How does a mechanical switch clean itself?
It's not a cat.
Well, it may not be a cat, but I'd think "self-cleaning" simply means that normal usage is sufficient to keep the contacts nice and shiny. Gold-plated contacts have very low wetting current requirements.
If you've ever had to clean or replace a protection relay in a hi-fi amplifier or rx/tx relay in a transceiver, you know what is not "self-cleaning". Those protection relays typically have silver-plated contacts which can be switched under load if needed (unlike their gold-plated colleagues), but if the relay isn't at least halfway airtight, the contacts will slowly oxidize due to sulfur compounds in the air (like silver cutlery). Usually there is not enough current flowing over them to burn away these oxide layers, which in turn build up over time, degrading damping factor and eventually even causing intermittency. Silver-plated contacts need about two orders of magnitude more wetting current than gold-plated ones, so you might see like 20 mA vs. 0.3 mA.
(I once had the pleasure of cleaning a drum tuner with silver-plated contacts in a VEF 206. Those didn't look too good before, and the set didn't say much either. Heck, the old Grundig Satellit sets had drum tuners with gold-plated ones which commonly STILL need good cleaning to restore optimum reception.)
