Keeping the main breaker from tripping

[Chadfrom308]

For current readings, we are using the IC from this board:
http://www.panucatt.com/Current_Sens..._p/cs-100a.htm

I don't use this for FIRST, but on the Formula SAE team I am on, we are using this to read the alternator current and the total current output by the PDB.

I don't know exactly if it is legal to put this in between the board and breaker, in fact, I'm pretty sure it's not. Also, we use either a 150a or 200a version of this, I cannot remember. It is like $17 minimum order for these of digikey (I think, I didn't order them)