cable burned ?

[dbz864]

Hi, Got a problem with electrics, nothing much was working in a van, last owner had bodged a few cables in to try and solve a problem. I found that no power was going to the aux battery, the split charge relay was working but it wasnt getting power to battery, after many hours i found under the cab carpets a very thick cable had kind of burnt through just in one spot and had melted well into a very thick 2 core cable that had come from a on board zig charger, no screw, no welding had gone into cable, the electrics are original autosleeper, the cables are very heavy duty. What would cause this in just one spot? Any ideas?

[Mr Bean]

My set up is home brewed and if I let my leisure battery get completely flat like if I left something switched on, then my 30 A leisure bus bar fuse will blow presumably as there is much more than 30A available from both the vehicle battery and in my case a 90 Amp alternator.
I should imagine that a severe overload or short current could easily overheat a cable at a weak spot along its length. Although you indicate that the thickness of the cable looks adequate. You don't indicate whether the cable actually open circuit? A circuit diagram would enable a more informed analysis if available.
CS

[dbz864]

thanks.. Its the cable that comes from the split charge relay to the aux battery. completly "blown/crumpled/burnt in half, left it in 2 halves. Very thick cable. Just dont understand why it went in the middle? I will try and put a photo up.

[Mr Bean]

Wow! It takes a whole lot of current to burn out a thick cable and I suspect there was no fuse between the relay and whatever supplied the return path to the van earth (battery negative in negative earth systems. This could have been a faulty device with no fuse or (a nail in place ) or more likely, a short to earth (vehicle chassis or bodywork). I have a 90A alternator fitted and in theory at least there will 12 X 90 = 1,080 Watts available in a fault condition.

It is possible to find a high resistance section of a cable which could be a manufacturing/handling/installation fault and in these circumstances it could heat up and break connection melting the insulation on the way.

You need to track the dead end back to the Zig charger and go from there looking for a short to earth or or wrong fuse which may have been fitted to keep a duff accessory from blowing.

There is a very remote and unlikely possibility that the fault current came from the leisure battery but I struggle to put this scenario together without a circuit diagram.

There are plenty of people running Zig boxes of one type or another so maybe one of them could chip in as I am flying by the seat of my pants in terms of ZIg equipment.
CS