See https://www.youtube.com/video/vr4amblBu4g
In this video, we demonstrate how to change a single-phase kiln into a three-phase L&L Easy-Fire or School-Master kiln.
Although this video is specific to these kiln series, the basic principle applies to most 280 and 240-volt kilns. Kilns with higher amperage will not have the cord, but all 208 and 240-volt kilns can do the same easy change at the terminal block.