This chart is for single conductor copper wire. If you are running your wire in conduit like our "Kiln's Electrical System" image shows, the issue becomes a little more complicated, but this chart gives you an idea of what size of wiring you will need to carry the load for your kiln. There is a problem when you bundle wiring in a conduit because the ability of the wiring to dissipate heat generated by the conduction of power is diminished. It is important to consult your electrical contractor to receive advise on this issue. Here is a link to a site with more information:
wire gauges