What exactly are dry contacts

[JDBrown]

Just because mercury is a liquid at room temp, does that mean it is wet?

Uh, yeah? What else would wet mean?

1. moistened, covered, or soaked with water or some other liquid: wet hands.
2. in a liquid form or state: wet paint.
3. characterized by the presence or use of water or other liquid.

 

[kwired]

Uh, yeah? What else would wet mean?

I've never had "wet hands" with mercury being the "wet" part.

I used to play with mercury as a kid out of thermometers or old HVAC thermostats, it never had a tendency to act much like water does, and was not absorbed by many items like water does either.

Oh yeah, because I played with mercury and even lead like I did, I also should have been really ill or even died years ago.:roll:

 

[hbiss]

What do you want to call mercury relay contacts? I want to call them wet. These exist in both a big pool of mercury, or so called mercury wetted contacts. Both exhibit no contact bounce.

Yes, mercury wetted contacts. That is different from "wet contacts".

Does that mean that they are "dry" only until they are installed?

Well not exactly. It means that the contacts are available for field configuration any way the installer wants within the capability of the switching device. Wet contacts are pre-configured to provide some kind of voltage or signal to an output and cannot be changed.

-Hal

 

[GoldDigger]

... some kind of voltage ...

Including just ground.

 

[hbiss]

Keep in mind also that this (dry contact/wet contact) terminology is usually only used in the LV fields such as security, fire systems, control, etc. That may be why it's not familiar to everyone. The electrical and electronic trades just refer to contacts as contacts.

-Hal

 

[hurk27]

I have always took the term to mean an isolated set of contacts with no reference to any other part of the circuit to which they may be a part of, extra aux contacts on the side of many motor starters are often referred as dry contacts as well as the aux contacts in disconnects that we use to tell the PLC what state the disconnect is in,
in most cases these aux contacts are used to signal another system thus they do not have any electrical reference to the device they may be monitoring, drives use dry contacts in disconnects at the motor to know to shut down if someone goes to switch off the disconnect.

 

[don_resqcapt19]

Keep in mind also that this (dry contact/wet contact) terminology is usually only used in the LV fields such as security, fire systems, control, etc. That may be why it's not familiar to everyone. The electrical and electronic trades just refer to contacts as contacts.

-Hal

It is commonly used in the electrical trade, at least around here, for industrial control systems. Often these are 120 volt systems.

 

[Besoeker]

It is commonly used in the electrical trade, at least around here, for industrial control systems. Often these are 120 volt systems.

Yes. Here too. But more often called volt free.

 

[ggunn]

Uh, yeah? What else would wet mean?Originally Posted by http://dictionary.reference.com

moistened, covered, or soaked with water or some other liquid: wet hands.
in a liquid form or state: wet paint.
characterized by the presence or use of water or other liquid.

I don't think that mercury can wet anything except some metals such as silver, and even then it's forming an amalgam. It pretty much keeps to itself.

 

[Besoeker]

I don't think that mercury can wet anything except some metals such as silver, and even then it's forming an amalgam. It pretty much keeps to itself.

We make mercury wetted switches.

 

[JDBrown]

Just because mercury is a liquid at room temp, does that mean it is wet?

Uh, yeah? What else would wet mean?

1. moistened, covered, or soaked with water or some other liquid: wet hands.
2. in a liquid form or state: wet paint.
3. characterized by the presence or use of water or other liquid.

I've never had "wet hands" with mercury being the "wet" part.

I used to play with mercury as a kid out of thermometers or old HVAC thermostats, it never had a tendency to act much like water does, and was not absorbed by many items like water does either.

Oh yeah, because I played with mercury and even lead like I did, I also should have been really ill or even died years ago.:roll:

I don't think that mercury can wet anything except some metals such as silver, and even then it's forming an amalgam. It pretty much keeps to itself.

Sorry, guys; I was just foolin' around. Didn't mean to be taken seriously. :ashamed1: Perhaps I should have added a smiley or an eye roll to my earlier post.

In all honesty, I've found this thread very informative. I, too, have often wondered what exactly was meant by "dry contacts." So thanks, everybody.

 

[ggunn]

Sorry, guys; I was just foolin' around. Didn't mean to be taken seriously. :ashamed1: Perhaps I should have added a smiley or an eye roll to my earlier post.

In all honesty, I've found this thread very informative. I, too, have often wondered what exactly was meant by "dry contacts." So thanks, everybody.

Particle man

Is he a dot, or is he a speck?
When he's underwater does he get wet?
Or does the water get him instead?
Nobody knows, Particle man

 

[kwired]

Sorry, guys; I was just foolin' around. Didn't mean to be taken seriously. :ashamed1: Perhaps I should have added a smiley or an eye roll to my earlier post.

In all honesty, I've found this thread very informative. I, too, have often wondered what exactly was meant by "dry contacts." So thanks, everybody.

I honestly don't know what a dry contact is, or if there is a specific definition for the industry. As you can see the many opinions and variations mentioned here kind of support that. A couple things that maybe one doesn't always think of have come up as possibilities though, and yes this has been a pretty informative topic.

So far my definition of a dry contact is a true mechanically operated make/break switching device that has no internal power source.

I think I somehow need to modify this definition though, as I don't see a mercury switch as a dry contact yet it would still qualify in my definition as it is still mechanically operated, maybe somehow throw in continuity through switch is via linear pressure action on the contact points?