Wiring Unlimited Clarification: IT and TT networks

Q&A and troubleshooting
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1

In Wiring Unlimited, when discussion floating neutral vs N-E bonded systems, it states:

With a mobile system, it is possible to create a network that is a TT network when connected to mains and at the same time become a floating IT network when the grid is disconnected and a generator or inverter is in use. This is something that is not desired and should be avoided.

Is anyone able to help me understand why having a system that switches from a TT network on shore power to floating IT network on inverter mode is not desired and should be avoided? Wiring Unlimited states that both systems are quite safe, and so what’s the risk of having it switch as shore power is connected/disconnected?

2

Because the residual current device can’t work efficiently.

3

Thanks for the reply, @Ludo!

As I understand, an RCD isn’t really necessary in an IT network, as to provide a path for current to leak you’d need to to touch both the load and neutral lines at the same time to complete the circuit, which is very unlikely. And you could still install GFCI to detect differences between load and neutral if, for instance, water completed the circuit.

But I suspect I might be misunderstanding something here…