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#5196 11/07/01 08:58 PM
Joined: Jul 2001
Posts: 311
F
Member
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.

#5197 11/07/01 09:09 PM
Joined: Nov 2000
Posts: 2,236
Likes: 1
Member
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
#5198 11/07/01 09:36 PM
Joined: Oct 2000
Posts: 5,392
S
Member
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
Joined: Oct 2000
Posts: 4,116
Likes: 4
Member
Sparky,

Got something close;

Dictionary of Comstruction Terms

Bill


Bill
#5200 11/07/01 11:52 PM
Joined: Oct 2001
Posts: 135
W
Member
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
Joined: Sep 2001
Posts: 806
N
Member
"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
Joined: Dec 2000
Posts: 4,294
Member
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
Joined: Mar 2001
Posts: 2,056
R
Member
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
Joined: Jul 2001
Posts: 599
J
JBD Offline
Member
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
Joined: Dec 2000
Posts: 4,294
Member
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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