No i ment 12v gnd, add a capacitor between this gnd to chassy gnd, ie mains earth.I'm trying to use a processor very close to a very noisy frequency inverter which is why I'm trying lots of different things to get it to work, I'm kind of encasing it in a metal box inside a metal box to try to minimise noise
No i ment 12v gnd,
That is fine. As long as the 12V supply is somewhere along the line isolated from the mains then no harm will come. It would be unusual for it not to be isolated.If you think about it, when ever you make a measurement with an oscilloscope the ground signal of your probe is connected to the mains earth. So when you clip the ground of the probe to the ground of your circuit you are doing exactly the same thing.
But then big brother stepped in and said 'hey, we know what's better for you, and your safety'.