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#5196 - 11/07/01 08:58 PM Dry Contacts  
Frank Cinker  Offline
Member
Joined: Jul 2001
Posts: 311
Pennsylvania
I've often heard fire alarm technicians use the term "dry contacts". At the risk of posting a dumb question I ask what are dry contacts.


Work Gear for Electricians and the Trades

#5197 - 11/07/01 09:09 PM Re: Dry Contacts  
sparky66wv  Offline
Member
Joined: Nov 2000
Posts: 2,236
West Virginia
Didn't use saline before you put them in your eyes?

Sorry, couldn't resist...

Dunno... An askeral (grease, noalox) to help prevent arcing?

Got me...


-Virgil
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#5198 - 11/07/01 09:36 PM Re: Dry Contacts  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,311
Frank,
they are a set of N.O. or N.C. contacts that are not energized, therrfor the term 'dry'

yaknow, if someone published a book of 'trade slang' i'd buy it

[Linked Image]


#5199 - 11/07/01 11:16 PM Re: Dry Contacts  
Bill Addiss  Offline
Member
Joined: Oct 2000
Posts: 3,878
NY, USA
Sparky,

Got something close;

Dictionary of Comstruction Terms

Bill


#5200 - 11/07/01 11:52 PM Re: Dry Contacts  
wolfdog  Offline
Member
Joined: Oct 2001
Posts: 135
Dallas,TX
I understood they were very low resistance contacts-like gold plated. I have run across
that requirement for alarm circuits in a/c units before. An official ruling would be helpful.


#5201 - 11/07/01 11:53 PM Re: Dry Contacts  
NJwirenut  Offline
Member
Joined: Sep 2001
Posts: 806
Bergen County, NJ
"Dry Contacts" refer to a set of electrical contacts that switch such low voltage/current that there is no "self-cleaning" effect caused by arcing/sparking during operation.

Contacts used in such applications should be made of precious metals (gold, rhodium, platinum, etc.) to ensure reliable operation, especially in a corrosive atmosphere where an insulating film might build up.


#5202 - 11/07/01 11:59 PM Re: Dry Contacts  
electure  Offline


Member
Joined: Dec 2000
Posts: 4,260
Fullerton, CA USA
Well, let's see. A mercury switch is a "wet contact", so...
A "dry contact" is the one all of us are accustomed to seeing, with contact points.
The wet contacts don't wear out like the dry ones, and unless I'm wrong (as usual), are capable of carrying higher current for their relative size.
Scott 35, are you around?


#5203 - 11/08/01 08:10 AM Re: Dry Contacts  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
I would say any set of "field contacts", such as those that are part of a pressure, or flow switch assembly that do not contain an internal power source.


#5204 - 11/08/01 09:54 AM Re: Dry Contacts  
JBD  Offline
Member
Joined: Jul 2001
Posts: 599
WI, USA
The terms dry and wetted have nothing to do with the physical construction of the contacts.

A dry contact is a contact that receives power from a source. Examples include:
Thermostats, Pushbuttons, Doorbell buttons, relay contacts, door switches, and even standard light switches.

A wetted contact is a contact that provides power to a load. Examples include:
Time clock switches, Commercial float/pressure switches, and most low voltage solid state controls.


#5205 - 11/08/01 10:28 AM Re: Dry Contacts  
electure  Offline


Member
Joined: Dec 2000
Posts: 4,260
Fullerton, CA USA
I'm missing the boat here in a big way.
Not to be sarcastic or disrespectful but:
All contacts receive power from a source.
No contact makes its own power.
All contacts supply power to a load.
The examples given by JBD could be reversed, and it would still seem to make just as much sense to me...none.
(I'm looking around the house for my dunce cap)


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