wetted contacts?

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
Regards
Ian
Reply to
Spider
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in article bkhufe$7q0$ snipped-for-privacy@news8.svr.pol.co.uk, Spider at snipped-for-privacy@Hotmail.com wrote on 9/20/03 9:15 AM:
This may be refering to mercury wetted contacts.
Bill
Reply to
Repeating Decimal
Bill,
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.
Ian
snipped-for-privacy@Hotmail.com
Reply to
Spider
Hello 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.
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Reply to
Mark Empson
Ian, you've hit on one meaning of the term 'Wetted Contacts'. The other, which is the one I am more familiar with involves the contacts being wetted with mercury partially to reduce resistance but mostly to reduce contact bounce.
Harry C.
Reply to
Harry Conover

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