My gosh! I am so glad that you are OK and your house did not burn down.
We have seen far too many of these on the forum. It happened to a close friend of mine here locally. I very much appreciate you posting this here as a warning to others. I have been considering gathering all the pictures of the meltdowns I have seen and putting them in one place to underscore to folks how critical it is to do this stuff correctly.
Some questions for you:
What brand of receptacle was that? Leviton? [Yes, a Leviton.]
How long had it been in service? [About 7 months.]
Any idea why the branch breaker did not blow? Or did it *also* blow? (what kind of panel do you have? - not like a defective Federal Pacific one?). [Branch breaker also blew. I cannot tell the brand of panel, but we recently de-rated the panel to 175 amps as part of a solar panel installation-certification last April. The panel worked as it should to protect the house, and I’m glad we de-rated because who knows what an additional 25 amps might have allowed.]
The Wall Connector is a great idea. I have not seen any picture of a melted one yet (not that you could not have a loose terminal on one, but they use better quality clamping connectors than the screws on the low end receptacles).
Glad you are OK!