Is there any way to infer the gauge of the wires inside an NM cable from the size and shape of the cable? I reckon a round cable is generally -/3 W/G and a flatter cable -/2 W/G, but I do not know how to distinguish 14/2 W/G from 12/2 W/G without readable markings.
I am mapping house circuits and have run across some NM cable whose markings have faded into nonexistence or were never present (might be 1980s cable, and I am ignorant of 1980s cable manufacture practices). Some text was embossed into the cable sheathing during manufacture, but the visible run is short and I cannot read the desired information off the cable.
I have a bunch of 20A breakers and am concerned the cable running out might be 14/2 W/G rather than 12/2 W/G, which I understand would mean the cable is undersized for the circuit amperage.