Sensor low AC current with shunt. Question about GROUND

Using Arduino Sensors
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Hi, I have read some options about reading AC current with a Rshunt.

I have to read less than 0.1 A.

ACS712 doesnt work with so low current. But my question is more about "conecting" grounds.

As you see in the attached image, we are joining "mid point" (label 3), with and a VAC phase (label 1) in order to get a reference for label 2.

Then, with a ADC input, we will measure the voltage in label 2.

My arduino is powered by a simple 230VAC/5VDC adapter from the same 230VAC home supply.

My question is:

a) how safe is to conect arduino 5VDC and GND trought "mid point" to a VAC phase ?
b) could be Rshunt a 1/4W typical resistor ? (for 0.1A I will use a 10ohm resistor, so Watt is: 0,1W
c) does ground from 230VAC/5VDC adapter the same as label 4 or 5 ? (so it will be risky to conect that phase with mid-point (label 3)

Or there is another cheap method to measure this low current ? (I don't want the preamplified version of ACS712 shiel from sparkfun)

Thanks a lot.

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a) how safe is to conect arduino 5VDC and GND trought "mid point" to a VAC phase ?

Potentially lethal - do not do it.

c) does ground from 230VAC/5VDC adapter the same as label 4 or 5 ?

No

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What Grumpy said. There is NO cheap, safe, simple way for a hobbyist to make circuitry for measuring a current that low on a 220VAC line. Buy a professional, safety approved instrument for that.

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Thanks a lot.

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