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Switch contact material rating - use 120 V AC rated with low DC ?

Comparing switches with different contact materials and their subsequent ratings.

One with copper alloy contacts and terminals with gold plate over nickel plate is rated at 0.4 VA max at 20 V AC or DC. C&K 7101K2CBE

The same switch with its end contacts of coin silver, silver plated and its center contact and all terminals copper alloy, silver plated has a 5 A at 120 V AC rating. No DC rating given. C&K 7101K2CQE

What happens if the second switch that has no DC rating is used with DC ? Does some kind of electrolysis happen with long term usage due to passign current in only one direction ? Why does it not have a DC rating ?

Would it be ok to use the second switch that has no specified DC rating with a DC signal of 10 V max if used with les than 1 mA ?

Reply to
Steve
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Reply to
Steve

When breaking inductive circuits with a DC supply (like a relay) there will be a spark generated that burns the contact material. Some switches have very small opening of the contacts when off, and the spark may not go out for some time on DC. On AC, the reversal of the voltage gives the spark time to de-ionize every 8 ms. This has nothing to do with continuous operation with the contacts closed, but os all about breaking the circuit while current is flowing.

Yes, it is unlikely that this kind of spark damage would occur on such low voltage and current. But, a silver contact may tarnish when left off for a long time, and may fail to "close", ie. break through the oxide, the first time it is operated. that may, or may not, be a big concern in your project. That is the advantage of the gold contacts, they can be left open for yests, and work the first time they are activated.

Jon

Reply to
Jon Elson

There's a pretty good explanation of "dry switching" here:

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Hope This Helps! Rich

Reply to
Rich Grise

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