Detect if a 3 phase AC submersible pump is on I need to know when a 3 phase AC submersible pump is turned on, for the sake of logging it to a online database. Thing is, I do not know how tell if it is ON, or OFF. I've given a thought to using a current transformer, specifically the "STC-013-30" one, but it requires to be wrapped around one of the AC wires (live/neutral) but the motor i have has both the wires insulated together forming a single, huge wire. Plus, its 3 phase, and I do now know if the STC can detect 3 phase currents. Can it be done some way? Can I utilise some other tool to tell if the motor is ON?
It's likely that the power to the motor is originating at a panel with breakers. You should be able to confirm that only one breaker set is being used to power the pump motor. At that location, all the wires are separated.

If you do not have the necessary skill to identify the correct wires, consider to consult an electrician. It is advisable to remove power to the panel before you begin to insert your fingers to wrap the sensor wire around the correct lead.