I have an old 250-V dryer recepticle with 3 slots. I bought a used Kenmore dryer that has a 4-prong plug. The wire in the house is a 1958 vintage, 3-wire cable coming from a 30 AMP breaker. The conduit is mounted on a cynder block basement wall, but there's no ground cable. Can I replace the 3 slot recepticle with a 4 slot recepticle?