Time to plan to interface to the Arduino. The constraint is that the inputs can only be 0-5 volts. So no negative voltages.
Measuring the Line Voltage
I am using a 9VAC 1.5A wall wart to step down the voltage. To shift voltage into a 0-5 range, I used the following circuit. All I have is a digital multi-meter that measures true RMS. Open circuit measured came in at 10.5 Vrms. I assume it is sinusoidal so the peak-to-peak voltage is
The plan was to shift that into a 2.5Vp-p centered around 2.5V which will give me the required 0-5V.
A 2.5 voltage reference zener diode was used to shift the voltage up 2.5 volts. The potentiometer was used to tweak the RMS voltage to
Current measurement followed similar approach. The current transformer with a resistor in placed across the terminals produces a voltage proportional to the current. The spec sheet for the CR8459-2000-N states that the voltage is defined as
where for this CT is 2011.
It would be difficult to test this in the panel installation so max current, I, at 7.2 amps for the bench. I will need to debug stuff and will change the current to 100A when I stuff it in the panel. Note I need to do this circuit twice since I have 2 100 Amp measuring points. So solving the formula for R and setting I =7.2 and V=7.2 and using the given we get
The diagram below shows how the current measurement was interfaced. Again the potentiometer was used to tweak the RMS voltage to
The R or potentiometer value will change to value of when I permanently mount the current transformer to reflect a higher current range.