You can also use a current sense transformer. I have one that will output 0.10v per amp. That would work on an analog pin.
Your idea to use a relay with a coil voltage of 120v is good.
You can also use a current sense transformer. I have one that will output 0.10v per amp. That would work on an analog pin.
Your idea to use a relay with a coil voltage of 120v is good.