Re: contact terminology
I think we are letting our knowledge of the English language get in the way of understanding the language of our profession. In English, the terms ?dry? and ?wet? are opposites. I don?t think that there is a term in the language of electrical design and construction that is opposite to the term ?dry contact.? But even if there is, I believe it would not mean that a liquid is part of the component. Let the equipment vendors on this forum chime in, and tell me I am wrong, if they like.
My use of the term ?dry contact? carries the meaning that the circuit in which a decision is made is electrically isolated from the circuit in which a resultant action is taken. Consider a controller for an air compressor. Suppose its controller has a pressure switch in series with the motor starting coil (the ?M Coil?). As pressure gets too low, the switch changes states, allowing power to get to the M Coil, and the compressor motor begins to go roundy-roundy. That would not be a ?dry contact? arrangement.
Now change the circuit. Suppose that there is a power source that could drive current through the pressure switch, and (instead of then flowing through the M Coil) it sendis power through a relay coil. The power turns on the relay coil, and its ?a? contact (?normally open?) closes. Finally, suppose that this contact is in series with the M Coil, so that when the contact closes, the motor will start. The ?decision loop? includes the pressure switch, but the ?action loop? does not. The two loops are electrically isolated, and the isolation point is internal to the relay (i.e., the relay coil and the relay contact separate the two loops). In my view, the relay contact would fit the definition of a ?dry contact.?
Does anyone else use the term ?dry contact? in this sense?