Isolation monitoring on non-earthed mains systems

I'll be working on a mains generator which uses the IT (non-earthed) system. There is an insulation monitoring system which measures the resistance between the mains supply and earth, and shut off if there is conduction.

I had not come across this sort of system until recently. Does anyone has any experience of them, and how well they work in practice?

The system uses an imposed DC voltage to measure the resistance, and I wanted to know how it will react to real-life faults, not just ideal resistors between live or neutral and earth.

As you know spectral leakage current to ground is a more common fault for EMI.

I would think an AC conduction method is better just as it is for ground moisture.

Are minor capacitive coupling leaks to be considered ? ( Live conductors-to-grounded conduit.)
Are capacitive leaks to consider between live phases ? Guessing the IT generator is AC ?

A current transformer with a very high turn count comes to mind...

Externet said:

Are minor capacitive coupling leaks to be considered ? ( Live conductors-to-grounded conduit.)
Are capacitive leaks to consider between live phases ? Guessing the IT generator is AC ?

A current transformer with a very high turn count comes to mind...

Click to expand...

The IT generator is AC, same voltage and frequency as domestic mains.

Capacitive leaks between live phases would be indistinguishable from a capacitive load, such as a power factor capacitor or a transformerless power supply, so those are not considered, but they wouldn't be with an earth leakage breaker on a grounded system.

On the system that I'll be working on, capacitive leaks, like the Y-capacitors in some appliances, are not to be considered.