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

[Steve]

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 ?

 

[Steve]

I now see that the C&K data sheet also says the Q material is also
rated to 5 A at 120 V AC or 28 V DC. The Digikey catalog says that is
not for the 7000 series switches - only for the E series.

 

[Rich Grise]

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 ?

There's a pretty good explanation of "dry switching" here:
http://www.planetanalog.com/columns/mixed_signals/showArticle.jhtml?articleID=202405362
(mind the wrap)

Hope This Helps!
Rich