Re: Relays and Contactors

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Mddeming-at-aol-dot-com>

In a message dated 2/5/02 10:58:01 AM Eastern Standard Time, tesla-at-pupman-dot-com
writes:


>
> During the past I've seen arcing from connections being pulled apart, or any
> situation interrupting high currents.
> The planned current load will be 240vac -at- ~20amps continuous duty. What would
> prevent excessive arcing when the contacts open under full load? Is there a
> difference between relays and contactors in this respect? 
>
> I will be using Variacs to ramp up power and back down again but if the
> deadman's switch opens at full power....??
>
> Rick W.
> Salt Lake City



Hi Rick,
         FWIW, I use a contactor rated at 2-3 times the load in my power
cabinet. As to the etymology of the words: I believe that the term "relay" came
out of the communications industry, where "information" was going through the
contacts, while "contactor" came out of the electrical industry, where the
stuff going through the contacts is pure power. As such, contactors are often
designed with a spring loading to minimize the time the contacts are within
arcing distance of each other on opening. Operationally they are the same.
Think of a contactor as "a fast-opening relay on steroids".

Matt D.
G3-1085
(Oops! perhaps "steroid" is a bad word to use around Salt Lake City this
month)  ;-))