This is the SeeedStudio Non-Invasive AC Current Sensor (30A Max). It is a non-invasive current transformer. Use this sensor clip to build your own personal energy monitor. It is suitable for the current measuring monitoring and protection of AC motor lighting equipment, air compressor and so on. It is made with Ferrite core material and it's opening size 13mm x 13mm meets your requirements.
I needed a means to monitor my new heat pump, specifically to know when it was more economical to switch to natural gas. This required constant measurement of power so I connected the sensor to an Arduino to measure current and connected an AC output wall wart to measure voltage. The Arduino data was sent on to a Raspberry Pi which handles all the calculations and graphing as well as a live web page. Results compare very closely to published specs. PS. I double looped the power wire through the sensor to increase the sensitivity from 0-30A to 0-15A.