Dry Contacts vs. Wet Contacts

What's a VFC?

I hate this terminology! But, assuming that you really have to use it:

We are addressing switch or relay connections.

"Dry contact" and "Volt-free Contact" are the same thing. They refer to a switch (or contact) that is essentially floating as provided on the equipment, so that the user can connect it between any two nodes of his/her network as he prefers. That means that it is only useful if both terminals of the switch are brought to the user interface.

"Wet" contact means that one terminal of the switch (or contact) is connected to a signal (typically a Voltage or current source) internally to the equipment. So the output of the switch is either O/C or connected to the signal source.

This thread should be closed...the answer has been given clearly and with no doubt. If it is ok Physicist I would your approval to copy this and use it in the boiler class that I teach at our local college.

I think we should have a way to end a thread when the best answer has been given

I believe VFD or VSD was the intended equipment in the question.

Mike

Of course you can use it.

N.B. If I were teaching the course (I'm more into measurements, so it won't happen) I would want to ensure that the victims (er.. I mean students) understood where the terms might be used with different meanings - which is why I added the other postings.

P.S. In case your students enjoy the ridiculous: a switched output described as wet (=powered) and wetted (=contact oxide bridged by the action of a preliminary current)...

P.S.2. and don't you just love the common usage "VSD drives"

Thanks.

P.S. my victims will like this too

P.S.2. "drives" VSD or VFD or otherwise miss used drive me nuts. I agree.

rag kumar; i think of a wet contact as a mercury wetted contact that keeps renewing it self for many operations, open or closed. a dry contact wears out. perry

That's perfectly reasonable in some contexts, though personally I would always include the full string for "mercury wetted" contact in a first reference, and thereafter usually refer to it as wetted (rather than "wet"). However, this meaning does not appear appropriate in the context of the enquiry, as it bears no relation to the Voltage-Free Contact. [N.B. given the choice (rarely possible), I would prefer to use the terms such as "switched output" or "energised" for the so-called "wet" relay].

Unfortunately, "wetted contact" (name not including mercury) has yet another meaning. A wet circuit is a circuit in which which current is specifically forced through the contact in order to punch through oxide layers and thus ensure that a decent contact is made; the contact in such circuits is frequently described as "wetted". [The current typically needs to be somewhat more than 10-mA].

Perhaps this will partly explain why I mentioned how much I dislike the dry/wet terminology when applied to electrical contacting?

Guys,

I notice today that people are replying from their strengths and starting to abuse other correspondents. This is becoming across a wide variety of threads. I am saddened.

It makes me want to stop reading and joining in.

As an electronics engineer with interests in mechanical, electrical and civil engineering, with additional topics such as Astronomy I am one of those that did not understand the Wet/Dry issues just discussed.

I am afraid that in my 55 years experience the only wetted contacts were, to me, the mercury wetted type.

Mea Culpa!

I have learned something else today.

Sleepy

Unfortunately, you have to expect the odd lapse of discipline if you run a forum that allows unchecked and unidentified participants. But this level of openness also has advantages, so we need to "take the rough with the smooth" It seems the moderators have recognised the problem on this occasion and removed the offending items - I think they have got it about right, because only the most flagrant breaches are usually cut out.

On the subject of the different types of wet and wetted contacts:
I don't think you were missing anything that you might have needed to know in advance, because the context would have been sufficient to warn you that it did not mean mercury, and you would have checked.
Even so, although it has not yet caused me a problem, I would always have chosen alternative terminology if I ever needed to write about this stuff - and personally, I can only wish that the water analogy had not been poured this far.
N.B. I believe that contact oxidation was at one time a major problem for suppliers of electro-mechanical relays to the telecomms industry - a brief consultancy was where I first heard of using so-called wetting to overcome that one.

Physicist,

Thanks for that, I do get concerned when people "yell" at each other though this sort of medium. Mud tends to stick whilst we should be helping those who do not undersatnd some concept, issue, discipline whilst tryinmg to pesuade some others that they should do some of their own research first!

On the wetted contacts your last paragraph sums up my experience - or lack of it!!

Thanks very much,

Sleepy