I'm trying to understand what would happen when connecting two grounds from diffident power supplies together. A more in depth explanation of what I'm trying to accomplish is here: Connect Arduino to existing circuit with seperate power supply
One power supply is 12V and I don't know if it's floating or not in relation to earth ground. The second power supply will be 5V floating. If there's a voltage potential between the two grounds and I connect them together will there be current flow between the two grounds or will the floating 5V supply "adjust" itself to the 12V supply's ground potential?
From my understating I thought that when connecting two spots that have a different voltage potential you will get current flow between these two spots. However I'm not sure if the whole floating voltage situation changes this.