Three typical locations depending on the house construction.. One being right outside by the power meter.. OR in the attic usally near the access location.. or three in a special panel inside (laundry room, garage, master bedroom closet) Commonly called an "on-q" panel (at least here because they are the dominate company installing such panels)
if the cables are prewired when the house was built Id first check outside, usally they will just leave a bunch of cables hanging out the side of the house near the power meter... Unless its in a panel.. If its in the panel it makes it easier for ya.