Right now, i'm just concentrating on building Energymeter.
Two Options:
a) Analog ADE775X readymade chips b) 8051 micro. based
I choose second option. i.e. 8051 based.

Approach:
1) 260V, 40A max. assumed for residential, f= 50 Hz.
2) Using CT PT, step down.
After CT, use small burden resistor to convert I2V.
3)Give Voltage and Current(in V form), to ADC and then to Microcontroller.

4) ADC choice:

A) If normal ADC without sample & hold is used, then we will need RMS to DC conversion.
B) With Sample hold built in ADC: we will have to calculate RMS value mathematically SQRT[Summation(square of each sample)]

5) Sample hold built in ADC seems to be best option. This methos was also suggested by another member Pralhad Purohit. He has practically implemented this. Thanx a lot to him, for his prompt help.

********* Current Task:
Search 8 bit ADC with sample hold built in and Multiplexing.
Pralhad Purohit suggested PCF8591 Philips ADC.
But it doesn't have Parallel interface and supports I2c.
I dont have hands-on experience with project, but i think ADC-Micro. interface using Parallel ports will be easy.

6) After ADC selection , draw rough schematics and also right software flowcharts for Energy Calculation.


Any more Suggestion, most welcome.

regards,
Shantanu.