In this case it was a very early and heavy duty version of the Mitsu 3,000w inverter. It is quite a large unit and appears to have 2 inverters in each one of the double half cases, so a lot of wires connected to the positive terminals at the end of the casing. One of the positive terminals touched the outer casing and rubbed through the heat shrink, the inverter was mounted to the wooden floor so there was no connection to negative through the body work so no indication that the inverter body was actually plus 12vdc. Everything worked fine till I plugged the long extension lead coming out of the RVD into the caravan inlet socket, but a few mins later large clouds of smoke poor out of the inverter.
The earth lead through the extension cable connected the earth pin on the caravan inlet with the earth pin in the inverter, the caravan earth pin is connected to the caravan body, the earth pin in the inverter is connected to the inverter body. Because the cable was so long the voltage drop was enough to not create a dead short but rather heat up the earth conductor cable, the thinnest was in the inverter so it glowed red hot and burnt off all the green and yellow insulation, that was all the smoke. There was not enough current to blow the fuse, it was DC power so didn't trip the RVD, it just fried the earth cable. An easy fix to what looked like a terminal case of escaped smoke.
There was a similar issue with a Victron Phoenix multiplus. Inside the inverter there is an L shaped bus bar that connects the charger positive to a 400 amp mega fuse and the inverter positive inlet stud. The negative cable enters through the inverter base and over this bus bar and on to the negative stud. The whole unit connected up fine and ran for a number of hrs, then the lights and power went out. The 300 amp mega fuse had blown, at first I thought it was an over load failure, so I attempted to replace the fuse with a 450 amp unit.... the arc blew the washers above and below the fuse into a molten metal spray and removed the finger prints from 3 finger tips as I tried to get it back off, the silly things you do in one of those spare of the moment situations.
The problem turned out to be caused by a very sub standard cable crimp on the negative done from the caravan factory had finally rubbed through the heat shrink and made a connection with the positive bus bar, I'm guessing it was the first time the inverter had enough battery power to work under full load so the added heat was enough to create the failure in the heat shrink. Another easy fix, make a proper cable crimp and space the busbar lower and negative terminal higher so there was an air gap between the 2.
In both cases, nothing to do with anything that had been done during the job, but an issue that wasn't apparent before but certain was after. Sometimes its the little things you don't look at because it all worked before that catch you out.... and they ask why the job takes so long
