- Really glad for the OP this wasn't the feed line (like other's comments). Also glad he found it prior to using winch in this condition.
- A fuse or CB (like WJCO's) makes a lot of sense for systems that are being used regularly (like police or FF applications)
- Personally, not a fan of remote actuated switch / relays at these current levels for the application in question (I.e. winches) ...I much prefer manual switches with margin
- For an 8k winch, a 300A fuse or CB would be adequate as max draw is just under that (carry spares!)
- Above 8k require a heavier protection circuit. For instance, 12k lb winch pulls 440+ amps. Which brings me to a hypothetical...
Scenario: Assume, instead of "return", OP's "feed" line was chewed through. BUT, he had a 300A fuse (or CB) protection in place. So the new circuit created by the weld of the cable to whatever it was touching would be allowed to feed up to 300A without tripping the CB (or blowing the fuse). Depending upon the quality of the new (unintended) connection, that current could continue for several hundredths of a second before the new connection either (a) melted through or (b) welded further, enabling more current and therefore tripping the protection in place.
Alternately, the cable could hop around, sparking every time it touched ground. This is unlikely, as the current in question would be fairly likely to create a temp weld when it touched something allowing an adequate "return" path.
The consideration for ya'll is: What would several hundredths of a second at just under 300A be capable of in the engine compartment? In my personal experience, the new connection "returned" via the brake line, which in turn vaporized the brake fluid inside, which is what started the fire. (Auto accident root cause, btw.) Power steering fluid would work, too. Not to mention the fuel rails. I don't remember if the vehicle in question had circuit protection or not.
Just a thought...