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I would like to ask about three kinds of electrical contacts: dry, wet and free voltage. What is the difference between them?

Adban
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    It would be very helpful if you provided links to example of these terms in use in the way you are querying them. I could answer as asked but it may not explain what you want. | Dry - not mercury wetted OR does not need minimum current to switch well. | Wet - mercury coated or must operate with a minimum operating current. | free voltage is probably "voltage free" Refs please. – Russell McMahon Jan 10 '12 at 14:34
  • Take a look here: http://en.wikipedia.org/wiki/Dry_contact – m.Alin Jan 10 '12 at 20:45
  • Or here - which is even a better explanation: http://www.leachintl2.com/english/english2/vol6/properties/how4.htm – qdot Jan 14 '12 at 02:35

2 Answers2

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A dry-contact or voltage-free is one where the controlling electronics have no direct contact at all typically the switch side of a relay.

The idea is to be the perfect hand-over point between two electronic systems where neither party has to know about the others electronics to be able to interact.

back_ache
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I haven't heard all of those terms in use -- they may be part of a local slang. Alas, the main problem with contacts in connectors and relays is that the metal coatings/platings on the mated contact pair differ depending on the application and current.

The main choice is gold vs. silver. If you have low current (up to dozens of mA) signal connections, you need gold plating/flash. If you have high current connections, the gold flash will be eroded if the connection is made or broken under load. Such connections are from that point onwards unsuitable for low current use! The ideal high-current plating material is silver.

Tin contact plating is not something I'd really like to use in an application designed for longevity.

Kuba hasn't forgotten Monica
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