I once tried a similar method in an attempt to construct an led-On indicator to show when my refrigerator was running.
I could not find a convenient place to tap into the motor/compressor wiring. So I thought of a way to detect heavy current going to the unit.
I took a transformer, and wrapped a few turns of heavy wire around it. This wire carried current to the refrigerator. (It is essential to split the twin mains lead, so that the two wires together do not neutralize each other's AC magnetic field.)
There was no galvanic contact between the transformer and mains AC.
Then I attached an led across the windings. I tested different connections. I found there was one arrangement where the led lit dimly.
I am not sure if I created an inductive coupling, or a step-up or step-down transformer, or what.