Electric Space Heating practice questions

Correct: B — Simultaneously disconnect the heater, motor controller(s), and supplementary overcurrent device(s) from all ungrounded conductors

424.19 requires a single means that simultaneously disconnects the heater, motor controller(s), and supplementary overcurrent device(s) from all ungrounded conductors — not a piecemeal or sequential disconnection, and not an exemption for any one component.

Correct: B — Subdivide the heating elements so each subdivided load does not exceed 48 amperes

424.22(B) requires that equipment rated more than 48 amperes have its resistance heating elements subdivided, with each subdivided load not exceeding 48 amperes. A single 65 A or 60 A device for the whole load doesn't satisfy the subdivision requirement, and there is no 80%-of-rating allowance in this section.

Correct: C — Only if another disconnecting means is also provided per the applicable occupancy rule

Per 424.19(C), the unit switch is permitted as the disconnecting means only where another disconnecting means is also provided, with the location of that other means varying by occupancy type in 424.19(C)(1) through (C)(4). It's not restricted to one-family dwellings only, and a locking feature isn't the qualifying condition described in this section.

Correct: A — In a closet ceiling as a low-temperature source controlling relative humidity, in the unobstructed area

424.38(C) permits heating cable in closet ceilings as a low-temperature humidity-control source, limited to the portion of the ceiling unobstructed to the floor. Built-ins with no floor clearance, tub/shower walls, and multi-run cable over ceiling-height partitions are all prohibited under 424.38(B).

Correct: D — 424.41(G)

424.41(G) sets the 13 mm (1/2 in.) maximum thickness for the surface gypsum board layer in dry board installations and requires the void beneath it to be filled with thermally conductive material. 424.41(E) covers the plaster finish thickness for plaster ceilings, and 424.41(I) governs joist spacing, not board thickness.

Correct: A — Rigid metal conduit, IMC, rigid PVC conduit, EMT, or other approved means

424.44(C) requires leads to be protected where they leave the floor by rigid metal conduit, intermediate metal conduit, rigid PVC conduit, EMT, or other approved means. Nonmetallic frames or spreaders are for securing cable during the pour (424.44(B)), not for protecting leads afterward, and flexible metal conduit isn't one of the listed methods.

Correct: B — The cable must be both GFCI protected and AFCI protected

424.48 requires heating cables and cable sets installed in, on, or behind walls to have BOTH GFCI protection (item 2) and AFCI protection (item 4), in addition to a grounding means. Neither protection type substitutes for the other, and grounding alone does not satisfy the protection requirements.

Correct: A — 150 amperes

Per 424.72(A), heating elements in an ASME-rated and stamped vessel are protected at not more than 150 amperes. The 120 A figure is the subdivision threshold, not the protection ceiling, and 60 A and 48 A are the limits that apply to non-ASME vessels under 424.72(B).

Correct: A — Not less than 125 percent of the load served by each subdivided circuit

Per 424.72(E), field-wired conductors between the heater and the supplementary OCPDs are sized at not less than 125 percent of the load served. The 100 percent option only applies to heaters rated 50 kW or more that meet the marking and cyclic-control conditions — this heater is rated 40 kW, so it doesn't qualify.

Correct: A — 424.63

424.63 (Fan Circuit Interlock) is the section requiring the fan circuit to be energized whenever any heater circuit is energized, with time/temperature delay permitted. 424.64 (Limit Controls) instead addresses automatic controls that limit maximum air temperature, not fan-heater energizing interlock, so it's a tempting but wrong distractor.

Correct: D — 424.64

424.64 requires each duct heater to have an integral, automatic-reset temperature-limiting control plus a manually resettable supplementary control. 424.63 covers fan circuit interlocking (airflow proving before energizing), 424.60 addresses elevated inlet air temperature limits, and 424.73 is the overtemperature limit control for duct heaters used with heat pumps/air conditioners under 424.61 — a different installation context.

Correct: D — At 125% of the total load, motors not included

424.82 sets the base rule at 125% of the total load, with motor loads excluded from that total. The 100% option is a separate exception (for 50 kW+ boilers or continuous-duty contactors/relays), and there's no 80% allowance in this section.

Correct: D — It must connect to an equipment grounding conductor, along with the supply and return connecting piping.

424.85 requires that when the design isolates the pressure vessel from the electrodes so fault current can't pass through it, the vessel and all exposed non-current-carrying metal parts, including supply and return piping, connect to an equipment grounding conductor. The insulated-from-ground option applies only to the other design, where the vessel isn't isolated from the electrodes.

Correct: A — The date of manufacture and serial number

424.86 requires the manufacturer's name, the volt/ampere/kilowatt rating, the electrical supply details, the "Electrode-Type Boiler" marking, and a disconnect warning. A date of manufacture or serial number is not among the listed required markings.

Correct: D — It is within sight of the heater or capable of being locked in the open position per 110.25

424.19(B)(1) permits the branch-circuit switch or breaker itself to act as the disconnect when it's within sight of the heater or lockable open per 110.25. The within-sight-of-motor-controller option applies instead to motors over 18 hp under 424.19(B)(2), and the amperage-rating and dedicated-breaker choices aren't the qualifying condition here.

Correct: B — Within sight from the fuses and on their supply side

424.19(A) requires the disconnect to be within sight from the supplementary overcurrent protective device(s) and, if those devices are fuses, on their supply side. Placing it on the load side or relying only on sight of the heater doesn't satisfy this section.

Correct: A — The supplementary overcurrent devices are field-adjustable

424.22(E) permits 100% sizing for heaters rated 50 kW or more only if the heater is marked with a minimum conductor size, the conductors meet that marked minimum, and a temperature-actuated device cycles the equipment. There's no requirement that the supplementary overcurrent devices be field-adjustable.

Correct: C — It must be rated at least 125% of the combined motor-plus-heater load

424.20(A) lists five conditions: marked 'off' position, directly opening all ungrounded conductors, no automatic re-energizing after manual 'off,' location per 424.19, and accessibility. The 125%-of-load ampere rating is a disconnect sizing rule from 424.19, not one of the five conditions that let a thermostat itself qualify as controller-and-disconnect.

Correct: D — 424.36

424.36 sets the 2 in. (50 mm) spacing for wiring above a heated ceiling and requires ampacity to be based on a 50°C ambient with 310.15(B)(1) correction. 424.39 instead covers clearance of the heating cable itself from boxes and openings, not general wiring above the ceiling.

Correct: B — GFCI protection for personnel is required in addition to whatever 210.8 already requires

424.45(E) states GFCI protection for personnel is required in addition to the requirements in 210.8 — it's a stacked requirement, not a substitute or an alternative to the grounding braid required separately under 424.45(F).

Correct: A — 424.28(A)

424.28(A) requires the nameplate to give the identifying name and normal rating in volts and watts (or volts and amperes). 424.29 governs marking of the internal heating elements, not the equipment nameplate, and 424.35 covers marking of heating cables, a different product category.

Correct: B — 424.99(B)

424.99(B) requires listed heating panels installed under floor covering to be mounted on smooth, flat surfaces per manufacturer instructions and to comply with (B)(1) through (B)(6), which bundles the expansion-joint, anchoring, and covering rules asked about. 424.99(A) only covers marking/identification of the panels, not installation requirements, and 424.98 addresses embedding heating in concrete or poured masonry, a different installation method entirely.

Correct: C — Through the unheated portions provided for that purpose

424.93(B)(3) permits nailing or stapling only through the unheated portions provided for this purpose, and prohibits penetrating current-carrying parts entirely. Staple material and distance from a joist edge are not the governing factors — proximity to the element and location relative to unheated zones are.

Correct: C — After the heating panels are installed and inspected, using a surface identified by the manufacturer's instructions as suitable

424.93(A)(4) requires the heating panels or panel sets to be installed and inspected first, and permits only a surface the manufacturer's instructions identify as suitable for that installation. Energizing the system first and using any fire-rated drywall are both wrong-rule confusions — the requirement is inspection plus manufacturer identification, not a test run or a generic fire rating.

Correct: D — As long as it is not connected to the baseboard heater circuit

Per 424.10, a factory-installed or listed separate-assembly receptacle outlet on a baseboard heater may substitute for a 210.52-required outlet, but only if it is not connected to the baseboard heater circuits. Wiring it to the heater's own circuit would violate this section, and the outlet is explicitly permitted (not prohibited) for this use.

Correct: C — A temperature-sensitive limiting means

Per 424.73, a boiler with no change of state in the heat transfer medium needs a temperature-sensitive limiting means to cap maximum liquid temperature. The pressure-sensitive option applies instead when the medium changes to vapor, per 424.74 — the wrong choice here because this boiler stays liquid.

Correct: B — Within sight from the controller

424.65 requires the disconnecting means to be installed within sight from the controller, unless another arrangement is permitted by 424.19(A). Placing it inside the duct, only at service equipment, or anywhere in the building without regard to sightline does not meet this rule.

Correct: D — Both the duct heater and the heat pump must be identified and marked as suitable for that installation

Per 424.61, when a duct heater is closer than 1.2 m (4 ft) to a heat pump or air conditioner, both pieces of equipment must be identified and marked as suitable for that specific installation — not just the heater. The 3 ft spacing is inside the 4 ft trigger distance, so the marking requirement applies.

Correct: A — Permit replacement of controls and heating elements, and allow adjusting and cleaning of controls and other parts

424.66 requires working space maintained per 110.26(A)(4) that permits replacement of controls and heating elements, and adjusting and cleaning of controls and other parts requiring attention. A doorway sightline or bare access to reset an overcurrent device doesn't meet that standard, and conductor ampacity clearance tables are unrelated to this requirement.

Correct: D — 424.57

424.57 defines the scope of Part VI, limiting it to heaters mounted in the airstream of a forced-air system where the air-moving unit is NOT integral to the equipment — since here the furnace's own blower moves the air, this is the section that determines applicability. 424.65 covers disconnect location and 424.61 covers duct heaters paired with heat pumps/AC, neither of which addresses whether Part VI applies in the first place.

Correct: A — A nameplate marking stating the heater is suitable for use at elevated inlet air temperature.

424.60 calls for identification specific to elevated inlet temperature use. A general listing without that qualifier, a current rating, or a thermostat-compatibility marking don't satisfy this requirement.

Correct: C — 424.83

424.83 covers overtemperature limit control for electrode boilers where the heat transfer medium stays liquid, requiring a temperature-sensitive device that interrupts electrode current. 424.84 is the corresponding overpressure limit control for boilers where the medium changes from liquid to vapor, and 424.82/424.85 address branch-circuit sizing and grounding, not temperature limiting.

Correct: D — Wiring methods recognized in Chapter 3

424.99(B)(2) states heating panels and panel sets shall be connected using wiring methods recognized in Chapter 3 — the general wiring methods, not a special restricted list like flexible cord or MI cable only, and not a unique low-voltage method.

Correct: B — 424.94

424.94 sets the 50 mm minimum spacing above a heated ceiling and requires ampacity to be calculated at an assumed 50°C ambient with 310.15(B)(1) correction. 424.95(B) instead governs wiring location within interior walls, and 424.93(A)(2) covers locations where heating panels themselves are not permitted, not clearance for wiring above the ceiling.

Correct: C — 424.12(B)

424.12(B) is the specific damp-or-wet-locations listing rule for heaters. 424.12(A) instead addresses physical damage exposure, and 424.6 is the general listed-equipment requirement without the location-specific wet/damp language.