Contacts

Status
Not open for further replies.

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
There are actually two meaning sets that can apply, based on the context.

Context relating to general control circuits:
If I have a relay with a set of contacts that open and close when I energize and de-energize the coil, but the voltage source connected to the CONTACTS is going to come from somewhere else, those are considered "dry" contacts: there is no direct relationship to the coil circuit and the voltage going through the contacts. The other term for those, used in other countries, is "volts free contacts" meaning that in and of themselves, there is no voltage present on either side of those contacts until I connect them to something.

Whenever you make YOUR connection to a "dry" contact, you have "wetted" it and it is no longer a dry contact. But also if a relay has contacts that are ALWAYS connected to the same circuit as whatever is controlling it, then they are called "wet" contacts too; there is voltage on one side whenever there is voltage to the coil (or whatever is controlling the contact status). A good example of that is when a piece of equipment uses a triac as an output to signal some action. The power through that triac is what is being used to activate it, so that triac is "wet" and whatever you connect it to is then also connected to the control system behind it.

The other context has to do with old mercury relays and contactors. "Wet" contacts refers to contacts where the mercury is closing the gap between the contacts and allowing current to flow, "Dry" is when the mercury bulb is tilted to where the mercury flows away from the contacts and stops the current flow.
 
Status
Not open for further replies.
Top