Maximum cord diameter 0.875 In. Can be used with either 30A or 50A 3-wire cord. 2 interchangeable neutral prongs are supplied (L-prong for 30A, flat prong for 50A). 30A/125/250V, NEMA 10-30P. 50A/125/250V, NEMA 10-50P. UL (Underwriter's Laboratories) listed.