Current Sensor (mFi-CS) is a clip-on, alternating current (AC) sensor. It is designed for current monitoring of motors, lighting equipment, industrial hardware, or other AC electrical loads. 

For use with mFi mPort hardware and mFi Controller software (included with the mFi mPort). 

Connection Type: mFi RJ45 
Input Current: 0-100A 

http://dl.ubnt.com/datasheets/mfi/mFi_Datasheet_V10_6-28-12.pdf

http://dl.ubnt.com/guides/mfi/mFi-CS_QSG_V10_4-25-12.pdf