7.5 Manufactured Homes, RV Parks, Marinas & Temporary Installations (Articles 550, 551, 555, 590)

Manufactured Homes, RV Parks, Marinas & Temporary Installations (Articles 550, 551, 555, 590)

The rest of the Special Occupancies area covers four places where power is supplied to something that moves, floats, or will soon be removed:

• mobile and manufactured homes (Article 550);
• recreational vehicles and RV parks (Article 551);
• marinas and docks (Article 555); and
• temporary construction power (Article 590).

Each article has a short list of numbers the exam likes to ask about.

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1. Mobile and Manufactured Homes (Article 550)

A mobile home is a factory-built dwelling on a permanent chassis. A manufactured home is built to the federal HUD code and may sit on a permanent foundation. Both terms are defined in Article 100.

Service equipment (550.32):

Feeder and cord (550.10, 550.33):

• A home may be supplied by a listed power-supply cord, rated 50 A maximum. A 40-A cord is allowed only when the home is factory-equipped with gas or oil heat and cooking. Cord length is 21 to 36½ feet.
• Otherwise, the home is supplied by a permanently installed feeder of four continuous, insulated, color-coded conductors: two ungrounded, one grounded (neutral), and one EGC.

Grounding inside the home (550.16). The home's panelboard is treated like a subpanel. The neutral bar is insulated from the enclosure, and the EGC bonds the frame and enclosure. The home is not the service equipment unless the 550.32(B) conditions allow it.

Park load calculations (550.31). Park electrical wiring systems are calculated at the larger of 16,000 VA per lot or the calculated load of the largest typical home the lot will accept. The demand factors of Table 550.31 decrease as the number of lots increases.

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2. Recreational Vehicles and RV Parks (Article 551)

Receptacles at each site (551.71):

Other RV park rules:

• Calculated load (551.73): Feeders and services are calculated on minimum volt-amperes per site, which differ for 50-A sites, 20- and 30-A sites, 20-A-only sites, and tent sites. Table 551.73(A) gives minimum demand factors.
• Branch circuits: Each 50-A receptacle must be on its own branch circuit (551.72).
• Grounding: EGC continuity may not depend on device removal, and there is no neutral-to-ground bonding on the load side.
• Overhead clearances (551.79): In areas subject to RV movement, overhead conductors need at least 18 ft vertically and 3 ft horizontally. Elsewhere, 225.18 and 225.19 apply.

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3. Marinas, Boatyards & Docking Facilities (Article 555)

Electric shock drowning is a real hazard: current leaking into fresh water can paralyze a swimmer. Nebraska's lakes and reservoirs make Article 555 relevant even though the state is landlocked.

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4. Temporary Installations (Article 590)

Time limits (590.3):

• During construction: Temporary power and lighting are allowed for the period of construction, remodeling, maintenance, repair, or demolition.
• 90 days: Holiday decorative lighting and similar uses are limited to 90 days.
• Emergencies and tests: Temporary wiring is allowed for emergencies, tests, experiments, and development work.
• Removal: Temporary wiring must be removed immediately when the project or purpose is complete.

Wiring rules (590.4):

• Feeders and branch circuits: They originate in an approved distribution center. Cable assemblies or multiconductor cords of hard-usage or extra-hard-usage types (Table 400.4) are allowed.
• Receptacles: All must be the grounding type. On construction sites, receptacles may not share a branch circuit with temporary lighting.
• Lamp protection: General-illumination lamps need a guard or a suitable luminaire. Metal-shell sockets must be grounded.
• Splices: On construction sites, a box is not required for splices in nonmetallic multiconductor cord or cable assemblies if EGC continuity is maintained, or for metal-sheathed cables terminated in listed fittings.
• Support: Cables and cords must be supported to protect them from damage. Branch-circuit and feeder cables may not lie on the floor or ground, and vegetation may not support overhead spans. Extension cords are exempt from the support rule.
• Disconnects: Suitable disconnects are required for every ungrounded conductor of each temporary circuit, with multiwire circuits disconnected simultaneously.

GFCI protection (590.6):

• 125-V, single-phase, 15-, 20-, and 30-A receptacle outlets that are not part of the permanent wiring and are used by personnel need listed GFCI protection.
• The 125-V and 125/250-V, 15-, 20-, and 30-A receptacles on portable generators of 15 kW or less used for temporary power also need listed GFCI protection (590.6(A)(3)).
• Other receptacles used for temporary power by personnel need GFCI protection, special-purpose GFCI (SPGFCI) protection where the voltage or phase requires it, or another method permitted by 590.6(B).
• OSHA 1926.404(b) imposes a parallel federal requirement on construction employers (section 9.3).

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5. Common Exam Traps

• Mobile home service location: The service goes beside the home, within 30 feet, not on it, unless the home is a manufactured home meeting 550.32(B).
• Mobile home feeder: It has four wires. The neutral is isolated in the home's panel.
• Temporary lighting: Construction-site receptacles may not share a circuit with temporary lighting.
• Holiday lighting: The limit is 90 days.
• Dock ground fault: Feeders and branch circuits use 100 mA GFPE. Shore power receptacles use 30 mA.