In article ,
Chas Hurst wrote:

I think it's reference to insulation or lack of. With no insulation the
wire dissipates heat faster, hence the higher rating.


Knob and tube is insulated. It's exactly what I said. The gauge of the
wire is thicker. K&t used 12 gauge wire for 15 amp circuits. Most 15 amp
circuits now use 14 gauge wire.


Dimitri