Not only is no circuit fast enough to disconnect in time, lightning isn't AC/DC. It's electrostatic. Which means it carries and induces potentials that can jump further than your power usually can. So it'll bridge the connection in even circuits that were already disconnected.

sadly it won't work ... the lightning will go around the switch through the air, just like it did all the way down.

Edit: spelling

So if you unplugged your computer the lightning would still find its way, through the air, to your computer?

It could if it was still part of the lowest resistance path to ground. Electricity is like water, it wants to flow from high potential difference to low potential difference.

Lightning (as far as I know) does not have consciousness and is not out to get your computer!

The parent post was talking about putting a automatic switch in between the power supply to the house (ground active neutral) and switching it off when lightning struck, the problem there is that the switch will not do much if the lightning air gaps around it.

Isn't it more likely that the current will go from one terminal of the now unconnected cord to another terminal of the same cord?

It all depends on the what is the shortest path to ground.

Ground is also a relative term for a lightning strike.

When lightning hits the ground, a potential field emanates from that point. The further out the closer to 0V the potential difference is.

As such it depends on where the strike is in comparison to the house, your wiring, where your house is grounded etc.

For example, if the grounding point on your house is very close to the strike, your house ground will be raised to the voltage of that point away from the stike.

The path to 0V may be through your active wiring, your powesupply, the house frame or the water pipes.

So yeah, hope that helps

Good luck breaking a circuit when dealing with lightning discharge conditions.

That is unless are okay buying oil immersed equipment the size of a fridge. And that’s probably not enough, either.

By it's very nature, lightning is high enough voltage to leap an air-gap

You only have to make the gap larger than the gap to a well-grounded terminal.

You're assuming it won't bifurcate and jump across both gaps, which is entirely possible.

You're a true inventor with a perfect grasp of the principles, that's basically how circuit breakers work! The challenge is to predict the future: sense how high the voltage pulse will rise, before it overloads. The speed of light is hard to exceed, at least as we currently understand. The charge will look for a shorter path, so if it can find a way around the long cable, the lightning will probably strike there instead.

Now here's one for the engineers. We can tell the future. Musicians change tempo before singing the next verse. ADS-B data tells us when there's a plane coming. Could a "smart" surge protector include a measure of ground noise, to sense local charge differentials, and guess that the next spike is probably lightning rather than a typical mains arc? More sensors yes, but increasing protection only when expected would possibly improve the feedback loop.

No relay in the world is going to switch fast enough for this. I'd love to be proven wrong though.