Originally Posted by Pamlicotraveler
I would like to know the real cause, and am perplexed that my 30 AMP fuse in the circuit hasn't blown, but really, again, that isn't the issue.
A high resistance connection can create enough heat to burn an entire marina and never trip a fuse or breaker. This happens more than should in "twist-lock" shore power circuits. You could be passing 20A through a termination that, due to condition, can really only handle 1A and create some really, really high heat, enough to melt the switch.
Here is a very high amperage Class T fuse holder melted due to incorrect lug stacking
which resulted in high resistance. The fuse never tripped because the largest load was nowhere near the fuse or fuse blocks rating but the terminals were stacked so as to create some serious resistance and heat. Not the fault of the fuse holder but rather the terminations and incorrect stacking of them that lead to the high resistance.
Here is a situation where a DIY tried to crimp a terminal designed for multi-conductor wire, to solid conductor land grade wire, on a hot 120V feed. It created high resistance and began to melt the terminal and physically discolor the terminal it got so hot. The main breaker, 30A, never tripped, as this boat could not draw more than 16A. This is not the fault of the terminal, you just don't crimp solid conductor wire..
Here's a 50A rated shore cord from a boat that could barely pull half the circuit breakers 50A rating. This is caused by a high resistance connection creating immense heat that would have never tripped the breaker.
Here's a Scotchlok that had high resistance, and began to melt, at amperage's well below the circuits 10A circuit breaker rating.
And here a DIY tried to crimp this alternator wire with pliers
. The wire to terminal junction created enough heat to begin physically melting the diode isolator at well below its amperage rating. That wire was also red.... Focus on the color of the actual terminal... All this heat developed at amperage's well below the isolators rating.