Why is my GFCI outlet completely charred if the breaker didn't trip?

That’s a classic case of a high-resistance connection rather than a traditional overload. When a terminal screw isn't torqued down properly or a wire isn't seated right, it creates a small gap where electricity has to fight to jump across. This generates massive amounts of heat at that specific point. The scary part is that it can stay well below the 20-amp threshold of your breaker while still getting hot enought to liquefy the plastic casing. Breakers are essentially dumb devices; they only care about total current flow or a dead short. If that connection is pulling 12 amps but dissipating half of it as pure heat becuase of the resistance, the breaker thinks everything is fine. You’ve basicly created a tiny, unintended space heater inside your wall box. I've seen this happen with back-stabbed connections expecially, wich is why most electricians avoid those and only use the side-pressure plates or wrap the wire around the screw. There is also the possibility of a manufacturing defect in the GFCI’s internal bridge. I've run into entire batches of units that woud cook themselves with zero load plugged into them. If the internal relay or the sensing electronics fail, they can arc internally and melt from the inside out. Since the device is already charred, the evidence of which internal component started it is prolly gone, but the outcome is the same. You absolutely need to cut those wires back untill you find **clean, shiny copper**. That heat-damaged wire is brittle and has much higher resistance now; if you just scrape it and re-attach it, the new device will fail the same way. Use a high-quality **commercial-grade** replacement. They have beefier internal contacts and can handle heat dissipation better than the cheap residential versions. Also, check the wire nuts in the back of the box to ensure the ambient heat didn't compromise those connections too.

I had the exact same mess in my garage last year. It turned out my old fridge was pulling just enugh to cook a loose screw but not enough to pop the 20-amp breaker. I learned the hard way that 'hand tight' isn't enough. Now I use a torque screwdriver for every outlet I install. It feels like overkill untill you see charcoal in your wall. Also, make sure you aren't using those push-in connectors on the back. I only use the side screws now and give every wire a real good yank before I close the box. If it moves even a hair, I tighten it again.

Spot on. I've seen this exact thing in garages becuase of the humidity cycling—expanding and contracting those copper connections over years makes even 'tight' screws come loose. One thing people miss is that the heat doesn't just stay at the terminal; it travels up the wire like a heat sink.

defintely pull some extra slack out of the wall if you can. If the insulation feels stiff or 'crunchy' even six inches back, you've gotta keep cutting. If you don't have enugh slack, you might need to add a junction box further up the line to run fresh wire, because that cooked Romex is a fire hazard waiting to happen again.

Update: Thanks for the advice. That point about the heat traveling up the wire as a heat sink realy clicked once I started stripping things back; the copper looks pretty brittle further up. Since you mentioned humidity cycles loosening things, should I go ahead and pull the other outlets on this circuit to check them? I'm definitely picking up a torque screwdriver before I wire the new GFCI in.