I'm in the process of designing a actuator lift for the drinks cabinet and I want to use a key switch to stop the kids getting in. The only ones I could find are rated 220v 1A. The actuator is 12v 3A. I did physics so I know the power is 36W vs 220W but I did not take the electronics module and just need to know if this is safe.
The voltage and current ratings of a switch shouldn't be equated to power. Instead, both are separate limits to what the switch is rated to handle.
Exceeding the max voltage (even without current flow) may result in internal arcing and/or short circuits. Exceeding the max current (even at a low voltage) may result in the switch conductors getting hot and melting, and perhaps welding together.
So, what you need is a key switch that can handle (at least) 3A, and also (at least) 12V.
When looking for a DC-rated component, there is another complexity: DC is more difficult to switch than AC, so the switch may have a much lower rating for DC. When you're looking at datasheets make sure that it is rated for 3A DC, not just 3A AC.