How can you tell if Curent is Flowing?

[BuffaloJohn]

Looks good, but can I recommend a tiny change? Might want to add some back to back diodes in parallel to that CT to clamp the voltage. With a 3.3k resistor in parallel with that CT you're looking at hundreds of volts across those op-amp inputs if there's in-rush current. Probably won't be a huge problem with a resistive load that only draws an amp or two, but you had mentioned a pump and that will be a problem. Right now you're relying on the chip designer's ESD protection on each pin to save the circuit, but that will only take so many thumps before it gives up and your op-amp kicks the bucket.

Also you mention using the hot wire, but this circuit will work equally well on hot or neutral. Unless you have a ground fault the current will be identical on both wires and the circuit will function identically.

I had thought of diodes, but they aren't needed, based on breadboarding and testing. I found that the current transformer saturated at about it's maximum input current. This was found by looking at the scope with only the front end stage of the circuit, with the comparator removed. The traces were clipped, just like if saturation occured. Trust me, I pondered this quite a bit. I suspect that with the datasheet load resistor of 100 ohms max, the results would be more linear, but I didn't test that. I wasn't trying to characterize the current transformer. just experiment with it. So, in practice, the "max current" and the load resistor yielded less than 1.5V. Why? I don't know. 5mA * 3.3k should be 16.5v, but that assumes the current transformer is an ideal inductor and at 60Hz, I don't think it is even close.

There is 2.5V of headroom because of the voltage divider. I spent a lot of time with the breadboard, loads (resistive and noisy switchers), and a scope testing this because I didn't understand why I couldn't get more current passed to the secondary. I suspect it has to do with the shape of the current transformer and the field around the wire, but Maxwell's equations and EM field theory was 1974 and I don't remember any of it.

I ended up concluding that while my test loads were 10x of tha actual load, I couldn't force the circuit to get anywhere near the limits of the simple voltage shifter. Also, with the comparator, I was able to detect current at 0.01x the actual load under it's lowest operating point, so given that, diodes were not needed.

Now, it you had a more powerful current transformer, you wouldn't get away with this circuit, but again, my load was a soft start variable speed pump.