Dry Contact: Definition, Examples, & More

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Discussion Overview

The discussion revolves around the concept of "dry contact" in electrical circuits, exploring its definition, examples, and distinctions from "wet contact." Participants inquire about the implications of dry contact in various applications, including relays and transistor switches.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about the definition of dry contact, questioning if it refers to a comparison with wet contact, such as in mercury switches versus regular relays.
  • Another participant clarifies that dry contact typically means the relay does not provide a source of voltage or current, and that external equipment must supply the necessary voltage/current to sense the relay's state.
  • A different participant describes their use of dry contacts as part of an interrupting circuit or relay output, providing an example involving a resistance furnace and solid state relay.
  • One participant defines wet contact as mercury wetted contacts and suggests that dry contact can mean either no mercury or a small current controlling a larger contactor, depending on the context.

Areas of Agreement / Disagreement

Participants present varying interpretations of dry contact, with some agreeing on its definition related to the absence of a voltage source, while others provide different contextual uses. The discussion remains unresolved regarding the precise definitions and applications of dry versus wet contacts.

Contextual Notes

There are limitations in the discussion regarding the assumptions about the definitions of dry and wet contacts, as well as the specific contexts in which these terms are applied. Participants do not fully resolve the distinctions or provide comprehensive examples.

likephysics
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I am confused about dry contact. Does it mean dry contact vs wet contact as in mercury switch vs regular relay.
Any circuit examples.
Are transistor switches also referred to as dry contacts.
Is a NPN transistor with open collector output also referred to as dry contact?
 
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Almost always means that the relay itself does not provide a source of voltage or current.
The contacts are simply two conductors coming into contact.

The equipment that is monitoring the dry contact must provide voltage/current to sense the state of the relay.
 
I always used "dry contacts" basically as an interrupting circuit or relay output;

For example with a resistance furnace power always goes through a dry contact before the solid state relay. the dry contact functions as the over temp/alarm/permissive signal and the solid state as the control.

Many industrial instruments have "dry contact" relays in them which can be used to start/stop a completely separate circuit.
 
Wet contact, to me, means mercury wetted contacts which are literally wet with mercury.

Dry contact either means no mercury or a little current that controls a larger contactor, depending on the context of its use.
 

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