Cooper Wiring Devices 1257 flush mount receptacle. Typically used for newer dryers that have a grounded plug and that require dual voltage: 250V for the heating element and 125V for the drum motor and controls. If you have an older dryer with a non-grounding plug (that is, a 3-blade plug), check out our NEMA 10-30 outlets. Commercial Specification Grade, NEMA 14-30R, 3-pole, 4-wire, grounding, rated 30A 125/250V. Fits wallplates with 2.147" or 2.15" diameter opening.