Hi Chitrakar,

I worked with one of the leading Indian meter manufacturing company as R&D manager [ I wouldn't like to name here ]. In my single phase and 3 phase multifunction power and energy meters we used MSP430 family 16 bit micro controllers. Here the voltages applied were AC 600V [ Phase to neutral ] and currents 5A/1A.

The current inputs were isolated using CT, but voltage inputs were never isolated. Neutral was connected to GND of meter supply and
Phase inputs were connected to resistor divider with this divider network output directly connected to microcontroller analog input pin with clipper clapper diodes to protect over / under voltage inputs. We used BAT54S Schottky diodes.

This resistor divider reduced voltage & also level shifted voltage signal.

   
          VCC
           |___
           |   |
          5k   _
           |  /_\
           |   |
-----2M----------- Microcontroller ADC input
           |   |
           |   _
          5k  / \
           |   -
           |___|
          GND

These products required PC communication using modbus over RS485. We used Analog devices ADM2483 isolated transceivers. In some products we also used 6N137 opto isolators + 75176 for same purpose. Both ways it always worked absolutely well.

With resistor dividers + adequate diode protection your micro is safe.

As someone already mentioned in this thread the problem is only when you connect a PC or some other such thing thats connected to mains thats why you need isolation in communication signals.

Also the above method is not safe if this board comes in contact with humans. There is risk of electric shock. Take adequate measures in enclosure design.

Regards,
Prahlad Purohit