Re: relays




John Larkin wrote:

Guy Macon <http://www.GuyMacon.com/> wrote:

Note [1]: The physics are a bit different for contactors with no
wiping compared to relays with wiping.

Contactors aren't relays?

Where does the above imply that contactors aren't relays?

Looks like I have to explain basic logic to you...

What I wrote above makes two claims:

[1] There exists an object that is a relay and has wiping contacts.

[2] There exists an object that is a contactor and lacks wiping contacts.

From those claims, it is invalid logic to conclude that the
logic of the two claims above lead to a claim that

[3] (false conclusion)
There exists no object that is a relay and a contactor.

Given your ongoing pattern of making silly mistakes and then digging
in your heels rather than admitting that you were wrong, I fully
expect you to reply that you did not come to a false conclusion in
your logic, but you have not (so far) made any error concerning
what a relay is and what a contactor is, so I am hoping that you
are still educable on that topic. Perhaps this will help:

There are no good definitions in the standards that we use to define
electrical components. Normally I would simply go to IEEE Std 100-1992
(Standard Dictionary of Electrical and Electronic Terms), but it has
multiple definitions for Relay and an inadequate definition for
Contactor.

The AIEE (which became the IEEE) had a slightly better definition:

Relay: A device by which contacts in one circuit are operated
by a change in conditions in the same circuit or in one or
more associated circuits.

Contactor: A device for repeatedly establishing and
interrupting an electric power circuit.

The Struthers-Dunn Relay Engineering book from the 1940s
gives these definitions:

Relay: An electrically controlled device that opens and
closes electrical contacts to effect the operation of other
devices in the same or another circuit.

Contactor: A magnetically-operated device, for repeatedly
establishing and interrupting an electrical power circuit.
It is usually applied to devices controlling power above 5kW,
whereas the term 'relay' is ordinarily employed below 5kW.
The terms are often used interchangeably.


In my experience, common usage is that a "Relay" is small
and usually has contacts that wipe, while a "Contactor"
(sometimes called a "Contactor Relay") is big, has a crossbar
that bridges dual contacts without wiping, usually has a
way to actuate it mechanically as well as a low current
signal contact (often used to drive an indicator lamp), and
at times contains a thermal overcurrent protection device on
each contact. That being said, I certainly wouldn't correct
someone who uses the two terms interchangeably. That's why
I added the qualifiers in what I wrote above.

And, of course, from the context I am assuming electrical
relays and not pneumatic or hydraulic relays and I am
ignoring such things as motor-driven contactors or ballistic
contactors...

--
Guy Macon
<http://www.GuyMacon.com/>

.

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