Recreational Vehicles practice questions

Correct: B — 551.77(A)

551.77(A) gives the exact placement dimensions (1.5-2.1 m from the left edge, distance forward of the rear) for back-in and pull-through sites. 551.77(C) covers the access passageway, not the site-line placement, and 551.79 covers overhead conductor clearance, not equipment location on the stand.

Correct: C — No grounding electrode is required, though an auxiliary electrode per 250.54 is permitted

Per 551.76(A), RV site supply equipment that is not service equipment is not required to have a grounding electrode, though an auxiliary grounding electrode under 250.54 is permitted. The other choices invent conditions (mandatory electrode, multi-RV threshold, transformer substitution) that 551.76(A) does not impose.

Correct: C — Two ungrounded conductors, one grounded conductor, and one equipment grounding conductor

551.72(B) permits feeders from a 208Y/120-volt, 3-phase system to include two ungrounded conductors plus one grounded conductor and one equipment grounding conductor. Using three ungrounded conductors would make it a true 3-phase feed to the site, which isn't the permitted arrangement; omitting the neutral or the equipment grounding conductor also fails the rule.

Correct: C — The grounding terminals or enclosure of the panelboard

551.55(A) requires exposed metal parts to be effectively bonded to the grounding terminals or enclosure of the panelboard. Chassis-only bonding, water pipe bonding, or a separate site electrode are not what this section specifies for interior equipment grounding.

Correct: B — 600 volt-amperes per site

Per 551.73(A)(4), sites with only 20-ampere supply facilities dedicated to tent sites use 600 VA per site. The 2400 VA figure applies to general 20-ampere-only sites that aren't tent-dedicated, per 551.73(A)(3).

Correct: C — A main disconnecting means must be provided

551.45(C) requires a main disconnecting means whenever fuses are used, regardless of the branch circuit count. The dead-front requirement applies to the panelboard overall, not conditionally based on circuit count, and fuses do not need to be swapped for breakers.

Correct: D — A receptacle in a dedicated space for a built-in freezer

551.41(C) exempts receptacles installed for appliances in dedicated spaces such as disposals, refrigerators, and freezers. The lavatory-adjacent, exterior, and shower-area receptacles are three of the five locations explicitly requiring GFCI protection.

Correct: C — A 125-volt, 20-ampere receptacle

Per 551.71(F)(2), GFCI protection in RV site equipment is required only for 125-volt, single-phase, 15- and 20-ampere receptacles. The 30-ampere and 50-ampere RV receptacles are excluded because RV appliances can produce leakage current exceeding a Class A GFCI's trip threshold, which would cause nuisance tripping.

Correct: C — 20-ampere, 125-volt weather-resistant receptacle

551.71(A) requires at least one 20-ampere, 125-volt weather-resistant receptacle at every site. The 30-ampere and 50-ampere options are additional requirements that apply only to a percentage of sites, not every site, and the 20-ampere receptacle is specifically exempted from the tamper-resistant requirement rather than required to have it.

Correct: A — The chassis is a unitized metal frame securely bolted, welded, or riveted to the panelboard

551.56(B) says a unitized metal chassis-frame construction securely fastened to the panelboard by bolts and nuts, welding, or riveting is considered bonded, so no separate conductor is required. Proximity, coatings, or usage pattern aren't recognized substitutes under this section.

Correct: A — Both the panel overlap/fastener condition and the lower-panel-to-chassis connection are satisfied together

551.56(D) requires both conditions to apply: panels overlapping with metal fasteners AND the lower panel secured to the chassis at each cross member (or strapped to it). Satisfying only the panel-overlap condition or only the chassis-connection condition is not sufficient on its own.

Correct: B — 551.47(D)

551.47(D) requires boxes in combustible walls or ceilings to be flush with or project from the finished surface. 551.47(C) only addresses nonmetallic box compatibility with wiring methods, and 551.47(E) addresses mounting methods, not surface flushness.

Correct: D — Up to 150% of the appliance's rating

551.43(A)(2) permits overcurrent protection up to 150% of the rating of a single appliance rated 13.3 amperes or more on an individual branch circuit. The 125% figure is a common continuous-load rule from elsewhere in the NEC but isn't the figure this section sets, and 100% or 200% aren't the permitted values here.

Correct: D — 551.47(I)

551.47(I) sets the 1.4 m (4 1/2 ft) maximum support interval for cables secured with connectors or clamps, plus the 300 mm (12 in.) rule near boxes. 551.47(J) is a different rule that applies only to nonmetallic-sheathed cable at nonmetallic boxes lacking cable clamps, with its own 200 mm (8 in.) distance.

Correct: B — Conduit or raceway identified for wet locations, with conductors listed for wet locations

551.47(N)(1) requires exposed outdoor or under-chassis line-voltage wiring (120V nominal or higher) to be protected by wet-location-identified conduit or raceway, with wet-location-listed conductors. Guard strips address physical damage under 551.47(K)/(N)(2), and the steel tube spec is for stud penetrations under 551.47(G), not moisture exposure.

Correct: A — The receptacle must be GFCI-protected for personnel and listed for wet locations

Per 551.47(P)(1)(b), an exterior-located receptacle for the cord connection must be protected with a GFCI for personnel and be listed for wet locations. GFCI protection cannot be substituted with just a wet-location listing or an in-use cover, and AFCI is not the requirement specified here.

Correct: A — Metal faceplates must comply with 406.6(A) and be grounded per 404.9(B) and 404.6(B); nonmetallic faceplates need only meet 406.6(C).

551.47(L) splits the rule by material: metal faceplates comply with 406.6(A), nonmetallic with 406.6(C). 551.47(M) adds a grounding duty only for metal faceplates, citing 404.9(B) and 404.6(B) — it doesn't apply to nonmetallic ones, and Article 551 doesn't replace Article 406, it cross-references it.

Correct: B — 1080 volts ac or 1530 volts dc

Per 551.60, the 1-second dielectric test uses 1080 volts ac or 1530 volts dc. The 900 volts ac / 1280 volts dc figures belong to the longer 1-minute version of the same test, not the 1-second one.

Correct: C — The generator and an outside power source both being connected to a vehicle circuit at the same time

551.30(B) requires equipment to ensure the current-carrying conductors from the generator and from an outside source are never connected to a vehicle circuit simultaneously, preventing a dangerous backfeed condition. Duty cycle, frequency, and fuel tank clearance aren't addressed by this section.

Correct: C — 551.30(E)

551.30(E) covers the supply conductors themselves — stranded conductor type, required flexible/liquidtight conduit, and the five acceptable points of first termination. 551.30(A) addresses generator mounting and 551.30(B) covers overcurrent protection for the generator, neither of which govern the supply conductor wiring method.

Correct: C — If the sixth circuit serves only the power converter and total load stays within the original five-circuit design

Per 551.42(C), a sixth circuit is allowed without an energy management system only if it serves solely the power converter and the combined load of all six circuits doesn't exceed what the original five circuits were designed for. Restricting the sixth circuit to lighting, upgrading to a 40-ampere panelboard, or adding isolation switching to the existing five circuits are not the exception described in the section.

Correct: A — By one 30-ampere or one 50-ampere external power supply cord only

551.72(F) requires each recreational vehicle to be powered by only one 30-ampere or one 50-ampere external power supply cord — not a combination, and not a second cord for specific loads. The informational note clarifies the 15/20-ampere convenience receptacle on the RV supply equipment is still allowed, but it doesn't substitute for the single rated supply cord.

Correct: D — Remove and discard the bonding screw

Per 551.54(C), bonding screws, straps, or buses in the panelboard or in appliances shall be removed and discarded, because the RV panelboard is not a service — the neutral-ground bond exists only at the shore supply. Treating it like a service panel or reinforcing the bond creates an improper parallel neutral-ground path.

Correct: B — One dimension of working clearance may be reduced to 550 mm (22 in.)

Per 551.45(B), a panelboard is considered exposed when its cover is within 50 mm (2 in.) of the aisle's finished surface, which is the case here at 40 mm. That allows only one of the two working clearance dimensions to be reduced to 550 mm (22 in.) — not both, and not a blanket exemption from clearance.

Correct: A — From the point of entrance on the vehicle exterior to the face of the attachment plug at the supply end

551.46(B) defines usable length as measured from the point of entrance to the vehicle (or the flanged surface inlet face) to the face of the attachment plug at the supply end. Measuring from an interior panelboard, a receptacle, or relying on a manufactured length label doesn't reflect the actual usable reach of the cord.

Correct: A — On the exterior skin, at or near the power-supply cord entrance point

551.46(D) requires the label be affixed to the exterior skin, at or near the point of entrance of the power-supply cord(s). The panel cover, data plate location, and cord storage compartment are not the specified placement under this section.

Correct: C — Within 15 ft of the rear, on the left (road) side, within 18 in. of the outside wall

551.46(E) sets the default entrance point within 4.5 m (15 ft) of the rear, on the left (road) side, within 450 mm (18 in.) of the outside wall. The front-right option and the 10 ft/either-side option reverse or shrink these specific dimensions.

Correct: C — The overcurrent protective device is installed and wired in the panelboard even though no air conditioner is connected yet

551.47(Q)(1) requires the overcurrent protective device to be installed in the panelboard with wiring connections completed, even before the air conditioner exists. The circuit must serve no other purpose per 551.47(Q)(4), free conductor ends must be capped or taped per 551.47(Q)(2), and the marked rating cannot exceed 80% of the circuit rating per 551.47(Q)(3).

Correct: D — 551.41(A)

551.41(A) sets the 1.8 m (6 ft) spacing rule so no point on a qualifying wall space is more than 6 ft from an outlet. 551.41(B) instead lists specific required locations like countertops and the refrigerator space, which is a different requirement than general spacing.

Correct: D — When the switch is installed as part of a listed tub or shower assembly

551.51(B) allows a switch in the wet location of a tub or shower space only when it's installed as part of a listed tub or shower assembly — the assembly itself is tested and certified as a unit. A wet-location-rated switch alone doesn't meet this, GFCI protection addresses shock risk but not the location restriction, and there's no exception based on wall placement relative to the showerhead. See 551.51(B).

Correct: B — It must be insulated and identified for the use, the same as any other direct-burial conductor

551.80(A) specifically calls out that the equipment grounding conductor, if aluminum, must be insulated and identified for the use — closing off the common assumption that grounding conductors can be bare underground.

Correct: A — 30 amperes

551.31(D) allows the external feeder assembly to be sized below the calculated load, but never less than 30 amperes. 20 A and 15 A fall below that floor, and the section explicitly permits going under the calculated load, so matching the full 42 A figure isn't required.

Correct: C — That shore power and an alternate ac source are never connected to the vehicle circuit at the same time

551.33 requires transfer equipment to ensure that current-carrying conductors from another ac source and from an outside source are not connected to the vehicle circuit at the same time. Allowing both sources to feed the circuit together, or sequencing generator start-up, does not address the core hazard this section targets; GFCI protection is a separate requirement not covered here.

Correct: C — 551.55(F)

551.55(F) specifically addresses cord-connected appliances like washing machines and clothes dryers, requiring an approved cord with equipment grounding conductor and grounding-type attachment plug. 551.55(A) covers exposed metal parts generally, and 551.54(A) covers power-supply grounding for the RV's electrical system, not individual cord-connected appliances.

Correct: D — Because the plug is rated 125/250 volts and must carry both ungrounded conductors plus a neutral and equipment ground

551.46(C)(4) specifies a 3-pole, 4-wire grounding-type plug rated 50 A, 125/250 V because that supply provides two ungrounded conductors, a grounded (neutral) conductor, and an equipment grounding conductor — the 125/250 V dual-voltage supply is what drives the extra pole and wire, not amperage alone or a blanket NEMA rule.

Correct: C — When the entire wiring system and equipment are rated and installed in full conformity with the 120-volt requirements of Parts I through V of Article 551

551.20(A) permits connecting dc vehicle wiring to a 120-volt source only if the entire wiring system and equipment conform fully to Parts I–V of Article 551 covering 120-volt electrical systems. Separate compartments, a higher DC voltage rating, or electrician sign-off are not the conditions the rule sets — the requirement is full conformity of the whole system to the 120-volt rules.

Correct: D — 8 AWG copper

551.20(C) requires a minimum 8 AWG copper conductor to bond the voltage converter's non-current-carrying metal enclosure to the vehicle frame. The 10 AWG and 12 AWG copper options are undersized, and the rule specifies copper, not aluminum.