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Re: gEDA-user: spdt, spst



Karel Kulhavy wrote:

On Wed, Jan 19, 2005 at 12:52:49PM -0600, Bert Douglas wrote:

pole = moving contact
throw = fixed contact

The terminology is old, probably going back to the time of the telegraph, perhaps 1850s. Or perhaps somewhat later at the time of introduction of electric lights in 1880s.

The first switches were exposed "knife" switches. You might see this in a frankenstein movie.

I am not sure why the moving contact is called a "pole". But I am fairly sure I understand the origin of the term "throw". To avoid arcing and shock, you would typically operate the switch by grabbing the handle and rapidly "throwing" it towards the closed position.


But there can be spdt with 2 positions (ON-ON) and with 3 positions (ON-OFF-ON)
how is this distinguished?

Cl<


These cases are not distinguished by the "pole-throw" notation.