How do isolation transformers affect the leakage current through protective earth in a system?
Scenario 1: Mains is directly connected to circuit. Metal enclosure has a protective earth connection to building earth. Current passing through earth conductor = I1.
Scenario 2: Line and neutral from mains are isolated from circuitry via an isolation transformer. Earth connection from enclosure to building earth remains as earlier. Current through earth conductor = I2.
I2 < I1. Is this right? Why is this? The explanation I was given was that its a simple matter of KCL. The current leaving the isolation transformer's secondary line has to return(node current equation) via the secondary neutral and hence the leakage current is lesser(in ideal cases 0).
On the other hand, if the system is powered directly by the mains, the current has the option of returning via the earth wire or the neutral wire as they have a galvanic connection at the mains end.
Firstly, is this right? If it is, then my problem with this explanation is this:
I understand that the leakage current arises because of the coupling between the circuitry and the earth connection, in this case the metal enclosure(which has a earth conductor to the building earth). Now this coupling should solely be decided by the dielectric properties of the material(s) that is separating the circuitry from the enclosure(earth). How will an isolation transformer affect this coupling(and hence the leakage current)? All the isolation transformer can do is to block out common mode noise on the primary to the secondary. So will I1 - I2 = common mode noise? Or am I oversimplifying this?
This is a conceptual question and I'm just trying to understand the basics here.