Rotary-blade switches

Sept. 1, 2005
Rotary-blade switches tend to find use in environments that would make other kinds of switches unreliable.

tend to find use in environments that would make other kinds of switches unreliable. Examples include mining and earthmoving equipment, as well as military gear deployed in deserts.

These switches are particularly rugged thanks to their use of double-wiping contact blades on both sides of a terminal. The contact cleans itself with every closure so switch makers can guarantee 10-m resistance over the life of the switch. This design is also virtually shockproof.

are composed of modules stacked together on a steel shaft connected to the front knob. The knob turns the shaft to select various switch configurations. A detent module gives tactile feedback as the knob moves to each position on the dial. It does so through use of a star wheel and springloaded ball bearings.

Switch modules, called decks, each hold a phenolic molding that contains electrical contacts. Wiper blades mounted on the steel shaft connect to these terminals as the user turns the knob. Make-before-break (shorting) contacts allow sequential connections to the same switching deck, while spring-return to normal (vertical) is a standard feature on many of these devices.

Finally, a stop-plate assembly contains stop screws inserted in the path of a stop arm. These limit the number and location of switch positions.

These switches tend to be heavy duty devices spanning typical ranges of 5 to 30 A at 600 V. Optional features often include waterproof mounts, gear-driven operation, push-to-turn handles, and key operation.

Electroswitch Corp. ( provided information for this article.

About the Author

Leland Teschler

Lee Teschler served as Editor-in-Chief of Machine Design until 2014. He holds a B.S. Engineering from the University of Michigan; a B.S. Electrical Engineering from the University of Michigan; and an MBA from Cleveland State University. Prior to joining Penton, Lee worked as a Communications design engineer for the U.S. Government.

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