Along those lines, Dec. 2019 my stepmom up the road called me, said her small heater in the bedroom went out and she could smell something.
Below is a picture of what happens when you daisy-chain outlet to outlet and use the push-in wire holes in the back instead of forming a loop in your wiring and using the side screws. Those back push-in holes have like knife-blade to grab the conductor in a small area when compared to a good loop on the side screws. The voltage drop from that poor connection when using a 1500 watt radiant heater caused enough heat to burn the insulation as the heat conducted down the wire. This has been heating up for some time, as the copper has turned orange in color, an indicator it has lost its annealing and ductility, making it brittle. Further evidence is the ivory thermoplastic has turned brown.
I had to move so far down the hot and neutral conductors to cut out the brittle part I had to make a short pigtail, wire-nut and tape and come up to a new receptacle, which I then connected with loops and side screws. I also went upstream to the other 2 receptacles, replaced them with new and wired to utilize the side screws.
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