Wires are sized based on the amps that will flow through them, and the length of the wire run. If the load is heavier than the wire can handle, it will get very hot and potentially cause a fire. Fuses and circuit breakers are used to protect the wiring. So when an appropriately sized wire somehow gets short circuited or gets too heavy of an electrical load, the fuse breaks or the circuit breaker trips to shut it down. That all assumes the connections are sound. However, I found out the hard way that when a connection is made with a weak or poorly made wire crimp, a heavy load that the wire can typically handle creates resistance and thus heat. The heating only makes the connection worse and the situation escalates itself. That is what happened to Fiddler’s inverter cable as seen below.
The weak connection got so hot that it melted the sheathing. The load was not enough to trip the breaker or the fuse, but it was a heavy load. During an engine room check I noticed an odor that was definitely electrical. I thought at the time that the inverter was just working harder than normal and I monitored its operating temperature on the remote panel in the pilot house. The temperature returned to normal. The inverter continued to work fine and I no longer noticed the odor in the engine room. But while doing some recent routine battery maintenance I noticed the melted wire, and then it all made sense. An unusually heavy inverter load exposed the weak crimp connection, causing it to heat up to the point it burned and melted the sheathing. No other connections were affected. So what was the heavy load? Well, Fiddler has a convection microwave oven and we were using the convection feature to bake a pizza while at anchor. The convection feature draws a lot of amps over a long period of time while the pizza bakes. Fortunately there was nothing combustible near the heat and no disaster. But I am glad the weak connection was exposed. Of course, it is now repaired and the crimped connection is very strong. But I will certainly be monitoring it the next time we bake a pizza at anchor. Or I might use the propane oven instead.