What current transformer do I need?
Image source: All Electronics.
Judging by this catalog extract and various other images on the web it is a two terminal meter so it is really only an ammeter with a scale calibrated to indicate power drawn from a 125 V supply with a resistive load. The non-linear scale is due to the square term in P = I2R but it may be compounded if the meter movement is moving iron type. If your voltage deviates from 125 V the power reading will not reflect this. I'd consider the meter as &quot;confirming a hunch&quot; rather than as an accurate instrument.
I suspect that you just connect it in series with the load. No current transformer. Inspect it to assess whether or not you think the internal wiring is capable of 30 A and try it with a 1 kW load - a kettle or heater.