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#5196 - 11/07/01 04:58 PM Dry Contacts
Frank Cinker Offline
Member
Registered: 07/29/01
Posts: 311
Loc: 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.
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#5197 - 11/07/01 05:09 PM Re: Dry Contacts
sparky66wv Offline
Member
Registered: 11/17/00
Posts: 2232
Loc: 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...
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#5198 - 11/07/01 05:36 PM Re: Dry Contacts
sparky Offline
Member
Registered: 10/18/00
Posts: 5303
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

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#5199 - 11/07/01 07:16 PM Re: Dry Contacts
Bill Addiss Offline
Member
Registered: 10/07/00
Posts: 3875
Loc: NY, USA
Sparky,

Got something close;

Dictionary of Comstruction Terms

Bill
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#5200 - 11/07/01 07:52 PM Re: Dry Contacts
wolfdog Offline
Member
Registered: 10/24/01
Posts: 135
Loc: 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.
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#5201 - 11/07/01 07:53 PM Re: Dry Contacts
NJwirenut Offline
Member
Registered: 09/15/01
Posts: 806
Loc: 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.
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#5202 - 11/07/01 07:59 PM Re: Dry Contacts
electure Offline


Member
Registered: 12/24/00
Posts: 4259
Loc: 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?
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#5203 - 11/08/01 04:10 AM Re: Dry Contacts
Redsy Offline
Member
Registered: 03/28/01
Posts: 2056
Loc: 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.
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#5204 - 11/08/01 05:54 AM Re: Dry Contacts
JBD Offline
Member
Registered: 07/12/01
Posts: 599
Loc: 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.
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#5205 - 11/08/01 06:28 AM Re: Dry Contacts
electure Offline


Member
Registered: 12/24/00
Posts: 4259
Loc: 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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