Writing another post I started thinking about bad installation of kit.
I got called to site once because some 3 phase power monitors were misreading. They were installed with large air con units on the roof of a large office block.
They were installed in IP65 cases. I opened a case and asked the guy, why had someone drilled holes in the bottom of the case. The answer was to let the water out. The cases were IP65 but the wiring conduits were working like water pipes and water was running into the cases. All terminals were corroded.
I guess the water was distilled by the humidifiers otherwise I don't know why the fuses didn't blow. May be they did blow which is why they drilled holes to let the water out.