thin films, then the answer to the question is incompetence (I assume it's clear what I'm getting at).

Also probably not tightened fully on the burned out sections would be why they burned out rather than the left hand neutral combiner.

 

[saggers]

Could be a loose connection overheating. I've seen this before on normal electrical circuits and the heat seems to spread to connections close by.