Red_Micro,
1. do you expect any extreme fault currents in the primary conductor? If so, R34 could be damaged and without a burden resistor a much higher voltage could be applied to the circuit. Is R34 sized for a reasonable short term overload?
2. will the primary conductor have a high AC voltage on it? There will be some capacitive coupling between the conductor and the secondary winding that is probably insignificant. Have you calculated or measured what the leakage current might be?
3. the net marked "Vcc/2" actually has a reference voltage on it, no? I'm assuming that ADC_in2 is sampled to read the DC offset of that net to determine the 0 V point for the ADC_in samples.
4. the 100R & 0.01uF RC filters have corner frequencies of 159 KHz. This seems too high to do much good. What is your samping rate? Is it synchronous to the line frequency?
5. C18 and R34 form an RC filter with a corner frequency of 1.59 MHz. This also seems high.
1. Yes, I'm expecting some short term extreme fault (no frequent though). I'm sizing R34 1W-2W maybe. I'm still thinking of adding some diode.
2. I haven't calculated such leakage current between primary and secondary. I feel tempted to not put the coupling cap or at least leave the footprint on the PCB.
3. Vcc/2 is the voltage reference coming from the LM4041 IC. It's for the DC offset, and it also goes to an ADC input. I'm thinking of removing the buffer since the reference IC may handle that load well.
4. I haven't defined my sample frequency. Not synchronous with the line frequency though. As the signal is 60 Hz, the sampling freq probably won't be high.
5. You're right. Increasing C18 to 100nF would be better.