Etack,
I am travelling atm and using my phone. It is my understanding, and you can google this, that cadmium oxide is used in the larger contacts because applications with high voltage/amps tend to ark, the cadmium oxide prevents scoring.
http://www.astm.org/Standards/B781.htm
Here is a pdf I have in my dropbox that explains why cadmium oxide is used.
http://db.tt/LlCRVjYV
I am checking into a hotel later. When I get a chance I will post what information I have.
Scott
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