3 Wire Dryer Cord and Receptacle in a Mobile Home: Is It Legal?
A user asked the app about a mobile home with an old 3 wire dryer receptacle, a dryer fitted with a 4 wire cord, and a spare 3 wire cord on hand. The tempting move is to swap the cords and match the old receptacle. In a mobile home that is the wrong call, and it has been wrong for a very long time.
Why mobile homes are different
The general dryer rule lives in NEC 2023 Section 250.140. New installations must connect the frame of a dryer to an equipment grounding conductor, meaning a 4 wire circuit. The famous exception that allows an existing 3 wire dryer circuit to remain, with the frame grounded through the neutral, applies only to existing branch circuits in ordinary premises wiring, and it explicitly excludes mobile homes and recreational vehicles. Article 550 backs this up: Section 550.16(A) requires the grounded conductor (neutral) in a mobile home to be insulated and kept separate from the equipment grounding conductor all the way back to the service equipment, which sits outside the home at the pedestal. Bonding neutral to a dryer frame inside a mobile home is prohibited, full stop, and always has been under Article 550 going back generations of the Code.
The reason is structural. A mobile home is fed like a subpanel: the neutral to ground bond happens at the service pedestal, not in the home's panel. The chassis, skin, and gas lines are all bonded metal. If a 3 wire dryer connection loses its neutral, the dryer frame and potentially the chassis of the entire home ride up to line voltage through the appliance. In a site built house that failure energizes one appliance; in a mobile home it can energize the structure someone is leaning on.
The right fix
Keep the 4 wire cord on the dryer and replace the receptacle instead. Install a NEMA 14-30R, four wire, on the existing 30 amp circuit if that circuit contains a separate equipment grounding conductor, which mobile home wiring built to Article 550 should. Land the cord's green conductor on the grounding terminal and make sure the bonding strap inside the dryer between neutral and frame is removed, since that strap is only used with legacy 3 wire hookups. If the branch circuit truly has no grounding conductor, the circuit itself is not compliant for a mobile home and needs to be rewired, not adapted around.