Al,
if i apply the 80% rule to a 14 wire, 15A circiut i come up with 1440W, or 8 locations per 220.3.B(11).

or lets just say we have an exclusive lighting circuit using 1440W at 8 locations, this would be fairly hard to run, switch loops and such, to a total lentgh of 81 feet.

besides that, those ideal testers are giving us a reading back to the x-former.