Electricity Gone Wild

I've seen that one before. The arc was caused by the failure of a circuit breaker to open before the switch opened.

At ordinary end-user voltages, a switch is designed to interrupt normal load current, while a circuit breaker is designed to interrupt fault current (which can be several orders of magnitude greater than normal load current).

At transmission line voltages, a switch isn't intended to interrupt any current at all; this is the task of a circuit breaker. In that service, a switch is used solely to change the configuration of a network. First, you trip out the breakers to de-energize the circuit, then set switches to the desired positions, and finally reclose the circuit breakers to re-energize the circuit.

No time to get the marshmallows, dagnabbit.

Like Ktesibios says this is not a normal arc for this type of equipment.
Seeing that my knowledge of electricity goes about as far as don't touch it and it powers my PC I did a little search and found someone who analyzed this video and explained what went wrong.
www.wiseguysynth.com/larry/day.htm

This story makes me want to set up a Jacob's Ladder in our yard. I haven't talked it over with Jodi yet, but I'm sure she'll be just fine with it!

Jason, Ben set one up for Halloween a few years ago. Indoors, though, so the parents couldn't get all stupid and touch it.

Neon transformers are the best to use for small Jacob's ladders since they are designed to limit short circuit current. I used to have a few 12KV transformers lying around (from certain radio equipment) and accidentally struck a spark one day - that was not pleasant. But even neon transformers need the rabbit ears etc. safely away from where people can touch them; these transformers are still lethal.

I like the gigantic 3-phase ladders that you can see at some places.

Also keep in mind that the electric arc 'fixes' nitrogen, producing N2O and nitric acid; if you have a well sealed enclosure you'll see a lot of corrosion from the acid; on the other hand ventilating the enclosure screws with your spark.

At my old workplace, a fellow worker had many stories from his time working at a power company. My favorite was the time he had come to a substation to investigate a major failure. There had been flames and sparks and everyone had gotten out of there fast (thankfully). He was interviewing the people who'd been there, and was talking to the supervisor.

"So, what happened?"

"Well, there was an explosion, a lot of arcing, and we all ran for the door."

"And you fell down, right?"

"What? No, I just ran right out with everyone else."

"You're sure you didn't trip or anything?"

"Yeah, I'm sure. Why?"

"Because there's a footprint on the back of your shirt."

Saint Elmo's Footprint.