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Measuring Ac signal phase reversing

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ismu

ismu

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I have attached one picture , i want to measure ac 250 volt through MCU , and am scaled to 0-5v range without any isolation .
i could measure very currectly without any error . But when we reverse the phase and neutral from its normal position as per the picture ,the phase will directly come to MCU and if we touch on MCU pin,we got Shock [But working fine]. But if we connect as per the picture there no problem when we toch on mcu pin.
So have any idea to remove this problem[without using any opto] or Can MCU dettect phase is reversed or not?
 

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Phase reversal is dificult to detect in this case. One thing that can be done if you add one more wire i.e. Earth. When you have earth connection you can easily detect if the connection is reversed for the phase and neutral.
 
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    ismu

    ismu

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Good
that i know ,any other case to remove shock without earth wire?
 

To be 100% safe I suggest to put device in housing out of plastic and isolate user from parts that can be under voltage in any case.
I wondering that the case when PE wire is broken in any place could not show that phase is reverted.
 
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    ismu

    ismu

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Preventing shock means that every surface a user might tough is either earthed, or properly insulated from all circuitry connected to the line. It's hard to give recommendations without knowing what the device looks like and what kind of interface it has.
 
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