This reminds me of the time I happened to be at a warehouse where an industrial motor control panel was being decommissioned. In the center of the panel is a large breaker, which was dutifully opened (ie powered off) before work commenced. But bizarrely, someone in the past managed to tap power from the supply-side of the breaker for some sort of monitoring sensor inside the panel. So when that circuit was cut through, there was a loud bang and the overhead lights went out.

No one was injured, although everyone was jumpy from the inadvertent light-and-sound spectacle. And a set of cutters gained a 12 AWG-sized (approx 4 mm^2) hole.

I may have misremembered some details, but my takeaway as a non-electrician was to 1) never assume a breaker handle at face value, and 2) don't assume the prior person made sane choices.

forgot to check the breaker?

You lent them out?

I swear I heard it when I saw the picture. I'm not an electrician, but that's why I always call electricians instead of doing it myself.

Steel is real, not all wire is created equal. Someone borrowed the soft jaws and chewed the wrong chow.

That looks a bit deep to grind, but maybe. I grind the back face of my higher end diagonals to sharpen and extend their life.

You found the breaker.

involuntary welding

You made a small notch to strip cables ? LOL

You tried to bite the cable, and the cable bit back?

You changed the strings on your guitar.

There was a hidden layer of concrete in your steel cables

The dog got a hold of them.

oopsie happened

You didn't LOTO

Forgot your strippers and made due anyway