Thoughts on why a direct short doesn't always trip the breaker?

I've seen this happen more than once with those thin Harbor Freight or Stanley tapes. What most people forget is that a standard 15-amp or 20-amp breaker—expecially the older Square D QO or Siemens ones—usally needs a massive spike, like 5 to 10 times its rated current, to hit that magnetic trip instantly. Steel is actually a pretty mediocre conductor compared to copper. Between the resistance of that thin tape and the fact that the metal vaporized almost instantly, the "fault" probaly cleared itself before the breaker's internal mechanism coud even move. It’s basially a high-speed fuse at that point. If the spark blew the path open in a fraction of a cycle, the breaker just sees a temporary surge that doesn't quite cross the threshold. I wouldn't lose sleep over the breaker being faulty, but definitely check the tension on the new outlet's contacts so those charger prongs don't sit so loose next time.

Honestly, I’d be a lot more concerned about the breaker than the resistance of the steel tape. Everyone always points to the math of the trip curve, but in my experience working on older residential panels, breakers can and do fail mechanically. If that was a Federal Pacific or an old Zinsco, those things are notorious for "welding" shut or just jamming up internally. Even a standard older GE or Bryant that hasn't been flipped in twenty years can get physically stuck.

I once had a dead short on a 20-amp circuit where a snake bit through a wire in a crawlspace. It blew a hole in the conduit but the breaker never budged. When I pulled the breaker, the internal mechanism was completely seized from years of humidity. Replacing the receptacle is a good start for the carbon tracking, but if I were you, I'd kill the main and actually toggle that breaker back and forth a few times. If it feels mushy or takes any extra effort to reset, swap it out. I wouldn't trust my house to the "physics of steel" when the mechanical safety might just be a dud.

I had a similar pop when a screwdriver slipped while I was changing a cover plate. The tip just disappeared into a spark. I stopped worrying about the panel and just started using those plastic 'outlet shims' or caterpillars to make sure the new receptacles sat flush and tight against the drywall. If they don't wiggle, the charger doesn't sag, and the tape can't get back there. Also, I started buying the $3 heavy-duty spec-grade outlets instead of the 50-cent cheapies. The grip on the prongs is way better, and you won't have that sagging charger problem anymore.

Classic case of the 'pop and clear.' I've had this happen with a pair of needle-nose pliers before. The metal's so thin it basically acts like a fuse and vaporizes before the breaker even realizes there's a short. If you're really worried though, you could always swap in a dual-function AFCI/GFCI breaker. They're way more sensitive to those quick arcing events than the old-school thermal-mags. Probably overkill if the wiring's solid, but it'll definitely give your parents some peace of mind.

Seen it a hundred times back when we didn't have all these fancy AFCI requirements. Back in the day, we’d call that a 'self-clearing fault.' That thin steel tape isn't much better than a piece of nichrome wire; it glows, blows, and goes before the magnetic slug in the breaker even thinks about moving. I remember dropping a fish tape across a live bus on a commercial job in '82—same thing, just a bigger bang and a notch in the steel. If you’re relly paranoid, pull the breaker and check for any soot, but ussually, if it still clicks 'on' and 'off' with a good snap, it’s fine. Just make sure you’re wrapping your terminals with electrical tape on the new install.

Check the date code on that panel. If you're looking at an old I-Line or even a standard Square D Homeline from the 90s, those trip curves are specifically designed to ignore 'nuisance' spikes. You’re dealing with a millisecond event. By the time the magnetic element in a QO120 even considers pulling that trip bar, the steel has allready hit its melting point and the circuit is open. I’ve seen guys dump a whole bucket of 12-2 Romex scraps into a live gutter and the breaker didn't even flinch becuase the arc cleared too fast. Swap in a Leviton 5325-W with some decent tension and call it a day.