Philip,
I had one about 5-6 years ago where the home was vacant and the "owner/seller" let me in. No lights were on and the *service main* was off.
The seller says, "it's ok to go ahead and flip the main disconnect to turn on the power. I thought I had left it on, but I gess I turned it off to save energy."
Well, I reluctantly go flip the main (seller said--"it's ok"), lights come on and I head around to each room and turn every fixture on (as I always do) to fully illuminate the home and put as much of a load on the panel as I can to try and see if there is any nuisance tripping.
I got about 90% of the lights on when some of the fixtures started going dimmer. I thought... whaaaaa-t now! I go to the service panel and low and behole... that sucker had several conductors glowing like the wire nut in your picture.
Now, in the mean-time, the seller had managed to walk-out and drive off. Since I had his number and the number of the buyer, I called both. The seller comes back over and says, "What did you do?" My reply was...
I tried to burn down the house by using the existing wiring system you have installed. The seller then says (at the same time the buyer is walking in the front door), Bull-S#!+!! All I told you to do was to flip the breaker, not to touch anything else.
About that time the buyer asks, "what's going on". I told him that we almost had a fire and the panel was, "of the glowing-in-the-dark type". Buyer looked at the seller and said, "you told me that you were going to take care of the wiring issue that you knew you had!!"
After a few choice words to the seller, I left and then called the city code compliance inspector and the fire marshall. I drove by the home two days later and the home had been red-tagged, by order of the Fire Marshall.
Rich