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Dry Contacts #5196 11/07/01 08:58 PM
Joined: Jul 2001
Posts: 311
F
Frank Cinker Offline OP
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.

Work Gear for Electricians and the Trades
Re: Dry Contacts #5197 11/07/01 09:09 PM
Joined: Nov 2000
Posts: 2,236
sparky66wv Offline
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
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Re: Dry Contacts #5198 11/07/01 09:36 PM
Joined: Oct 2000
Posts: 5,389
S
sparky Offline
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

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Re: Dry Contacts #5199 11/07/01 11:16 PM
Joined: Oct 2000
Posts: 3,961
Bill Addiss Offline
Member
Sparky,

Got something close;

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Bill


Bill
Re: Dry Contacts #5200 11/07/01 11:52 PM
Joined: Oct 2001
Posts: 135
W
wolfdog Offline
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.

Re: Dry Contacts #5201 11/07/01 11:53 PM
Joined: Sep 2001
Posts: 806
N
NJwirenut Offline
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.

Re: Dry Contacts #5202 11/07/01 11:59 PM
Joined: Dec 2000
Posts: 4,283
electure Offline
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?

Re: Dry Contacts #5203 11/08/01 08:10 AM
Joined: Mar 2001
Posts: 2,056
R
Redsy Offline
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.

Re: Dry Contacts #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.

Re: Dry Contacts #5205 11/08/01 10:28 AM
Joined: Dec 2000
Posts: 4,283
electure Offline
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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