Yes you're right - IT is the earthing arrangement of the network, as opposed to TN most common in UK. I only mention 'delta three-phase' as that's what Tesla call it in the Wall Connector user manual and if you're on the IT-net here you wire up the Wall Connector according to that scheme using L1, L2 and N even though there is no N - like I say, weird! I'm fairly sure the distribution transformer secondaries are not actually delta-connected here - they are wye with ~132 L-N, 230 L-L and the neutral point is left isolated, only the three phase wires in the local network to consumers. So effectively there is no single-phase here - as a minimum you use two of the three phases for a 'single-phase' 230 V supply, but all houses have all three phases.
In the Wall connector setup on the IT network you must disable the ground assurance monitoring. This is monitoring for low earth fault loop impedance and depends on an earthed neutral, so it will freak out and alarm on the IT network. I guess most likely a similar check is preventing foreign UMCs from working in Norway and it is disabled in Norwegian UMCs. My Norwegian UMC will work anywhere, but technically is less safe as it is not doing this ground monitoring.
