We have ones like that at work for doing generator switchover - talking about Aggreko 20-foot shipping container generators providing hundreds of kW to power a pair of UPSes the size of a full-size Ford Transit, not your cute little 130-from-Hofer-pull-the-string-puttputtputt genny ;-)

You pump up the handle to charge a pneumatic cylinder and when you cut over it throws a set of three contacts about the size of a first-gen Kindle from one side to the other, switching from incoming mains to genny power in about 1/100th of a second.

It goes with a hell of a bang.