Using built-in gain on ADC vs different current-transformer?
Is it correct to assume that the one with the "larger" range will give more precision? If so, is there a way to know where it's a meaningful amount of additional precision?


To calculate how much precision you get using different CTs and different ADC configurations, you need to know how much the CT voltage varies per amp and what proportion of the full-scale input range that corresponds to for your ADC

If you use a 50A, 1.0Vac CT, the peak voltage will be sqrt(2) * 1.0Vac = +/- 1.41Vdc. Note that you will need to map this to the range 0 .. 2.82Vdc (or similar) since the ADS1015 doesn't allow negative input voltages (check the absolute max ratings in the datasheet: no more than -0.3V on any input)

So your CT maps 0 .. 50A to 0 .. +/- 1.41Vdc, varying by 28mVdc per amp

Looking at the datasheet for the ADS1015, there's a table on page 10 which shows the full-scale voltage ranges for different gain settings. A gain of 1 with FS of 4.096V seems most appropriate here since you need a FS value larger than the 2.8V you want to read. Note that you won't be able to read voltages higher than the 3.3V provided by your RPi with any gain setting!

I'm not particularly familiar with the ADS1015 but I understand the reason those FS ranges are given as plus/minus 4.096V is that you can use it in differential mode and if the 'negative' (or inverting) side of the input is higher than the positive (non-inverting) side then your reading is considered to be negative. Both sides of the input still have to be positive, however - don't forget about the absolute maximum ratings of -0.3V to VDD+0.3V!

Anyway, if you have a measurement range of -4.096V to +4.096V and a resolution of 4096 (12bit) then you get a voltage resolution of 2 x 4.096V / 4096 = 2mV

So if the CT output voltage varies by 28mVdc per amp, and we can detect changes of 2mV with our ADC, then we can detect changes of 71mA to your house current draw (28/2 = 14 steps per amp, 1/14 = 0.071A). I suspect that's more than enough accuracy for your domestic purposes.

What if you use the 50A, 0.330Vac version?


Peak DC voltage is +/- 0.467Vdc
Gain setting should be 4, giving a FS value of +/- 1.024Vdc
ADC resolution is 0.5mVdc
CT varies by 9.3mVdc per amp
Minimum detectable current change is 54mA


So you actually get better precision using the 0.330Vac version and a higher ADC gain, however you will be more susceptible to noise. Will the noise be significant? I have no idea - you can only answer that empirically. However, you can be sure that the 1.0V version will be less noisy, so if a resolution of 0.071A is precise enough then the 1.0V option may be best