To switch from a 4 prong to a 3 prong. First remove 4 prong cord, save screws you will need them. Look a 3 prong, it will be flat with 3 wires next to each other with metal fittings on the ends. The 2 outside which are hot wires go to the outside screws on the block, and the center which is neutral goes in the center. The only difference in the cords is the 4 prong has a ground, in new construction this is code. You don't need a ground if house is wired for a 3 prong.
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To switch from a 4 prong to a 3 prong. First remove 4 prong cord, save screws you will need them. Look a 3 prong, it will be flat with 3 wires next to each other with metal fittings on the ends. The 2 outside which are hot wires go to the outside screws on the block, and the center which is neutral goes in the center. The only difference in the cords is the 4 prong has a ground, in new construction this is code. You don't need a ground if house is wired for a 3 prong.