Break away cable getting red hot where it connects to the car

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May 15, 2023
Thinking this through (really need to draw a schematic) There must be a second isolator that has disconnected the incoming supply earth (Car -Van) possibly if the main power control unit is shut down? there should be earth bonding, its odd to isolate just earths, or there is an earth fault in the van?

Assuming the former is the case and the Orion unit is isolated, the van is earthing via the break away cable. If all was happening is the leisure battery being charged from the cars alternator, I'd still be surprised if the current was high enough for a long enough period for the cable to get hot?

Assuming the van has a Alko hitch it also means that the friction pads in the ball hitch prevent any metal to metal connection, and a car to van earth.

I'd suggest its worth looking at the way the Orion unit is wired in relation to the main power control unit, and how any isolation works in the van, possibly Orion unit was a retro installation by someone that didn't fully understand van electrics?
Jun 20, 2005
Was one of the neg cables not connected? what was the rogue cable touching to cause the current flow and then return via the breakaway? Fascinating ??


Deleted member 27623

When i checked the current it was only very low around 20ma, but it was arking on the connector, which of coure after a three hour journey caused it to get hot. My caravan actually has three hard wired earths, all run through the towing connector cable, but one of them (which was the onboard PDU negative return) was the one that was not present due to the isolated DC/DC charger. It was only by chance that someone noticed the onboard PDU LCD screen display going on and off when you attached and removed the towing wire that gave us the hint. I then checked the J5 connector on the PDU for continuity back to the front plug cable and there wasnt any! further investigations led me to the charger and once I realised it was an isolated version, I realised what was happening. Not an every day type problem by any means!

Deleted member 27623

Thank you for keeping us informed.

I am amazed at how what you have described has occurred and especially how the route back to the tow vehicle for the DC to DC converters 0V line found the breakaway cable to be a lower resistance than the existing wiring harness.

It's correct practice to ensure that the mains earthing and the negative of the 12V system are hard wired back to the their respective sources. The metalwork of the caravan and its chassis may also be connected to both the mains earth in the consumer unit and the 0V of the 12V system, but becasue there are different parts of the caravans metal some of which may not make a secure reliable electrical contact to its surroundings, it cannot be used as the primary route for mains earthing or the 0V returns.

It sounds as though the DC to DC converter was not installed according to good wiring practice.
It had actually been installed correctly, it was just the wrong type of DC to DC it should have been a none isolated version. And to be fair they look very similar. I just linked the negatives across in the end to put in continuity, so in theory the positive is still isolated but the ground is not.
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