Article 550

Mobile Homes, Manufactured Homes, and Mobile Home Parks

Part I. General

  1. Scope. The provisions of this article cover the electrical conductors and equipment installed within or on mobile and manufactured homes, the conductors that connect mobile and manufactured homes to a supply of electricity, and the installa‐ tion of electrical wiring, luminaires, equipment, and appurte‐ nances related to electrical installations within a mobile home park up to the mobile home service-entrance conductors or, if none, the mobile home service equipment.Informational Note: For additional information on manufac‐ tured housing see NFPA 501-2013, Standard on Manufactured Housing, and Part 3280, Manufactured Home Construction and Safety Standards, of the Federal Department of Housing and Urban Development.
  2. Definitions.

Appliance, Fixed. An appliance that is fastened or otherwise secured at a specific location.

Appliance, Portable. An appliance that is actually moved or can easily be moved from one place to another in normal use.

Informational Note: For the purpose of this article, the follow‐ ing major appliances, other than built-in, are considered porta‐ ble if cord connected: refrigerators, range equipment, clothes washers, dishwashers without booster heaters, or other similar appliances.

Feeder Assembly. The overhead or under-chassis feeder conductors, including the grounding conductor, together with the necessary fittings and equipment or a power-supply cord listed for mobile home use, identified for the delivery of energy from the source of electrical supply to the panelboard within the mobile home.

Laundry Area. An area containing or designed to contain a laundry tray, clothes washer, or a clothes dryer.


which in the traveling mode is 2.4 m (8 ft)

Manufactured Home. A structure, transportable in one or


(40 ft)

electrical grounding system. The bonding conductor shall be solid copper, insulated, covered or bare, and not smaller than 8 AWG. The means of bonding to wire mesh or conductive

more sections, image more in width or 12.2 m

or or more in length, or when

elements shall be by pressure connectors or clamps of brass, copper, copper alloy, or an equally substantial approved means. Slatted floors that are supported by structures that are a part of an equipotential plane shall not require bonding.

Informational Note No. 1: Methods to establish equipotential planes are described in American Society of Agricultural and

erected on site is 29.77 m2 (320 ft2) or more is built on a

any structure that meets all the

permanent chassis and is designed to be used as a dwelling with or without a permanent foundation, whether or not connected to the utilities, and includes plumbing, heating, air condition‐ ing, and electrical systems contained therein. The term manu‐ factured home includes

requirements of this paragraph except the size requirements and with respect to which the manufacturer voluntarily files a certification required by the regulatory agency. Calculations used to determine the number of square meters (square feet) in a structure are based on the structure’s exterior dimensions and include all expandable rooms, cabinets, and other projec‐ tions containing interior space, but do not include bay windows [501:1.2.14]. For the purpose of this Code and unless otherwise indicated, the term mobile home includes manufactured homes and excludes park trailers defined in Article 552.4.

Informational Note No. 1: See the applicable building code for definition of the term permanent foundation.

Informational Note No. 2: See 24 CFR Part 3280, Manufactured Home Construction and Safety Standards, of the Federal Department of Housing and Urban Development, for additional information on the definition.

Mobile Home. A factory-assembled structure or structures transportable in one or more sections that are built on a permanent chassis and designed to be used as a dwelling with‐ out a permanent foundation where connected to the required utilities and that include the plumbing, heating, air- conditioning, and electrical systems contained therein.

For the purpose of this Code and unless otherwise indicated, the term mobile home includes manufactured homes.

Mobile Home Accessory Building or Structure. Any awning, cabana, ramada, storage cabinet, carport, fence, windbreak, or porch established for the use of the occupant of the mobile home on a mobile home lot.

Mobile Home Lot. A designated portion of a mobile home park designed for the accommodation of one mobile home and its accessory buildings or structures for the exclusive use of its occupants.

Mobile Home Park. A contiguous parcel of land that is used for the accommodation of occupied mobile homes.

Mobile Home Service Equipment. The equipment containing the disconnecting means, overcurrent protective devices, and receptacles or other means for connecting a mobile home feeder assembly.

Park Electrical Wiring Systems. All of the electrical wiring, luminaires, equipment, and appurtenances related to electrical installations within a mobile home park, including the mobile home service equipment.

550.4 General Requirements.

  1. Mobile Home Not Intended as a Dwelling Unit. A mobile home not intended as a dwelling unit — for example, those equipped for sleeping purposes only, contractor’s on-site offi‐ ces, construction job dormitories, mobile studio dressing rooms, banks, clinics, mobile stores, or intended for the display or demonstration of merchandise or machinery — shall not be required to meet the provisions of this article pertaining to the number or capacity of circuits required. It shall, however, meet all other applicable requirements of this article if provided with an electrical installation intended to be energized from a 120-volt or 120/240-volt ac power supply system. Where differ‐ ent voltage is required by either design or available power supply system, adjustment shall be made in accordance with other articles and sections for the voltage used.
  2. In Other Than Mobile Home Parks. Mobile homes instal‐ led in other than mobile home parks shall comply with the provisions of this article.
  3. Connection to Wiring System. The provisions of this arti‐ cle shall apply to mobile homes intended for connection to a wiring system rated 120/240 volts, nominal, 3-wire ac, with a grounded neutral conductor.
  4. Listed and Labeled. All electrical materials, devices, appli‐ ances, fittings, and other equipment shall be listed and labeled by a qualified testing agency and shall be connected in an approved manner when installed.

Part II. Mobile and Manufactured Homes

  1. Power Supply.
    1. Feeder. The power supply to the mobile home shall be a feeder assembly consisting of not more than one listed 50- ampere mobile home power-supply cord or a permanently installed feeder.Exception No. 1: A mobile home that is factory equipped with gas or oil- fired central heating equipment and cooking appliances shall be permit‐ ted to be provided with a listed mobile home power-supply cord rated 40 amperes.Exception No. 2: A feeder assembly shall not be required for manufac‐ tured homes constructed in accordance with 550.32(B).
    2. Power-Supply Cord. If the mobile home has a power- supply cord, it shall be permanently attached to the panel‐ board, or to a junction box permanently connected to the panelboard, with the free end terminating in an attachment plug cap.Cords with adapters and pigtail ends, extension cords, and similar items shall not be attached to, or shipped with, a mobile home.A suitable clamp or the equivalent shall be provided at the panelboard knockout to afford strain relief for the cord to prevent strain from being transmitted to the terminals when the power-supply cord is handled in its intended manner.The cord shall be a listed type with four conductors, one of which shall be identified by a continuous green color or a continuous green color with one or more yellow stripes for use as the grounding conductor.
    3. Attachment Plug Cap. The attachment plug cap shall be a 3-pole, 4-wire, grounding type, rated 50 amperes, 125/250 volts with a configuration as shown in Figure 550.10(C) and inten‐ ded for use with the 50-ampere, 125/250-volt receptacle config‐ uration shown in Figure 550.10(C). It shall be listed, by itself or as part of a power-supply cord assembly, for the purpose and shall be molded to or installed on the flexible cord so that it is secured tightly to the cord at the point where the cord enters the attachment plug cap. If a right-angle cap is used, the configuration shall be oriented so that the grounding member is farthest from the cord.Informational Note: Complete details of the 50-ampere plug and receptacle configuration can be found in ANSI/NEMA WD 6-2002 (R2008), Standard for Dimensions of Attachment Plugs and Receptacles, Figure 14-50.

      imageGXYWCapto be combined with the disconnecting means as a single assembly. Such a combination shall be permitted to be designa‐ ted as a panelboard. If a fused panelboard is used, the maxi‐ mum fuse size for the mains shall be plainly marked with lettering at least 6 mm (1∕4 in.) high and visible when fuses are changed.125/250-V, 50-A, 3-pole, 4-wire, grounding type
      FIGURE 550.10(C) 50-Ampere, 125/250-Volt Receptacle and Attachment Plug Cap Configurations, 3-Pole, 4-Wire, Grounding-Types, Used for Mobile Home Supply Cords and Mobile Home Parks.
    4. Overall Length of a Power-Supply Cord. The overall length of a power-supply cord, measured from the end of the cord, including bared leads, to the face of the attachment plug cap shall not be less than 6.4 m (21 ft) and shall not exceed 11 m (361∕2 ft). The length of the cord from the face of the attachment plug cap to the point where the cord enters the mobile home shall not be less than 6.0 m (20 ft).
    5. Marking. The power-supply cord shall bear the following marking:FOR USE WITH MOBILE HOMES — 40 AMPERESorFOR USE WITH MOBILE HOMES — 50 AMPERES
    6. Point of Entrance. The point of entrance of the feeder assembly to the mobile home shall be in the exterior wall, floor, or roof.
    7. Protected. Where the cord passes through walls or floors, it shall be protected by means of conduits and bushings or equivalent. The cord shall be permitted to be installed within the mobile home walls, provided a continuous raceway having a maximum size of 32 mm (11∕4 in.) is installed from the branch- circuit panelboard to the underside of the mobile home floor.
    8. Protection Against Corrosion and Mechanical Damage. Permanent provisions shall be made for the protection of the attachment plug cap of the power-supply cord and any connec‐ tor cord assembly or receptacle against corrosion and mechani‐ cal damage if such devices are in an exterior location while the mobile home is in transit.
    9. Mast Weatherhead or Raceway. Where the calculated load exceeds 50 amperes or where a permanent feeder is used, the supply shall be by means of either of the following:
    1. One mast weatherhead installation, installed in accord‐ ance with Article 230, containing four continuous, insula‐ ted, color-coded feeder conductors, one of which shall be an equipment grounding conductor
    2. A metal raceway or rigid nonmetallic conduit from the disconnecting means in the mobile home to the under‐ side of the mobile home, with provisions for the attach‐ ment to a suitable junction box or fitting to the raceway on the underside of the mobile home [with or without conductors as in 550.10(I)(1)]. The manufacturer shall provide written installation instructions stating the proper feeder conductor sizes for the raceway and the size of the junction box to be used.
  2. Disconnecting Means and Branch-Circuit Protective Equipment. The branch-circuit equipment shall be permittedWhere plug fuses and fuseholders are used, they shall be tamper-resistant Type S, enclosed in dead-front fuse panel‐ boards. Electrical panelboards containing circuit breakers shall also be dead-front type.Informational Note: See 110.22 concerning identification of each disconnecting means and each service, feeder, or branch circuit at the point where it originated and the type marking needed.
    1. Disconnecting Means. A single disconnecting means shall be provided in each mobile home consisting of a circuit breaker, or a switch and fuses and its accessories installed in a readily accessible location near the point of entrance of the supply cord or conductors into the mobile home. The main circuit breakers or fuses shall be plainly marked “Main.” This equipment shall contain a solderless type of grounding connec‐ tor or bar for the purposes of grounding, with sufficient termi‐ nals for all grounding conductors. The terminations of the grounded circuit conductors shall be insulated in accordance with 550.16(A). The disconnecting equipment shall have a rating not less than the calculated load. The distribution equip‐ ment, either circuit breaker or fused type, shall be located a minimum of 600 mm (24 in.) from the bottom of such equip‐ ment to the floor level of the mobile home.Informational Note: See 550.20(B) for information on discon‐ necting means for branch circuits designed to energize heating or air-conditioning equipment, or both, located outside the mobile home, other than room air conditioners.A panelboard shall be rated not less than 50 amperes and employ a 2-pole circuit breaker rated 40 amperes for a 40-ampere supply cord, or 50 amperes for a 50-ampere supply cord. A panelboard employing a disconnect switch and fuses shall be rated 60 amperes and shall employ a single 2-pole, 60- ampere fuseholder with 40- or 50-ampere main fuses for 40- or 50-ampere supply cords, respectively. The outside of the panel‐ board shall be plainly marked with the fuse size.The panelboard shall be located in an accessible location but shall not be located in a bathroom or a clothes closet. A clear working space at least 750 mm (30 in.) wide and 750 mm (30 in.) in front of the panelboard shall be provided. This space shall extend from the floor to the top of the panelboard.
    2. Branch-Circuit Protective Equipment. Branch-circuit distribution equipment shall be installed in each mobile home and shall include overcurrent protection for each branch circuit consisting of either circuit breakers or fuses.The branch-circuit overcurrent devices shall be rated as follows:
      1. Not more than the circuit conductors; and
      2. Not more than 150 percent of the rating of a single appli‐ ance rated 13.3 amperes or more that is supplied by an individual branch circuit; but
      3. Not more than the overcurrent protection size and of the type marked on the air conditioner or other motor- operated appliance.
    3. Two-Pole Circuit Breakers. Where circuit breakers are provided for branch-circuit protection, 240-volt circuits shall be protected by a 2-pole common or companion trip, or by circuit breakers with identified handle ties.
    4. Electrical Nameplates. A metal nameplate on the outside adjacent to the feeder assembly entrance shall read as follows:
    THIS CONNECTION FOR 120/240-VOLT, 3-POLE, 4-WIRE, 60-HERTZ,           AMPERE SUPPLYThe correct ampere rating shall be marked in the blank space.Exception: For manufactured homes, the manufacturer shall provide in its written installation instructions or in the data plate the minimum ampere rating of the feeder assembly or, where provided, the service- entrance conductors intended for connection to the manufactured home. The rating provided shall not be less than the minimum load calculated in accordance with 550.18.
  3. Branch Circuits. The number of branch circuits required shall be determined in accordance with 550.12(A) through (E).
    1. Lighting. The number of branch circuits shall be based on 33 volt-amperes/m2 (3 VA/ft2) times outside dimensions of the mobile home (coupler excluded) divided by 120 volts to determine the number of 15- or 20-ampere lighting area circuits, for example,
      [550.12(A)]3  length  width 120  15 or 20 No. of 15- or 20-  ampere circuits
    2. Small Appliances. In kitchens, pantries, dining rooms, and breakfast rooms, two or more 20-ampere small-appliance circuits, in addition to the number of circuits required else‐ where in this section, shall be provided for all receptacle outlets required by 550.13(D) in these rooms. Such circuits shall have no other outlets.Exception No. 1: Receptacle outlets installed solely for the electrical supply and support of an electric clock in any the rooms specified in 550.12(B) shall be permitted.Exception No. 2: Receptacle outlets installed to provide power for supplemental equipment and lighting on gas-fired ranges, ovens, or counter-mounted cooking units shall be permitted.Exception No. 3: A single receptacle for refrigeration equipment shall be permitted to be supplied from an individual branch circuit rated 15 amperes or greater.Countertop receptacle outlets installed in the kitchen shall be supplied by not less than two small-appliance circuit branch circuits, either or both of which shall be permitted to supply receptacle outlets in the kitchen and other locations specified in 550.12(B).
    3. Laundry Area. Where a laundry area is provided, a 20-ampere branch circuit shall be provided to supply the laun‐ dry receptacle outlet(s). This circuit shall have no other outlets.
    4. General Appliances. (Including furnace, water heater, range, and central or room air conditioner, etc.). There shall be one or more circuits of adequate rating in accordance with the following:Informational Note: For central air conditioning, see Article 440.
      1. The ampere rating of fixed appliances shall be not over 50 percent of the circuit rating if lighting outlets (recep‐ tacles, other than kitchen, dining area, and laundry, considered as lighting outlets) are on the same circuit.
      2. For fixed appliances on a circuit without lighting outlets, the sum of rated amperes shall not exceed the branch- circuit rating. Motor loads or continuous loads shall not exceed 80 percent of the branch-circuit rating.
      3. The rating of a single cord-and-plug-connected appliance on a circuit having no other outlets shall not exceed 80 percent of the circuit rating.
      4. The rating of a range branch circuit shall be based on the range demand as specified for ranges in 550.18(B)(5).
    5. Bathrooms. Bathroom receptacle outlets shall be supplied by at least one 20-ampere branch circuit. Such circuits shall have no outlets other than as provided for in 550.13(E)(2).
  4. Receptacle Outlets.
    1. Grounding-Type Receptacle Outlets. All receptacle outlets shall comply with the following:
      1. Be of grounding type
      2. Be installed according to 406.4
      3. Except where supplying specific appliances, be 15- or 20- ampere, 125-volt, either single or multiple type, and accept parallel-blade attachment plugs
    2. Ground-Fault Circuit Interrupters (GFCI). All 125-volt, single-phase, 15- and 20-ampere receptacle outlets installed in the locations specified in 550.13(B)(1) through (5) shall have GFCI protection for personnel.
      1. Outdoors, including compartments accessible from outside the unitimage
      2. Bathrooms, including receptacles in luminaires
      3. Kitchens, where receptacles are installed to serve counter‐ top surfaces
      4. Sinks, where receptacles are installed within 1.8 m (6 ft) of the outer edge of the sinkInformational Note: For information on protection of dishwash‐ers, see 422.5.
      5. Dishwashers

    3. Cord-Connected Fixed Appliance. A grounding-typereceptacle outlet shall be provided for each cord-connected fixed appliance installed.
    4. Receptacle Outlets Required. Except in the bath, closet, and hallway areas, receptacle outlets shall be installed at wall spaces 600 mm (2 ft) wide or more so that no point along the floor line is more than 1.8 m (6 ft) measured horizontally from an outlet in that space. In addition, a receptacle outlet shall be installed in the following locations:
      1. Over or adjacent to countertops in the kitchen [at least one on each side of the sink if countertops are on each side and are 300 mm (12 in.) or over in width].
      2. Adjacent to the refrigerator and freestanding gas-range space. A multiple-type receptacle shall be permitted to serve as the outlet for a countertop and a refrigerator.
      3. At countertop spaces for built-in vanities.
      4. At countertop spaces under wall-mounted cabinets.
      5. In the wall at the nearest point to where a bar-type coun‐ ter attaches to the wall.
      6. In the wall at the nearest point to where a fixed room divider attaches to the wall.
      7. In laundry areas within 1.8 m (6 ft) of the intended loca‐ tion of the laundry appliance(s).
      8. At least one receptacle outlet located outdoors and acces‐ sible at grade level and not more than 2.0 m (61∕2 ft) above grade. A receptacle outlet located in a compart‐ ment accessible from the outside of the unit shall be considered an outdoor receptacle.
      9. At least one receptacle outlet shall be installed in bath‐ rooms within 900 mm (36 in.) of the outside edge of each basin. The receptacle outlet shall be located above or adjacent to the basin location. This receptacle shall be in addition to any receptacle that is a part of a luminaire or appliance. The receptacle shall not be enclosed within a bathroom cabinet or vanity.
    5. Pipe Heating Cable(s) Outlet. For the connection of pipe heating cable(s), a receptacle outlet shall be located on the underside of the unit as follows:
      1. Within 600 mm (2 ft) of the cold water inlet.
      2. Connected to an interior branch circuit, other than a small-appliance branch circuit. It shall be permitted to use a bathroom receptacle circuit for this purpose.
      3. On a circuit where all of the outlets are on the load side of the ground-fault circuit-interrupter.
      4. This outlet shall not be considered as the receptacle required by 550.13(D)(8).
    6. Receptacle Outlets Not Permitted. Receptacle outlets shall not be permitted in the following locations:
      1. Receptacle outlets shall not be installed within or directly over a bathtub or shower space.
      2. A receptacle shall not be installed in a face-up position in any countertop.
      3. Receptacle outlets shall not be installed above electric baseboard heaters, unless provided for in the listing or manufacturer’s instructions.
    7. Receptacle Outlets Not Required. Receptacle outlets shall not be required in the following locations:
    1. In the wall space occupied by built-in kitchen or ward‐ robe cabinets
    2. In the wall space behind doors that can be opened fully against a wall surface
    3. In room dividers of the lattice type that are less than2.5 m (8 ft) long, not solid, and within 150 mm (6 in.) of the floor
    4. In the wall space afforded by bar-type counters
  5. Luminaires and Appliances.
    1. Fasten Appliances in Transit. Means shall be provided to securely fasten appliances when the mobile home is in transit. (See 550.16 for provisions on grounding.)
    2. Accessibility. Every appliance shall be accessible for inspection, service, repair, or replacement without removal of permanent construction.
    3. Pendants. Listed pendant-type luminaires or pendant cords shall be permitted.
    4. Bathtub and Shower Luminaires. Where a luminaire is installed over a bathtub or in a shower stall, it shall be of the enclosed and gasketed type listed for wet locations.
  6. Wiring Methods and Materials. Except as specifically limited in this section, the wiring methods and materials inclu‐ ded in this Code shall be used in mobile homes. Aluminum conductors, aluminum alloy conductors, and aluminum core conductors such as copper-clad aluminum shall not be accepta‐ ble for use as branch-circuit wiring.
    1. Nonmetallic Boxes. Nonmetallic boxes shall be permitted only with nonmetallic cable or nonmetallic raceways.
    2. Nonmetallic Cable Protection. Nonmetallic cable located 380 mm (15 in.) or less above the floor, if exposed, shall be protected from physical damage by covering boards, guard strips, or raceways. Cable likely to be damaged by stowage shall be so protected in all cases.
    3. Metal-Covered and Nonmetallic Cable Protection. Metal- covered and nonmetallic cables shall be permitted to pass through the centers of the wide side of 2 by 4 studs. However, they shall be protected where they pass through 2 by 2 studs or at other studs or frames where the cable or armor would be less than 32 mm (11∕4 in.) from the inside or outside surface of the studs where the wall covering materials are in contact with the studs. Steel plates on each side of the cable, or a tube, with not less than 1.35 mm (0.053 in.) wall thickness shall be required to protect the cable. These plates or tubes shall be securely held in place.
    4. Metal Faceplates. Where metal faceplates are used, they shall be grounded.
    5. Installation Requirements. Where a range, clothes dryer, or other appliance is connected by metal-covered cable or flexi‐ ble metal conduit, a length of not less than 900 mm (3 ft) of unsupported cable or conduit shall be provided to service the appliance. The cable or flexible metal conduit shall be secured to the wall. Type NM or Type SE cable shall not be used to connect a range or dryer. This shall not prohibit the use of Type NM or Type SE cable between the branch-circuit overcur‐ rent protective device and a junction box or range or dryer receptacle.
    6. Raceways. Where rigid metal conduit or intermediate metal conduit is terminated at an enclosure with a locknut and bushing connection, two locknuts shall be provided, one inside and one outside of the enclosure. Rigid nonmetallic conduit, electrical nonmetallic tubing, or surface raceway shall be permitted. All cut ends of conduit and tubing shall be reamed or otherwise finished to remove rough edges.
    7. Switches. Switches shall be rated as follows:
      1. For lighting circuits, switches shall be rated not less than 10 amperes, 120 to 125 volts, and in no case less than the connected load.
      2. Switches for motor or other loads shall comply with the provisions of 404.14.
    8. Under-Chassis Wiring (Exposed to Weather).
      1. Where outdoor or under-chassis line-voltage (120 volts, nominal, or higher) wiring is exposed, it shall be protected by a conduit or raceway identified for use in wet locations. The conductors shall be listed for use in wet locations.
      2. Where wiring is exposed to physical damage, it shall be protected by a raceway, conduit, or other means.
    1. Boxes, Fittings, and Cabinets. Boxes, fittings, and cabinets shall be securely fastened in place and shall be supported from a structural member of the home, either directly or by using a substantial brace.Exception: Snap-in-type boxes. Boxes provided with special wall or ceil‐ ing brackets and wiring devices with integral enclosures that securely fasten to walls or ceilings and are identified for the use shall be permit‐ ted without support from a structural member or brace. The testing and approval shall include the wall and ceiling construction systems for which the boxes and devices are intended to be used.
    2. Appliance Terminal Connections. Appliances having branch-circuit terminal connections that operate at tempera‐ tures higher than 60°C (140°F) shall have circuit conductors as described in the following:
      1. Branch-circuit conductors having an insulation suitable for the temperature encountered shall be permitted to be run directly to the appliance.
      2. Conductors having an insulation suitable for the tempera‐ ture encountered shall be run from the appliance termi‐ nal connection to a readily accessible outlet box placed at least 300 mm (1 ft) from the appliance. These conductors shall be in a suitable raceway or Type AC or MC cable of at least 450 mm (18 in.) but not more than 1.8 m (6 ft) in length.
    3. Component Interconnections. Fittings and connectors that are intended to be concealed at the time of assembly shall be listed and identified for the interconnection of building components. Such fittings and connectors shall be equal to the wiring method employed in insulation, temperature rise, and fault-current withstanding and shall be capable of enduring the vibration and shock occurring in mobile home transportation.
    Informational Note: See 550.19 for interconnection of multiple section units.
  7. Grounding. Grounding of both electrical and nonelec‐ trical metal parts in a mobile home shall be through connec‐ tion to a grounding bus in the mobile home panelboard and shall be connected through the green-colored insulated conductor in the supply cord or the feeder wiring to the grounding bus in the service-entrance equipment located adja‐ cent to the mobile home location. Neither the frame of the mobile home nor the frame of any appliance shall be connec‐ ted to the grounded circuit conductor in the mobile home. Where the panelboard is the service equipment as permitted by 550.32(B), the neutral conductors and the equipment ground‐ ing bus shall be connected.
    1. Grounded Conductor.
      1. Insulated. The grounded circuit conductor shall be insu‐ lated from the grounding conductors and from equipment enclosures and other grounded parts. The grounded circuit conductor terminals in the panelboard and in ranges, clothes dryers, counter-mounted cooking units, and wall-mounted ovens shall be insulated from the equipment enclosure. Bond‐ ing screws, straps, or buses in the panelboard or in appliances shall be removed and discarded. Where the panelboard is the service equipment as permitted by 550.32(B), the neutral conductors and the equipment grounding bus shall be connec‐ ted.
      2. Connections of Ranges and Clothes Dryers. Connections of ranges and clothes dryers with 120/240-volt, 3-wire ratings shall be made with 4-conductor cord and 3-pole, 4-wire, grounding-type plugs or by Type AC cable, Type MC cable, or conductors enclosed in flexible metal conduit.
    2. Equipment Grounding Means.
      1. Supply Cord or Permanent Feeder. The green-colored insulated grounding wire in the supply cord or permanent feeder wiring shall be connected to the grounding bus in the panelboard or disconnecting means.
      2. Electrical System. In the electrical system, all exposed metal parts, enclosures, frames, luminaire canopies, and so forth, shall be effectively bonded to the grounding terminal or enclosure of the panelboard.
      3. Cord-Connected Appliances. Cord-connected appliances, such as washing machines, clothes dryers, and refrigerators, and the electrical system of gas ranges and so forth, shall be grounded by means of a cord with an equipment grounding conductor and grounding-type attachment plug.
    3. Bonding of Non–Current-Carrying Metal Parts.
      1. Exposed Non–Current-Carrying Metal Parts. All exposed non–current-carrying metal parts that are likely to become energized shall be effectively bonded to the grounding termi‐ nal or enclosure of the panelboard. A bonding conductor shall be connected between the panelboard and an accessible termi‐ nal on the chassis.
      2. Grounding Terminals. Grounding terminals shall be of the solderless type and listed as pressure-terminal connectors recognized for the wire size used. The bonding conductor shall be solid or stranded, insulated or bare, and shall be 8 AWG copper minimum, or equivalent. The bonding conductor shall be routed so as not to be exposed to physical damage.
      3. Metallic Piping and Ducts. Metallic gas, water, and waste pipes and metallic air-circulating ducts shall be considered bonded if they are connected to the terminal on the chassis [see 550.16(C)(1)] by clamps, solderless connectors, or by suit‐ able grounding-type straps.
      4. Metallic Roof and Exterior Coverings. Any metallic roof and exterior covering shall be considered bonded if the follow‐ ing conditions are met:
    1. The metal panels overlap one another and are securely attached to the wood or metal frame parts by metallic fasteners.
    2. The lower panel of the metallic exterior covering is secured by metallic fasteners at a cross member of the chassis by two metal straps per mobile home unit or section at opposite ends.
    The bonding strap material shall be a minimum of 100 mm (4 in.) in width of material equivalent to the skin or a material of equal or better electrical conductivity. The straps shall be fastened with paint-penetrating fittings such as screws and star‐ washers or equivalent.
  8. Testing.
    1. Dielectric Strength Test. The wiring of each mobile home shall be subjected to a 1-minute, 900-volt, dielectric strength test (with all switches closed) between live parts (including neutral conductor) and the mobile home ground. Alterna‐
      tively, the test shall be permitted to be performed at 1080 volts for 1 second. This test shall be performed after branch circuits are complete and after luminaires or appliances are installed.Exception: Listed luminaires or appliances shall not be required to with‐ stand the dielectric strength test.
    2. Continuity and Operational Tests and Polarity Checks.
    Each mobile home shall be subjected to all of the following:(1) An electrical continuity test to ensure that all exposed
    1. Derive amperes for freestanding range (as distinguished from separate ovens and cooking units) by dividing the following values by 240 volts as shown in the table below:
    2. If outlets or circuits are provided for other than factory- installed appliances, include the anticipated load.
    Informational Note: Refer to Informative Annex D, Exam‐ ple D11, for an illustration of the application of this calculation.
    Useelectrically conductive parts are properly bondedequipment, except water heaters and electric furnaces, is0–10,00080 percent of ratingconnected and in working orderOver 10,000–12,5008,000(3) Electrical polarity checks of permanently wired equip‐Over 12,500–13,5008,400ment and receptacle outlets to determine that connec‐Over 13,500–14,5008,800(2) An electrical operational test to demonstrate that allNameplate Rating (watts)(volt-amperes)
    tions have been properly made
  9. Calculations. The following method shall be employed in calculating the supply-cord and distribution-panelboard load for each feeder assembly for each mobile home in lieu of the procedure shown in Article 220 and shall be based on a 3-wire, 120/240-volt supply with 120-volt loads balanced between the two ungrounded conductors of the 3-wire system.
    1. Lighting, Small-Appliance, and Laundry Load.
      1. Lighting Volt-Amperes. Length times width of mobile home floor (outside dimensions) times 33 volt-amperes/m2 (3 VA/ft2), for example, length × width × 3 = lighting volt- amperes.
      2. Small-Appliance Volt-Amperes. Number of circuits times 1500 volt-amperes for each 20-ampere appliance receptacle circuit (see definition of Appliance, Portable, with a fine print note in 550.2), for example, number of circuits × 1500 = small- appliance volt-amperes.
      3. Laundry Area Circuit Volt-Amperes. 1500 volt-amperes.
      4. Total Volt-Amperes. Lighting volt-amperes plus small- appliance volt-amperes plus laundry area volt-amperes equals total volt-amperes.
      5. Net Volt-Amperes. First 3000 total volt-amperes at 100 percent plus remainder at 35 percent equals volt-amperes to be divided by 240 volts to obtain current (amperes) per leg.
    2. Total Load for Determining Power Supply. Total load for determining power supply is the sum of the following:
      1. Lighting and small-appliance load as calculated in 550.18(A)(5)
      2. Nameplate amperes for motors and heater loads (exhaust fans, air conditioners, electric, gas, or oil heating). Omit smaller of the heating and cooling loads, except include blower motor if used as air-conditioner evaporator motor. Where an air conditioner is not installed and a 40-ampere power-supply cord is provided, allow 15 amperes per leg for air conditioning.
      3. Twenty-five percent of current of largest motor in item (2).
      4. Total of nameplate amperes for waste disposer, dish‐ washer, water heater, clothes dryer, wall-mounted oven, cooking units. Where the number of these appliances exceeds three, use 75 percent of total.
      Over 14,500–15,500 9,200Over 15,500–16,500 9,600Over 16,500–17,500 10,000
    3. Optional Method of Calculation for Lighting and Appli‐ ance Load. The optional method for calculating lighting and appliance load shown in 220.82 shall be permitted.
  10. Interconnection of Multiple-Section Mobile or Manu‐ factured Home Units.
    1. Wiring Methods. Approved and listed fixed-type wiring methods shall be used to join portions of a circuit that must be electrically joined and are located in adjacent sections after the home is installed on its support foundation. The circuit’s junc‐ tion shall be accessible for disassembly when the home is prepared for relocation.Informational Note: See 550.15(K) for component interconnec‐ tions.
    2. Disconnecting Means. Expandable or multiunit manufac‐ tured homes, not having permanently installed feeders, that are to be moved from one location to another shall be permit‐ ted to have disconnecting means with branch-circuit protective equipment in each unit when so located that after assembly or joining together of units, the requirements of 550.10 will be met.
  11. Outdoor Outlets, Luminaires, Air-Cooling Equipment, and So Forth.
  1. Listed for Outdoor Use. Outdoor luminaires and equip‐ ment shall be listed for wet locations or outdoor use. Outdoor receptacles shall comply with 406.9. Where located on the underside of the home or located under roof extensions or similarly protected locations, outdoor luminaires and equip‐ ment shall be listed for use in damp locations.
  2. Outside Heating Equipment, Air-Conditioning Equipment, or Both. A mobile home provided with a branch circuit designed to energize outside heating equipment, air- conditioning equipment, or both, located outside the mobile home, other than room air conditioners, shall have such branch-circuit conductors terminate in a listed outlet box, or disconnecting means, located on the outside of the mobile home. A label shall be permanently affixed adjacent to the outlet box and shall contain the following information:



           AMPERES, AT               VOLTS, 60 HERTZ,



The correct voltage and ampere rating shall be given. The tag shall be not less than 0.51 mm (0.020 in.) thick etched brass, stainless steel, anodized or alclad aluminum, or equiva‐ lent. The tag shall not be less than 75 mm by 45 mm (3 in. by 13∕4 in.) minimum size.

550.25 Arc-Fault Circuit-Interrupter Protection.

  1. Definition. Arc-fault circuit interrupters are defined in Article 100.
  2. Mobile Homes and Manufactured Homes. All 120-volt branch circuits that supply 15- and 20-ampere outlets shall comply with 210.12.

Part III. Services and Feeders

  1. Distribution System. The mobile home park secon‐ dary electrical distribution system to mobile home lots shall be single-phase, 120/240 volts, nominal. For the purpose of Part III, where the park service exceeds 240 volts, nominal, transformers and secondary panelboards shall be treated as services.
  2. Allowable Demand Factors. Park electrical wiring systems shall be calculated (at 120/240 volts) on the larger of the following:
    1. 16,000 volt-amperes for each mobile home lot
    2. The load calculated in accordance with 550.18 for the largest typical mobile home that each lot will accept
    It shall be permissible to calculate the feeder or service load in accordance with Table 550.31. No demand factor shall be allowed for any other load, except as provided in this Code.
  3. Service Equipment.
  1. Mobile Home Service Equipment. The mobile home serv‐ ice equipment shall be located adjacent to the mobile home and not mounted in or on the mobile home. The service equipment shall be located in sight from and not more than9.0 m (30 ft) from the exterior wall of the mobile home it serves. The service equipment shall be permitted to be located
    Number of Mobile HomesDemand Factor (%)11002553444395336297–92810–122713–152616–212522–402441–602361 and over22Table 550.31 Demand Factors for Services and Feederselsewhere on the premises, if a disconnecting means suitable for use as service equipment is located within sight from and not more than 9.0 m (30 ft) from the exterior wall of the mobile home it serves and is rated not less than that required for service equipment in accordance with 550.32(C). Ground‐ ing at the disconnecting means shall be in accordance with 250.32.
  2. Manufactured Home Service Equipment. The manufac‐ tured home service equipment shall be permitted to be instal‐ led in or on a manufactured home, provided that all of the following conditions are met:
    1. The manufacturer shall include in its written installation instructions information indicating that the home shall be secured in place by an anchoring system or installed on and secured to a permanent foundation.
    2. The installation of the service shall comply with Part I through Part VII of Article 230.
    3. Means shall be provided for the connection of a ground‐ ing electrode conductor to the service equipment and routing it outside the structure.
    4. Bonding and grounding of the service shall be in accord‐ ance with Part I through Part V of Article 250.
    5. The manufacturer shall include in its written installation instructions one method of grounding the service equip‐ ment at the installation site. The instructions shall clearly state that other methods of grounding are found in Arti‐ cle 250.
    6. The minimum size grounding electrode conductor shall be specified in the instructions.
    7. A red warning label shall be mounted on or adjacent to the service equipment. The label shall state the following:
    WARNINGDO NOT PROVIDE ELECTRICAL POWER UNTIL THE GROUNDING ELECTRODE(S) IS INSTALLED AND CONNECTED(SEE INSTALLATION INSTRUCTIONS).Where the service equipment is not installed in or on the unit, the installation shall comply with the other provisions of this section.
  3. Rating. Mobile home service equipment shall be rated at not less than 100 amperes at 120/240 volts, and provisions shall be made for connecting a mobile home feeder assembly by a permanent wiring method. Power outlets used as mobile home service equipment shall also be permitted to contain recepta‐ cles rated up to 50 amperes with appropriate overcurrent protection. Fifty-ampere receptacles shall conform to the configuration shown in Figure 550.10(C).Informational Note: Complete details of the 50-ampere plug and receptacle configuration can be found in ANSI/NEMA WD 6-2002 (Rev. 2008), Standard for Wiring Devices — Dimensional Requirements, Figure 14-50.
  4. Additional Outside Electrical Equipment. Means for connecting a mobile home accessory building or structure or additional electrical equipment located outside a mobile home by a fixed wiring method shall be provided in either the mobile home service equipment or the local external disconnecting means permitted in 550.32(A).
  5. Additional Receptacles. Additional receptacles shall be permitted for connection of electrical equipment located outside the mobile home, and all such 125-volt, single-phase, 15- and 20-ampere receptacles shall be protected by a listed ground-fault circuit interrupter.
  6. Mounting Height. Outdoor mobile home disconnecting means shall be installed so the bottom of the enclosure containing the disconnecting means is not less than 600 mm (2 ft) above finished grade or working platform. The discon‐ necting means shall be installed so that the center of the grip of the operating handle, when in the highest position, is not more than 2.0 m (6 ft 7 in.) above the finished grade or work‐ ing platform.
  7. Marking. Where a 125/250-volt receptacle is used in mobile home service equipment, the service equipment shall be marked as follows:


The marking shall be located on the service equipment adja‐ cent to the receptacle outlet.

550.33 Feeder.

  1. Feeder Conductors. Feeder conductors shall comply with the following:
    1. Feeder conductors shall consist of either a listed cord, factory installed in accordance with 550.10(B), or a permanently installed feeder consisting of four insulated, color-coded conductors that shall be identified by the factory or field marking of the conductors in compliance with 310.110. Equipment grounding conductors shall not be identified by stripping the insulation.
    2. Feeder conductors shall be installed in compliance with 250.32(B).
    Exception: For an existing feeder that is installed between the service equipment and a disconnecting means as covered in 550.32(A), it shall be permitted to omit the equipment grounding conductor where the grounded circuit conductor is grounded at the disconnecting means in accordance with 250.32(B) Exception.
  2. Feeder Capacity. Mobile home and manufactured home lot feeder circuit conductors shall have a capacity not less than the loads supplied, shall be rated at not less than 100 amperes, and shall be permitted to be sized in accordance with 310.15(B)(7).