I'm attacking this project with some knowledge of programming but little on the electronics side.  I was wondering if there's any benefit to including fuse(s) in the circuit that we'll be creating.  The project will include the non-invasive power monitoring with a CT and a voltage monitoring.  Aside from the AC-AC input the other sensors and circuit I intend to be powered by an Arduino.

Would it be prudent to include a fuse between the board and the 9V AC input for example?  If so, how do you select a size to suit?  I note in the designs here I don't see any, but don't know enough to know why.

Thanks, Geoff