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Joined: Jul 2001
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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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Joined: Nov 2000
Posts: 2,236 Likes: 1
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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 Residential/Commercial Inspector 5 Star Inspections Member IAEI
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Joined: Oct 2000
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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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Joined: Oct 2001
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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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Joined: Sep 2001
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"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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Joined: Dec 2000
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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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Joined: Mar 2001
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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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Joined: Jul 2001
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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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Joined: Dec 2000
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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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Posts: 75
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