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Re: Relays and Contactors



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

Tesla list wrote:
> 
> 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".

	I would differ, mildly, (having done relay design....)
	Relays can be and are used for 'power'.
	Relays come in various speeds.
	Relays are usually faster than contactors.

	Contactors are best, i think, thought of as
		Big Thumping Relays
	Additionally, contactors are more likely to have
	'features':

		May include auxiliary (low powered) contacts,
		for control, or signalling.
		May include built in overload protection.
		(etc....)

	best
	dwp