These old Paragon kilns are wired differently than most kilns these days. They are 120/240V, meaning some of the time the switches cause the elements to run on 120V and other times the elements use 240V. Consequently, the 4-wire plug and receptacle with a neutral is essential.  The kiln will not operate properly on a conventional 3-wire 240V circuit. As Marko notes, a 30 amp circuit is minimum, but 40 amps is maximum.  The outlet on the top of the control box is actually 120/240V, and was intend