Section 550.12/Mobile and Manufactured Home Service Equipment
NEC 550.12 covers service equipment requirements for mobile and manufactured homes including disconnecting means, panelboard rating, and bonding of the grounded conductor.
Mobile and manufactured homes must have a service disconnecting means and overcurrent protection located in sight of and not more than 30 feet from the exterior wall of the home, or mounted on the exterior wall. The disconnecting means must be rated not less than the calculated load per Article 550 Part III. The service equipment must have a rating of not less than 100 amperes for single-wide homes. The neutral (grounded conductor) and equipment grounding conductor must be separated in the mobile home panelboard (4-wire feeder), with the neutral-to-ground bond made only at the service equipment, not in the home's distribution panel. This differs from a standard residential service where the bond is at the main panel inside the house. A feeder from the service equipment to the mobile home must use a 4-wire system (two ungrounded, one grounded, one equipment grounding) per Section 550.16. The service equipment must be suitable for outdoor use and accessible to the serving utility.
Why this section exists
Mobile and manufactured homes are factory-built and transported to the site, creating a unique electrical arrangement where the service equipment is separate from the home's distribution panel. The 30-foot distance limit ensures the service disconnect is near the home for emergency access. The 4-wire feeder requirement (separate neutral and ground) prevents objectionable current on the metal frame and chassis of the home, which would create a shock hazard for anyone touching the frame. In a standard house, the neutral-to-ground bond in the main panel is acceptable because the panel is permanently attached to the building grounding system. A mobile home's frame is its grounding electrode, so separating neutral and ground prevents the frame from carrying return current.
What plan reviewers look for
Plan reviewers check the site electrical plan for the service equipment location relative to the mobile home (within 30 feet, within sight). They verify the service rating is at least 100 amperes. They check the feeder for 4-wire configuration (no combined neutral/ground). They verify the neutral is isolated (floating) in the mobile home panelboard. They check for a grounding electrode at the service equipment per Section 250.24.