Neutral CT on Shelly 3EM

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1. How to calibrate Shelly 3EM with a neutral CT?

Update the shelly 3EM device to fw 1.12, where the functionality for neutral CT is supported.

1. Lock N to phase A, don't unlock A clamp.
2. Choose to calibrate N from A
3. If callibration fails, reverse N and try again.
4. When is successful move N clamp to Neutral wire.

2. How to interpret the readings for A+B+C RMS and Neutral RMS? 

It is important to take in mind the error from the equipment.

A small difference between 0.5 A and 1A could be taken for normal.
Higher difference could mean leakage in the electrical network.