Calculating lighting/small-appliance/laundry load (with demand factor)
NEC 550.18(A) Mobile home feeder loads use their own method under 550.18, not Article 220 — add lighting, small-appliance, and laundry VA, then apply 100%/35% demand factor and divide by 240.
Q1 NEC 550.18(A)
Under 550.18(A)(4), how is the total volt-ampere load assembled for a mobile home feeder calculation?
- A Lighting VA plus small-appliance VA plus laundry area VA
- B Only the single largest of the three loads, per the Article 220 optional method
- C Small-appliance VA plus laundry VA, doubled to account for both ungrounded conductors
- D Lighting VA plus small-appliance VA only, with laundry sized as a separate feeder
Show answer & explanation
Correct: A — Lighting VA plus small-appliance VA plus laundry area VA
550.18(A)(4) is a straight sum: lighting VA + small-appliance VA + laundry area VA = total volt-amperes. There's no 'largest load only' rule and no separate laundry feeder or doubling — all three pieces are added directly, then the demand factor in 550.18(A)(5) is applied to that combined total.
Mobile home main disconnecting means
NEC 550.11(A) Every mobile home gets exactly one main disconnect near the supply cord entrance, sized to the supply cord and marked "Main."
Q2 NEC 550.11(A)
In which location is the mobile home main disconnecting means panelboard NOT permitted to be installed?
- A A clothes closet
- B A hallway closet used for linens
- C A utility area near the supply cord entrance
- D A kitchen wall near the entrance
Show answer & explanation
Correct: A — A clothes closet
550.11(A) specifically bars the panelboard from a bathroom or a clothes closet. A linen closet, kitchen wall, or utility area near the cord entrance are not excluded locations, provided the equipment is otherwise readily accessible.
Total load calculation for power-supply sizing
NEC 550.18(B) Sizing a mobile home's power supply means summing lighting/small-appliance load, motor and heating/cooling load (only the larger of the two), 25% of the largest motor, appliance load (75% if more than three), and range demand from Table 550.18(B).
Q3 NEC 550.18(B)
A mobile home has both electric heating and central air conditioning installed. Per 550.18(B), how are these two loads combined into the total power-supply load?
- A Average the two nameplate loads together
- B Include only the cooling load, since it typically draws more current
- C Omit the smaller of the heating and cooling loads
- D Add both nameplate loads together in full
Show answer & explanation
Correct: C — Omit the smaller of the heating and cooling loads
Under 550.18(B)(2), the smaller of the heating and cooling loads is omitted because they don't operate at the same time. Adding both in full, keeping only cooling, or averaging them all misapply this rule.
Bonding chassis, piping, ducts & metal roof/siding
NEC 550.16(C) Every metal part of a mobile home that could become energized — chassis, pipes, ducts, metal skin — must bond back to the panelboard's grounding terminal, usually with 8 AWG copper minimum.
Q4 NEC 550.16(C)
Per 550.16(C)(1), the bonding conductor between a mobile home's panelboard and the chassis must be at minimum:
- A 8 AWG copper
- B 10 AWG copper
- C 6 AWG aluminum
- D 12 AWG copper
Show answer & explanation
Correct: A — 8 AWG copper
550.16(C)(1) and 550.16(C)(2) require the bonding conductor to be 8 AWG copper minimum (or equivalent), solid or stranded, insulated or bare. The 12 AWG and 10 AWG copper options are undersized, and 6 AWG aluminum is not the specified minimum even though it may be an equivalent size in some contexts — the rule is stated in copper terms.
Grounded (neutral) conductor insulation & range/dryer grounding
NEC 550.16(A) In a mobile home, the neutral must stay insulated from all grounded metal parts — the frame and appliance frames ground through the green equipment grounding conductor only, never the neutral.
Q5 NEC 550.16(A)
In a mobile home that is NOT using its panelboard as service equipment, where may the grounded circuit conductor terminate?
- A On a terminal bar insulated from the panelboard enclosure
- B On the same bus as the equipment grounding conductors
- C Directly on the panelboard enclosure using a bonding screw
- D On the frame of the mobile home
Show answer & explanation
Correct: A — On a terminal bar insulated from the panelboard enclosure
Per 550.16(A)(1), the grounded circuit conductor must be insulated from equipment grounding conductors and from equipment enclosures and other grounded parts, so it lands on an insulated terminal. Bonding it to the equipment grounding bus, enclosure, or frame is only allowed where the panelboard is the service equipment under 550.32(B), and even then only the neutral-to-ground bonding described there applies, not a frame connection.
Required receptacle outlet locations & spacing
NEC 550.13(D) Manufactured home wall spaces follow the 6 ft/2 ft spacing rule, plus fixed lists for kitchens, baths, laundry, and one required outdoor receptacle.
Q6 NEC 550.13(D)
In a manufactured home kitchen, when must a receptacle outlet be installed on each side of the sink?
- A When countertops exist on each side of the sink and each is 12 in. or more in width
- B Whenever the sink is centered on a wall space
- C Only if the countertop on each side exceeds 24 in. in width
- D Never — one receptacle serving both sides is always sufficient
Show answer & explanation
Correct: A — When countertops exist on each side of the sink and each is 12 in. or more in width
550.13(D)(1) requires a receptacle on each side of the sink only when countertops are present on each side and each is 300 mm (12 in.) or more wide. The 24 in. threshold and 'centered on a wall' framing don't reflect the rule, and a single shared receptacle isn't allowed when both sides qualify.
Small-appliance branch circuits (kitchen/dining)
NEC 550.12(B) Manufactured home kitchens and dining areas need at least two dedicated 20 A small-appliance circuits with no other outlets, aside from narrow exceptions for a clock and gas-range accessories.
Q7 NEC 550.12(B)
In a manufactured home, which receptacle outlet is permitted to share a 20 A small-appliance branch circuit that also serves the kitchen countertop receptacles?
- A A receptacle for a window air conditioner
- B A receptacle for a garbage disposal
- C A general lighting outlet for the dining room
- D A receptacle dedicated to an electric clock
Show answer & explanation
Correct: D — A receptacle dedicated to an electric clock
550.12(B) says small-appliance circuits shall have no other outlets, but explicitly permits a receptacle installed solely for an electric clock. A garbage disposal receptacle, a dining room lighting outlet, and a window air conditioner receptacle are not part of the listed exceptions.
Feeder Conductor Makeup & Identification
NEC 550.33(B) A mobile home feeder is either a factory-installed listed cord or four color-coded conductors marked per 310.6 — and the equipment grounding conductor can never be identified by stripping insulation.
Q8 NEC 550.33(B)
Which of the following is a permitted method of supplying feeder conductors to a mobile home under 550.33(B)?
- A A listed cord, factory installed in accordance with 550.10(B)
- B A permanently installed feeder with three insulated, color-coded conductors
- C A permanently installed feeder where the equipment grounding conductor is identified by stripping its insulation
- D A field-assembled cord not listed for the application
Show answer & explanation
Correct: A — A listed cord, factory installed in accordance with 550.10(B)
550.33(B)(1) permits either a listed cord factory installed per 550.10(B) or a permanent feeder of four insulated, color-coded conductors. The three-conductor option is wrong because four conductors are required, and stripping insulation to identify the equipment grounding conductor is explicitly prohibited.
Wiring connections to ranges, dryers & high-temp appliances
NEC 550.15(E) Ranges and dryers need 3 ft of unsupported, secured cable or flexible metal conduit — never NM or SE cable directly to the appliance — and appliances running hotter than 60°C need heat-rated conductors.
Q9 NEC 550.15(E)
An electrician is wiring a dryer with flexible metal conduit and wants to know the minimum unsupported length required to allow the appliance to be moved for service. What does 550.15(E) require?
- A 1.2 m (4 ft) of unsupported conduit, with no securing required
- B 1.8 m (6 ft) of unsupported conduit
- C 600 mm (2 ft) of unsupported conduit
- D 900 mm (3 ft) of unsupported conduit, with the conduit still secured to the wall
Show answer & explanation
Correct: D — 900 mm (3 ft) of unsupported conduit, with the conduit still secured to the wall
550.15(E) requires not less than 900 mm (3 ft) of unsupported cable or flexible metal conduit to service the appliance, and the cable or conduit must still be secured to the wall. The 1.8 m (6 ft) figure is a distractor pulled from the high-temp raceway length limit in 550.15(J), not the service loop length.
Protecting cable from physical damage (low runs & studs)
NEC 550.15(B) Exposed nonmetallic cable within 15 in. of the floor and cable passing through thin studs both need physical protection — covering, guard strips, raceway, or steel plates/tubing.
Q10 NEC 550.15(B)
In a manufactured home, exposed nonmetallic cable installed 300 mm (about 12 in.) above the floor is present. What does 550.15(B) require?
- A It must be reinstalled inside a 2 by 4 stud cavity
- B It must be protected by covering boards, guard strips, or a raceway
- C It must be replaced with metal-covered cable
- D No protection is required because it is above 300 mm
Show answer & explanation
Correct: B — It must be protected by covering boards, guard strips, or a raceway
Per 550.15(B), exposed nonmetallic cable located 380 mm (15 in.) or less above the floor must be protected by covering boards, guard strips, or raceways; 300 mm falls within that zone. The stud-passage rule and switching to metal-covered cable are unrelated remedies from 550.15(C), not requirements here.
Power-supply cord plug, length, and marking specs
NEC 550.10(C) A mobile home power-supply cord needs a 50 A, 125/250 V, 3-pole 4-wire grounding plug, an overall length between 6.4 m and 11 m, with at least 6.0 m between the plug and where it enters the home, and a marking stating its amperage.
Q11 NEC 550.10(C)
What attachment plug cap configuration is required for a mobile home power-supply cord?
- A 3-pole, 3-wire, non-grounding type, rated 40 A, 125/250 V
- B 2-pole, 3-wire, grounding type, rated 50 A, 125/250 V
- C 3-pole, 4-wire, grounding type, rated 50 A, 125/250 V
- D 3-pole, 4-wire, grounding type, rated 40 A, 125 V
Show answer & explanation
Correct: C — 3-pole, 4-wire, grounding type, rated 50 A, 125/250 V
550.10(C) requires a 3-pole, 4-wire, grounding-type plug cap rated 50 A at 125/250 V. A 2-pole, 3-wire configuration lacks the fourth conductor needed for a mobile home feeder, and ratings of 40 A or 125 V alone don't match the specified 50 A, 125/250 V rating.
Required factory electrical tests (dielectric, continuity, polarity)
NEC 550.17(A) Every mobile home must pass a 900-volt dielectric test plus continuity, operational, and polarity checks before it leaves the factory.
Q12 NEC 550.17(A)
Under 550.17(A), when must the dielectric strength test be performed on a mobile home's wiring?
- A Only after the continuity test has passed
- B Before any branch circuits are installed
- C After branch circuits are complete and luminaires or appliances are installed
- D Before the switches are closed for the first time
Show answer & explanation
Correct: C — After branch circuits are complete and luminaires or appliances are installed
550.17(A) requires the dielectric strength test to be performed after branch circuits are complete and after luminaires or appliances are installed, with all switches closed. There is no requirement that it follow a continuity test, and it cannot occur before branch circuits exist.
Feeder assembly & power-supply cord basics
NEC 550.10(A) A mobile home's feeder is either one listed 50 A power-supply cord or a permanent feeder, and any cord used must be a listed 4-conductor type with a green (or green/yellow) grounding conductor.
Q13 NEC 550.10(A)
Under what condition is a mobile home permitted to use a 40-ampere power-supply cord instead of the standard rating?
- A The local utility approves a reduced-ampacity service
- B The home has fewer than three branch circuits
- C The home is factory-equipped with gas or oil-fired central heat and cooking appliances
- D The home is single-wide rather than double-wide
Show answer & explanation
Correct: C — The home is factory-equipped with gas or oil-fired central heat and cooking appliances
Per 550.10(A), a listed 40-ampere power-supply cord is permitted only when the mobile home is factory equipped with gas or oil-fired central heating equipment and cooking appliances, which reduces electric demand. Circuit count, utility approval, and home width aren't the qualifying condition in this section.
Feeder entrance point & protection from damage/corrosion
NEC 550.10(F) A mobile home's feeder assembly must enter through the exterior wall, floor, or roof, and every exposed component needs protection from physical damage and corrosion.
Q14 NEC 550.10(F)
Per 550.10(F), where is a mobile home's feeder assembly permitted to enter the structure?
- A Through an interior partition wall for easier routing to the panelboard
- B Only through the roof, to keep it away from ground moisture
- C Only through the floor, so the entry point stays hidden from view
- D Through the exterior wall, floor, or roof
Show answer & explanation
Correct: D — Through the exterior wall, floor, or roof
550.10(F) permits the feeder assembly to enter the mobile home through the exterior wall, floor, or roof — any of the three, not just one. An interior partition wall is not an exterior surface, so it isn't an approved entrance point.
General appliance branch-circuit loading rules
NEC 550.12(D) Mixing fixed appliances with lighting caps the appliance load at 50% of circuit rating; without lighting, appliances can use the full rating but motors/continuous loads cap at 80%.
Q15 NEC 550.12(D)
In a manufactured home, a fixed water heater shares a branch circuit with general lighting outlets. Under 550.12(D), what limits the water heater's ampere rating?
- A It cannot exceed 50 percent of the branch-circuit rating
- B It must be placed on an individual branch circuit sized under Article 440
- C It cannot exceed 80 percent of the branch-circuit rating
- D It cannot exceed 100 percent of the branch-circuit rating as long as it is a continuous load
Show answer & explanation
Correct: A — It cannot exceed 50 percent of the branch-circuit rating
Per 550.12(D)(1), fixed appliances sharing a circuit with lighting outlets are limited to 50% of the circuit rating. The 80% figures apply to a lone cord-and-plug appliance or to motor/continuous loads on a circuit without lighting outlets, per 550.12(D)(2) and (3), not to this mixed-load case. Article 440 governs central air conditioning, not general fixed appliances like water heaters.
GFCI protection in mobile/manufactured homes
NEC 550.13(B) Mobile and manufactured homes follow the standard 210.8(A) dwelling GFCI rule, plus extra 125-volt 15/20 A locations like outside compartments, dishwashers, and countertop and sink receptacles.
Q16 NEC 550.13(B)
Under 550.13(B), the additional GFCI-protection requirements for mobile and manufactured homes apply to which receptacles?
- A All receptacles in the dwelling unit regardless of rating
- B Any receptacle rated 30 amperes or less regardless of voltage
- C 250-volt receptacles serving fixed appliances only
- D 125-volt, 15- and 20-ampere receptacles or outlets
Show answer & explanation
Correct: D — 125-volt, 15- and 20-ampere receptacles or outlets
550.13(B) explicitly limits the additional GFCI-required locations to 125-volt, 15- and 20-ampere receptacles or outlets. A 250-volt fixed-appliance receptacle or a blanket rule covering all receptacles goes beyond what this section requires.
Lighting branch-circuit count (VA/area method)
NEC 550.12(A) Mobile home lighting circuit count comes from a 3 VA/ft² floor-area load (coupler excluded), divided by 120 V and then by the 15- or 20-ampere circuit rating, rounded up.
Q17 NEC 550.12(A)
After calculating the total lighting amperage from the floor-area formula in 550.12(A), what determines the actual number of lighting branch circuits installed?
- A Installing a single 20-ampere circuit no matter the home's size
- B Matching the number of circuits to the mobile home's total electrical service rating
- C Dividing the calculated amperage by the chosen circuit's ampere rating (15 or 20 A)
- D Installing exactly one lighting circuit per room regardless of load
Show answer & explanation
Correct: C — Dividing the calculated amperage by the chosen circuit's ampere rating (15 or 20 A)
550.12(A) has you divide the calculated lighting current by the ampere rating chosen for the circuits (15 or 20 A) to find how many are needed. It isn't a fixed per-room count, a single fixed circuit, or tied to the service rating.
Disconnect & labeling for outside heating/AC equipment
NEC 550.20(B) A mobile home's branch circuit to outdoor heating or AC equipment must terminate in a listed outlet box or disconnect, with a labeled amperage, voltage, and ampacity, plus a disconnect within sight of the equipment.
Q18 NEC 550.20(B)
A mobile home has a branch circuit built to serve outdoor central air-conditioning equipment. Per 550.20(B), where must the branch-circuit conductors terminate?
- A In the mobile home's main service panel only
- B In a junction box inside the mobile home's utility closet
- C In a listed outlet box or disconnecting means located outside the mobile home
- D Directly spliced to the equipment's factory leads with no enclosure required
Show answer & explanation
Correct: C — In a listed outlet box or disconnecting means located outside the mobile home
550.20(B) requires the branch circuit conductors to terminate in a listed outlet box or disconnecting means on the outside of the mobile home. Terminating inside a utility closet, splicing directly to equipment leads, or stopping at the main panel does not satisfy this outdoor-termination requirement.
Pipe heating cable outlet
NEC 550.13(E) Manufactured homes need a GFCI-protected receptacle within 2 ft of the cold water inlet, on the underside of the unit, just for pipe heating cable.
Q19 NEC 550.13(E)
In a manufactured home, where must the receptacle outlet for pipe heating cable be installed?
- A In the utility compartment, within 3 ft of the water heater
- B On the underside of the unit, within 2 ft of the cold water inlet
- C Inside the crawlspace access panel, within 6 ft of the furnace
- D Anywhere on the exterior wall nearest the main disconnect
Show answer & explanation
Correct: B — On the underside of the unit, within 2 ft of the cold water inlet
550.13(E)(1) requires the outlet on the underside of the unit within 600 mm (2 ft) of the cold water inlet. The other locations aren't specified anywhere in this section.
Where receptacles are prohibited or not required
NEC 550.13(F) In manufactured homes, tub/shower zones, face-up countertops, and baseboard heaters ban receptacles outright — cabinets, swing-doors, low lattice dividers, and bar counters just don't need one.
Q20 NEC 550.13(F)
In a manufactured home, which wall space is exempt from the requirement to provide a receptacle outlet, rather than being an outright prohibited location?
- A Directly over a bathtub
- B Wall space occupied by built-in wardrobe cabinets
- C Above an electric baseboard heater without listing approval
- D Face-up in a countertop
Show answer & explanation
Correct: B — Wall space occupied by built-in wardrobe cabinets
Per 550.13(G)(1), wall space occupied by built-in kitchen or wardrobe cabinets is not required to have a receptacle — it's an exemption from spacing rules, not a ban. The bathtub space, face-up countertop position, and unlisted baseboard heater location are all outright prohibited under 550.13(F).
Service Equipment Location: Mobile vs. Manufactured Homes
NEC 550.32(A) Mobile home service equipment must always be outdoors, but manufactured homes can have it mounted in or on the unit if seven specific conditions are met.
Q21 NEC 550.32(A)
A mobile home's service equipment is being installed. Which location is code-compliant?
- A In a readily accessible outdoor location, within sight of the mobile home
- B In or on the mobile home, provided it is anchored to a permanent foundation
- C Inside a utility closet within the mobile home
- D Mounted on the exterior wall of the mobile home
Show answer & explanation
Correct: A — In a readily accessible outdoor location, within sight of the mobile home
Per 550.32(A), mobile home service equipment must be in a readily accessible outdoor location within sight of the home — it cannot be mounted in or on the mobile home. The anchoring condition belongs to manufactured homes under 550.32(B), not mobile homes.
Receptacle-Type Service Equipment: Rating & Warning Label
NEC 550.32(C) Mobile home service equipment needs at least a 100 A, 120/240 V rating, and any 125/250-volt receptacle used there requires a specific warning label right at the outlet.
Q22 NEC 550.32(C) Code lookup
You're wiring service equipment for a mobile home that will use a 125/250-volt receptacle instead of a permanent wiring connection. The receptacle configuration itself is covered elsewhere, but which section tells you what warning label must be posted next to that receptacle outlet and where it must be located?
- A 550.32(G)
- B 550.32(F)
- C 550.32(C)
- D 550.32(E)
Show answer & explanation
Correct: A — 550.32(G)
550.32(G) is the marking requirement, specifying the exact warning text about turning off the disconnect before inserting or removing the plug, and requiring it be located adjacent to the receptacle. 550.32(C) covers the ampere rating and receptacle configuration, not the label wording or placement.
Connecting Accessory Buildings to Service Equipment
NEC 550.32(D) A fixed-wiring feed to a mobile home accessory building or outside equipment must originate at the mobile home service equipment or its external disconnecting means — nowhere else.
Q23 NEC 550.32(D)
A mobile home has a detached storage building wired back to the home's electrical system with rigid conduit. Per 550.32(D), where is this fixed-wiring connection permitted to originate?
- A Only at the mobile home service equipment
- B At any readily accessible junction box in the mobile home
- C At the mobile home service equipment or the local external disconnecting means permitted in 550.32(A)
- D Only at the local external disconnecting means
Show answer & explanation
Correct: C — At the mobile home service equipment or the local external disconnecting means permitted in 550.32(A)
550.32(D) permits the connection to be made at either the mobile home service equipment or the external disconnecting means permitted under 550.32(A) — it's an either/or choice, not an exclusive requirement for just one of them, and never an arbitrary junction box.
GFCI Protection for Outdoor Receptacles at Mobile Homes
NEC 550.32(E) Any receptacle mounted outside a mobile or manufactured home needs GFCI protection, except the one that feeds power to the home itself.
Q24 NEC 550.32(E)
A receptacle mounted outside a manufactured home is used solely to supply power to the home in accordance with 550.10. Does this receptacle require GFCI protection under 550.32(E)?
- A No, because 550.32(E) exempts receptacles supplying the home under 550.10
- B Yes, because all outdoor receptacles at mobile homes require GFCI protection with no exceptions
- C Yes, but only if the supply receptacle is rated 20 amperes or less
- D No, because 550.10 receptacles are exempt from all Article 550 requirements
Show answer & explanation
Correct: A — No, because 550.32(E) exempts receptacles supplying the home under 550.10
550.32(E) explicitly states that where receptacles provide power to a mobile or manufactured home per 550.10, GFCI protection is not required. This is a specific, named exception — not a blanket exemption from Article 550, and not conditioned on amperage rating.
Outdoor Disconnect Mounting Height
NEC 550.32(F) A mobile home's outdoor disconnect must sit between 2 ft and 6 ft 7 in. above grade, measured to the enclosure bottom and to the handle's highest position.
Q25 NEC 550.32(F)
A mobile home's outdoor disconnect handle, at its highest position, is measured at 2.1 m (about 6 ft 11 in.) above finished grade. Per 550.32(F), is this compliant?
- A No, because the enclosure bottom must never exceed 2.0 m
- B Yes, because handle height has no maximum, only the enclosure bottom does
- C No, because it exceeds the 2.0 m (6 ft 7 in.) maximum handle height
- D Yes, because it exceeds the 2 ft minimum
Show answer & explanation
Correct: C — No, because it exceeds the 2.0 m (6 ft 7 in.) maximum handle height
550.32(F) caps the handle's highest position at 2.0 m (6 ft 7 in.) above grade; 2.1 m exceeds that maximum, so it's non-compliant regardless of the enclosure-bottom clearance being satisfied. The 2 ft figure is a minimum for the enclosure bottom, not a cap on the handle.
Feeder Capacity & Minimum Ampacity
NEC 550.33(C) Mobile and manufactured home feeder conductors must be sized for the actual load, but never less than 100 amperes, and can use 310.12 sizing.
Q26 NEC 550.33(C)
A manufactured home's calculated load results in a required feeder ampacity of 85 amperes. Per 550.33(C), what ampacity must the feeder conductors actually have?
- A 85 amperes, matching the calculated load
- B 100 amperes, the required minimum regardless of the lower calculated load
- C 70 amperes, using the next standard breaker size below the calculated load
- D 125 amperes, per the standard service upsizing practice
Show answer & explanation
Correct: B — 100 amperes, the required minimum regardless of the lower calculated load
550.33(C) sets 100 amperes as a hard floor for mobile/manufactured home feeder conductors, regardless of the calculated load. Even though the load calculates to only 85 A, the conductors must still provide at least 100 A of ampacity.
AFCI protection for mobile home branch circuits
NEC 550.25 Every 120V, 15- or 20-amp branch circuit feeding outlets or devices in a mobile or manufactured home needs AFCI protection under 210.12.
Q27 NEC 550.25 Code lookup
You're wiring a new manufactured home and need to determine which branch circuits require arc-fault circuit-interrupter protection. Which section sends you to the AFCI requirement for the home's 120-volt, 15- and 20-ampere branch circuits?
- A 550.32
- B 550.17
- C 550.25
- D 550.19
Show answer & explanation
Correct: C — 550.25
550.25 is the section that requires AFCI protection (via 210.12) for 120-volt, 15- and 20-ampere branch circuits in mobile and manufactured homes. 550.17 covers dielectric strength testing and 550.19 covers interconnecting multi-section units — neither addresses arc-fault protection.