This was discovered on top of a wooden arbor that attaches to a garage. 150 W on this run of #14 wire. looks like there could have been some arcing. Wire nut was melted to the point that the back side shaped to the wood grain. The oxidation on the wire makes it look like a portion of the conductors were exposed outside the wire nut... Funny thing is, I saw a guy "fixing" this about two years ago. He was replacing tape and Scotchlok connectors with these. I was doing irrigation repairs on the job and the client didn't yet know I also did lighting work. Wired in to a buck-and-boost transformer (which I replaced). Didn't look closely to see if there was a fuse or a breaker on that TF, but I'll check today. All the splices were replaced w/ Ace connectors and wire changed to #12 to the first split.