So many things we hear about what happens when you buy cheap.
Picture in question shows a 'disappeared' Solar DC switch. Not something you want on your system. As case in point, this can happen for a number of reasons:
1. Cheap nasty switch eventually fails - sparks, arcs, overheats, and in this case catches fire. Nothing you can do other than have a decent quality switch installed in the first place. Will the 'cheapest price' system have a decent quality switch? No prizes for guessing the answer is a resounding NO!
2. Maybe a reasonable switch was installed, at least one that has a few more years on it before it fails of its own accord. Now suppose the box containing the switch on the roof admits moisture - it only has to be seriously damp air, or just a half-dozen drips. Now this water will alternately evaporate and condense inside the switch-box on the roof AND after a period of time it will migrate down to the switch under the inverter! On a cold, damp morning the beads of water connect across the internals of the switch, and in the best case - the inverter will detect this, shut-down, and report a fault. In the worst case - the inverter might switch-off, but the water is still short-circuiting the array of panels.
Result is the same - worst case the switch on either, or both, the roof and under the inverter, do catch fire.
3. Once again, suppose a reasonable switch was installed, BUT the designer did not understand the manufacturer's datasheet! Sounds crazy, but the switch datasheets show the primary rating of these switches in European format - and not (or at least not clearly) in the mandated Australian format. Designers should be able to work this out, but I have encountered some situations where this was not the case. It means that the switch in effect only has *HALF* the rating it should for the given array. Eventually, the switch will succumb to failure following maybe a few years of heat/cold/moisture cycles, and will most likely fail just when it is being switched off because of an earth (eg moisture) fault.
This 3rd point is less likely, but is definitely out there in my opinion. Thats why we always say to turn off the AC Isolator first - that way strong DC current is not being interrupted, thus stressing an underrated switch.
What is peace of mind regarding decent switches worth?
Sales folk of cheap systems have no choice to tell you their switches are "of the highest quality". Incidentally, what happens to all the "low quality" switches then? Well, they may well be subject to a government safety recall! I wonder how many rock-bottom cheap solar companies got caught on the 3 or 4 recalls of bad switches that have happened so far?