1) If the dryer circuit contains 4 wires....ie....... 2 hots, 1 neutral and 1 equipment ground, the receptacle is required to be a 4 prong and the cord will also be a 4 prong.
2) If the dryer circuit contains 3 wires......ie..........2 hots and 1 neutral, the receptacle is required to be a 3 prong and the cord will also be a 3 prong. If a 3 wire circuit, the neutral conductor at the dryer frame terminal block needs to get jumpered and bonded to the dryer frame green ground screw. The dryer terminal block may either contain a jumper strap or will require a short piece of 10 AWG Copper green insulated wire to jumper from the neutral terminal screw (middle terminal) on the back of the dryer to the frame green ground screw. This is how a 3 wire dryer circuit gets grounded.
3) All 240 volt electric dryers require a neutral conductor in addition to the 2 hot conductors for the circuit feed. If the circuit was installed prior to 1996, then a good chance the circuit will only be a 3 wire circuit without a ground. If the circuit was installed after 1996, the circuit should be a 4 wire using a separate ground wire.
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