Operation of a Knife Switch

To avoid arcing while interrupting higher voltages, a spring-powered knife switch can be used to cut the current as fast as possible. For a mechanical knife switch, this can be achieved by using a spring to connect the knife to the handle. The energy built up in the spring while pulling the handle will abruptly be released when it surpasses the friction between the knife and the clamps.
In this Demonstration, the knife K cuts the current between clamps A and B when the handle H is pulled sufficiently far. The adjustable spring constant defines when the current is interrupted and the release speed of the knife.
This article is mainly of historical interest, since knife switches have long been superseded by other types of high-speed switches in electronic technology.


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