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wetted contacts?

Discussion in 'Electrical Engineering' started by Spider, Sep 20, 2003.

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  1. Spider

    Spider Guest

    Hi all,

    I'm familiar with the term 'Dry' contact, i.e. one with no voltage on it or
    referred to as 'Clean', however I was told that the term 'Wetted' was
    applied to contacts with a voltage applied to them which has the effect of
    keeping the contact 'clean'.

    Can any of the learned colleagues shed any light on this


  2. Spider

    Spider Guest


    Thanks for the reply, the problem was to do with intruder alarm inertia
    switches that the internals stay in the exact same position for years, and
    therefore over time pit and so cause high resistances, a colleague mentioned
    that older equipment with higher detection loop voltages kept the device
    contacts clean by the application of this voltage, I at first thought the
    same as you, but the contacts are hermetically sealed and contain mercury or
    other conductive liquid.

  3. Mark Empson

    Mark Empson Guest

    This is probably refierring to the wetting current of the contacts.
    The problem with contacts slowly oxidising and going electrically open over
    a period of time when they are physically closed can be prevented by
    ensuring that there is sufficient current flowing through them. This current
    is known as the wetting current. - the current that will ensure that the
    contacts will not go open circuit due to surface degradation.
    The wetting current is dependant on the contact material, surface area,
    pressure and voltage. Gold provides one of the best contact materials for
    low current, low voltage applications. Silver Cad Oxide contacts are good
    for switching high voltage high current, but have a high wetting current and
    cause problems in situations where they are maintained in a closed state for
    extended periods of time with low voltage low current circuits.

    Best regards,
    Mark Empson.
  4. Spider

    Spider Guest

    Many thanks for the informative replies


  5. rjb

    rjb Guest

    Wetted just means with voltage on them. No cleaning, no mercury.
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