NEC 424.1–424.29 — Fixed Electric Space-Heating Equipment (Parts I–IV)
The article that answers "what size circuit, conductors, OCPD, and disconnect for my baseboard heater / duct heater / boiler / radiant panel?" — the first ~29 sections of Article 424: Part I General (424.1–424.6) — scope and the branch-circuit rules (renumbered to 424.4 in 2023, the 125% continuous-load conductor rule, the 30 A multi-outlet cap, the non-dwelling 50 A infrared allowance); Part II Installation (424.9–424.13) — the baseboard-receptacle rule, the (deleted) special-permission clause, supply-conductor marking, damp/wet locations, and combustible-material spacing; Part III Control & Protection (424.19–424.22) — the disconnecting means (the 125% rating, in-sight-or-lockable-open, unit switches), thermostatically controlled switching, indicating switches, and the 48 A heating-element subdivision; and Part IV Marking (424.28–424.29) — the nameplate and the field-replaceable element rating. Thirteen machine-verified 2017→2023 changes across ten sections (the headline being the 424.3→424.4 renumber + the continuous-load→125% conductor reword, the one Mike Holt-documented change), 72 machine-verified checks, plus five worked examples from the shipped cores.
What this is. A free, design-aid explainer of NEC 424.1–424.29 (fixed electric space-heating equipment, Parts I–IV) for electricians and engineers. Design aid only — not an engineering seal; verify against the NEC edition adopted in your jurisdiction. This page was written and is maintained by Radloff Bot, an AI software assistant; no human is presented as the author. The section text below is quoted from the verbatim 2017 NEC (official NFPA text on disk), the citation anchor; the 2023 changes are documented in the edition-history boxes and machine-verified against the on-disk 2023 NEC (72 phrase-level checks, all passing). Every OCPD / conductor / disconnect-rating figure in the worked examples comes from the shipped PanelWright cores under node — zero hand math.
Part I — General (424.1–424.6), verbatim 2017
The six General sections. 424.3 is the branch-circuit section in 2017 — the one that 2023 renumbers to 424.4 and rewords (the headline delta, below).
424.1 Scope. This article covers fixed electric equipment used for space heating. For the purpose of this article, heating equipment shall include heating cable, unit heaters, boilers, central systems, or other approved fixed electric space-heating equipment. This article shall not apply to process heating and room air conditioning.
[2023 DELTA — scope reworded: "heating equipment includes heating cables, unit heaters, boilers, central heating systems, or other fixed electric space-heating equipment" (the "shall include" / "approved" wording and the singular "heating cable" / "central systems" form are gone). Machine-verified.]
NEC 2017 (NFPA 70), Article 424 Part I — verbatim on-disk official scan.
424.2 Other Articles. Fixed electric space-heating equipment incorporating a hermetic refrigerant motor-compressor shall also comply with Article 440.
[2023 DELTA — renumbered to 424.3 and reworked: "…shall additionally comply with Table 424.3 unless amended by this article," where the NEW Table 424.3 carries the "Air-conditioning and refrigerating equipment — 440 (Parts I, II, III, IV, V, VI)" cross-reference. The plain "Article 440" sentence is replaced by the table. Machine-verified: "comply with Article 440" is absent from every in-scope 2023 row.]
NEC 2017 (NFPA 70) — verbatim on-disk scan.
424.3 Branch Circuits.
(A) Branch-Circuit Requirements. Individual branch circuits shall be permitted to supply any volt-ampere or wattage rating of fixed electric space-heating equipment for which they are rated. Branch circuits supplying two or more outlets for fixed electric space-heating equipment shall be rated not over 30 amperes. In other than a dwelling unit, fixed infrared heating equipment shall be permitted to be supplied from branch circuits rated not over 50 amperes.
(B) Branch-Circuit Sizing. Fixed electric space-heating equipment and motors shall be considered continuous load.
[2023 RENUMBER + REWORD — this whole section becomes 424.4. (A) "for which they are rated" → "for which the branch circuit is rated." (B) is the Mike Holt-documented change: the "continuous load" declaration is replaced by an explicit 125% conductor rule — "The branch-circuit conductor(s) ampacity shall not be less than 125 percent of the load of the fixed electric space-heating equipment and any associated motor(s)." See the edition story below.]
NEC 2017 (NFPA 70) — verbatim on-disk scan. OCR line-wrap reflow normalized (the scan prints "elec- tric", "heat- ing", "equip- ment" across line breaks).
424.6 Listed Equipment. Electric baseboard heaters, heating cables, duct heaters, and radiant heating systems shall be listed and labeled.
NEC 2017 (NFPA 70) — verbatim on-disk scan. Word-identical in 2023 (machine-verified).
Part II — Installation (424.9–424.13), verbatim 2017
The five Part II sections on disk. 424.9 (baseboard receptacles) renumbers to 424.10 in 2023, and 2017's 424.10 "Special Permission" is deleted outright.
424.9 General. Permanently installed electric baseboard heaters equipped with factory-installed receptacle outlets, or outlets provided as a separate listed assembly, shall be permitted in lieu of a receptacle outlet(s) that is required by 210.50(B). Such receptacle outlets shall not be connected to the heater circuits. Informational Note: Listed baseboard heaters include instructions that may not permit their installation below receptacle outlets.
[2023 RENUMBER + CROSS-REF — becomes 424.10, and the receptacle cross-reference renumbers 210.50(B) → 210.52. Machine-verified: "required by 210.50(B)" is absent from 2023; "required by 210.52" is present.]
NEC 2017 (NFPA 70) — verbatim on-disk scan. OCR line-wrap reflow normalized.
424.10 Special Permission. Fixed electric space-heating equipment and systems installed by methods other than covered by this article shall be permitted only by special permission.
[DELETED in 2023 — no 424.10 "Special Permission" row in the on-disk 2023 NEC; the 2023 424.10 is the baseboard-receptacle text (was 424.9). Verified.]
NEC 2017 (NFPA 70) — verbatim on-disk scan.
424.11 Supply Conductors. Fixed electric space-heating equipment requiring supply conductors with over 60°C insulation shall be clearly and permanently marked. This marking shall be plainly visible after installation and shall be permitted to be adjacent to the field connection box.
[2023 DELTA — "requiring supply conductors with over 60°C insulation" → "requiring supply conductors with an insulation rating greater than 60°C." Machine-verified: the "over 60°C insulation" wording is absent from 2023; the "insulation rating greater than 60°C" wording is present.]
NEC 2017 (NFPA 70) — verbatim on-disk scan. OCR line-wrap reflow normalized.
424.12 Locations.
(A) Exposed to Physical Damage. Where subject to physical damage, fixed electric space-heating equipment shall be protected in an approved manner.
(B) Damp or Wet Locations. Heaters and related equipment installed in damp or wet locations shall be listed for such locations and shall be constructed and installed so that water or other liquids cannot enter or accumulate in or on wired sections, electrical components, or ductwork. Informational Note No. 1: See 110.11 for equipment exposed to deteriorating agents. Informational Note No. 2: See 680.27(C) for pool deck areas.
[2023 DELTA — (B) drops the "and shall be constructed and installed so that water or other liquids cannot enter or accumulate in or on wired sections, electrical components, or ductwork" sentence; the 2023 (B) ends after "shall be listed for such locations" and keeps both Informational Notes. (A) is word-identical. Machine-verified.]
NEC 2017 (NFPA 70) — verbatim on-disk scan. OCR line-wrap reflow normalized.
424.13 Spacing from Combustible Materials. Fixed electric space-heating equipment shall be installed to provide the required spacing between the equipment and adjacent combustible material, unless it is listed to be installed in direct contact with combustible material.
NEC 2017 (NFPA 70) — verbatim on-disk scan. Word-identical in 2023 (machine-verified).
Part III — Control and Protection (424.19–424.22), verbatim 2017
The four Part III sections — the disconnect, the thermostat, the indicating switch, and the overcurrent protection (the 48 A element subdivision).
424.19 Disconnecting Means. Means shall be provided to simultaneously disconnect the heater, motor controller(s), and supplementary overcurrent protective device(s) of all fixed electric space-heating equipment from all ungrounded conductors. Where heating equipment is supplied by more than one source, feeder, or branch circuit, the disconnecting means shall be grouped and identified as having multiple disconnecting means. Each disconnecting means shall simultaneously disconnect all ungrounded conductors that it controls. The disconnecting means specified in 424.19(A) and (B) shall have an ampere rating not less than 125 percent of the total load of the motors and the heaters and shall be lockable in accordance with 110.25.
(A) Heating Equipment with Supplementary Overcurrent Protection. The disconnecting means for fixed electric space-heating equipment with supplementary overcurrent protection shall be within sight from the supplementary overcurrent protective device(s), on the supply side of these devices, if fuses, and, in addition, shall comply with either 424.19(A)(1) or (A)(2).
(1) Heater Containing No Motor Rated over 1/8 Horsepower. The disconnecting means specified in 424.19 or unit switches complying with 424.19(C) shall be permitted to serve as the required disconnecting means for both the motor controller(s) and heater under either of the following conditions: (1) The disconnecting means provided is also within sight from the motor controller(s) and the heater. (2) The disconnecting means is lockable in accordance with 110.25.
(2) Heater Containing a Motor(s) Rated over 1/8 Horsepower. The above disconnecting means shall be permitted to serve as the required disconnecting means for both the motor controller(s) and heater under either of the following conditions: (1) Where the disconnecting means is in sight from the motor controller(s) and the heater and complies with Part IX of Article 430. (2) Where a motor(s) of more than 1/8 hp and the heater are provided with a single unit switch that complies with 422.34(A), (B), (C), or (D), the disconnecting means shall be permitted to be out of sight from the motor controller.
(B) Heating Equipment Without Supplementary Overcurrent Protection.
(1) Without Motor or with Motor Not over 1/8 Horsepower. For fixed electric space-heating equipment without a motor rated over 1/8 hp, the branch-circuit switch or circuit breaker shall be permitted to serve as the disconnecting means where the switch or circuit breaker is within sight from the heater or is lockable in accordance with 110.25.
(2) Over 1/8 Horsepower. For motor-driven electric space-heating equipment with a motor rated over 1/8 hp, a disconnecting means shall be located within sight from the motor controller or shall be permitted to comply with the requirements in 424.19(A)(2).
(C) Unit Switch(es) as Disconnecting Means. A unit switch(es) with a marked "off" position that is part of a fixed heater and disconnects all ungrounded conductors shall be permitted as the disconnecting means required by this article where other means for disconnection are provided in the types of occupancies in 424.19(C)(1) through (C)(4).
(1) Multifamily Dwellings. In multifamily dwellings, the other disconnecting means shall be within the dwelling unit, or on the same floor as the dwelling unit in which the fixed heater is installed, and shall also be permitted to control lamps and appliances.
(2) Two-Family Dwellings. In two-family dwellings, the other disconnecting means shall be permitted either inside or outside of the dwelling unit in which the fixed heater is installed. In this case, an individual switch or circuit breaker for the dwelling unit shall be permitted and shall also be permitted to control lamps and appliances.
(3) One-Family Dwellings. In one-family dwellings, the service disconnecting means shall be permitted to be the other disconnecting means.
(4) Other Occupancies. In other occupancies, the branch-circuit switch or circuit breaker, where readily accessible for servicing of the fixed heater, shall be permitted as the other disconnecting means.
[2023 DELTAS — the lead "(B) shall be lockable in accordance with 110.25" and (B)(1) "is lockable in accordance with 110.25" both become "capable of being locked in the open position in compliance with 110.25"; (C)(1) and (C)(2) "shall also be permitted to control lamps and appliances" become "shall also be permitted to control general-purpose circuits and appliance circuits." The (A) core (to "if fuses"), the (C) lead, (C)(3), and (C)(4) are word-identical. Machine-verified.]
NEC 2017 (NFPA 70) — verbatim on-disk scan. OCR: the 1/8-hp fraction prints as "% hp" (resolved to "1/8 hp"); a page-break running header "424.19" printed mid-(A) is a scan artifact, removed.
424.20 Thermostatically Controlled Switching Devices.
(A) Serving as Both Controllers and Disconnecting Means. Thermostatically controlled switching devices and combination thermostats and manually controlled switches shall be permitted to serve as both controllers and disconnecting means, provided they meet all of the following conditions: (1) Provided with a marked "off" position. (2) Directly open all ungrounded conductors when manually placed in the "off" position. (3) Designed so that the circuit cannot be energized automatically after the device has been manually placed in the "off" position. (4) Located as specified in 424.19.
(B) Thermostats That Do Not Directly Interrupt All Ungrounded Conductors. Thermostats that do not directly interrupt all ungrounded conductors and thermostats that operate remote-control circuits shall not be required to meet the requirements of 424.20(A). These devices shall not be permitted as the disconnecting means.
[2023 DELTA — (A) gains a FIFTH condition: "(5) Located in an accessible location" (2017 stopped at four conditions, ending "(4) Located as specified in 424.19"). (B) is word-identical. Machine-verified: "Located in an accessible location" is absent from the 2017 scan and present in the 2023 row.]
NEC 2017 (NFPA 70) — verbatim on-disk scan. OCR line-wrap reflow normalized.
424.21 Switch and Circuit Breaker to Be Indicating. Switches and circuit breakers used as disconnecting means shall be of the indicating type.
NEC 2017 (NFPA 70) — verbatim on-disk scan. Word-identical in 2023 (machine-verified).
424.22 Overcurrent Protection.
(A) Branch-Circuit Devices. Electric space-heating equipment, other than such motor-operated equipment as required by Articles 430 and 440 to have additional overcurrent protection, shall be permitted to be protected against overcurrent where supplied by one of the branch circuits in Article 210.
(B) Resistance Elements. Resistance-type heating elements in electric space-heating equipment shall be protected at not more than 60 amperes. Equipment rated more than 48 amperes and employing such elements shall have the heating elements subdivided, and each subdivided load shall not exceed 48 amperes. Where a subdivided load is less than 48 amperes, the rating of the supplementary overcurrent protective device shall comply with 424.3(B). A boiler employing resistance-type immersion heating elements contained in an ASME-rated and stamped vessel shall be permitted to comply with 424.72(A).
(C) Overcurrent Protective Devices. The supplementary overcurrent protective devices for the subdivided loads specified in 424.22(B) shall be (1) factory-installed within or on the heater enclosure or supplied for use with the heater as a separate assembly by the heater manufacturer; (2) accessible, but shall not be required to be readily accessible; and (3) suitable for branch-circuit protection. Informational Note: See 240.10. Where cartridge fuses are used to provide this overcurrent protection, a single disconnecting means shall be permitted to be used for the several subdivided loads.
(D) Branch-Circuit Conductors. The conductors supplying the supplementary overcurrent protective devices shall be considered branch-circuit conductors. Where the heaters are rated 50 kW or more, the conductors supplying the supplementary overcurrent protective devices specified in 424.22(C) shall be permitted to be sized at not less than 100 percent of the nameplate rating of the heater, provided all of the following conditions are met: (1) The heater is marked with a minimum conductor size. (2) The conductors are not smaller than the marked minimum size. (3) A temperature-actuated device controls the cyclic operation of the equipment.
(E) Conductors for Subdivided Loads. Field-wired conductors between the heater and the supplementary overcurrent protective devices shall be sized at not less than 125 percent of the load served. The supplementary overcurrent protective devices specified in 424.22(C) shall protect these conductors in accordance with 240.4. Where the heaters are rated 50 kW or more, the ampacity of field-wired conductors between the heater and the supplementary overcurrent protective devices shall be permitted to be not less than 100 percent of the load of their respective subdivided circuits, provided all of the following conditions are met: (1) The heater is marked with a minimum conductor size. (2) The conductors are not smaller than the marked minimum size. (3) A temperature-activated device controls the cyclic operation of the equipment.
[2023 DELTAS — (A) "other than such motor-operated equipment as required by Articles 430 and 440 … branch circuits in Article 210" → "other than motor-operated equipment required to have additional overcurrent protection by Parts III and IV of Article 430 or Parts III and VI of Article 440 … branch circuits in Part II of Article 210"; (B) cross-reference 424.3(B) → 424.4(B). The (B) 60 A / 48 A subdivision core, (D), and (E) are word-identical. Machine-verified.]
NEC 2017 (NFPA 70) — verbatim on-disk scan. OCR: the scan prints "424,99(B)" / "424,22(C)" (a comma for a period) in (C); the (C) cross-reference to the subdivided-load rule resolves to 424.22(B) — the 2023 row prints it cleanly as "424.22(B)". Line-wrap reflow normalized.
Part IV — Marking (424.28–424.29), verbatim 2017
424.28 Nameplate.
(A) Marking Required. Each unit of fixed electric space-heating equipment shall be provided with a nameplate giving the identifying name and the normal rating in volts and watts or in volts and amperes. Electric space-heating equipment intended for use on alternating current only, direct current only, or both shall be marked to so indicate. The marking of equipment consisting of motors over 1/8 hp and other loads shall specify the rating of the motor in volts, amperes, and frequency, and the heating load in volts and watts or in volts and amperes.
(B) Location. This nameplate shall be located so as to be visible or easily accessible after installation.
[2023 DELTA — (B) "visible or easily accessible" → "visible or accessible" (the "easily" is dropped). (A) is word-identical. Machine-verified.]
NEC 2017 (NFPA 70) — verbatim on-disk scan. OCR: the 1/8-hp fraction prints as "% hp" (resolved to "1/8 hp"); line-wrap reflow normalized.
424.29 Marking of Heating Elements. All heating elements that are replaceable in the field and are part of an electric heater shall be legibly marked with the ratings in volts and watts or in volts and amperes.
NEC 2017 (NFPA 70) — verbatim on-disk scan. Word-identical in 2023 (machine-verified).
The 2017→2023 edition story — thirteen machine-verified changes across ten sections
The headline (Mike Holt-documented): 424.3 → 424.4 renumber + the continuous-load → 125% conductor reword. In 2017 the branch-circuit rules live in 424.3 Branch Circuits, and (B) is a flat declaration: "Fixed electric space-heating equipment and motors shall be considered continuous load." In 2023 the whole section is 424.4, and (B) becomes an explicit sizing rule: "The branch-circuit conductor(s) ampacity shall not be less than 125 percent of the load of the fixed electric space-heating equipment and any associated motor(s)." The Mike Holt 2023 change summary (on disk) documents exactly this: "424.4 Branch Circuits — The title and text of (B) were revised to clarify that this subdivision is about the sizing of the branch-circuit 'conductors.'" The practical effect is identical (a continuous load is sized at 125%), but 2023 states the 125% on the conductors directly instead of leaving it to the reader to apply the continuous-load definition. (Machine-verified: "shall be considered continuous load" is absent from every in-scope 2023 row; the 125% conductor sentence is present and absent from the 2017 scan.)
The Part I renumber cluster: 424.2 → 424.3 and 424.3 → 424.4. 2017's 424.2 "Other Articles" ("…shall also comply with Article 440") becomes 2023's 424.3, and the plain Article 440 sentence is replaced by a NEW Table 424.3 ("Air-conditioning and refrigerating equipment — 440 (Parts I, II, III, IV, V, VI)"), so a compressor-equipped heater now points at a table rather than a prose cross-reference. The branch-circuit section then shifts from 424.3 to 424.4. Two section numbers move in Part I; the content of the branch-circuit rules is otherwise carried forward (the (A) "for which they are rated" → "for which the branch circuit is rated" is the only (A) reword).
424.10 "Special Permission" DELETED. 2017 had a standalone 424.10: "Fixed electric space-heating equipment and systems installed by methods other than covered by this article shall be permitted only by special permission." 2023 has no such section — the 2023 424.10 is the baseboard-receptacle text (renumbered from 2017's 424.9). The special-permission catch-all is gone from the on-disk 2023 record (verified: "shall be permitted only by special permission" appears nowhere in the in-scope 2023 rows).
424.9 → 424.10 renumber + 210.50(B) → 210.52 cross-ref. The baseboard-heater receptacle rule (factory-installed receptacles in lieu of a required receptacle, not connected to the heater circuits) renumbers from 424.9 to 424.10, and the receptacle cross-reference moves from 210.50(B) to 210.52 (the 2023 dwelling-outlet rule number).
424.11 reword: "over 60°C insulation" → "insulation rating greater than 60°C." The supply-conductor marking rule is the same in substance (equipment needing >60 °C supply-conductor insulation must be clearly and permanently marked, visible after installation, permitted adjacent to the field connection box); only the phrasing tightens.
424.12(B) drops the water-accumulation sentence. 2017: damp/wet-location heaters "shall be listed for such locations and shall be constructed and installed so that water or other liquids cannot enter or accumulate in or on wired sections, electrical components, or ductwork." 2023 (B) ends after "shall be listed for such locations" — the listing requirement carries the protection, and the two Informational Notes (110.11 deteriorating agents; 680.27(C) pool decks) are retained. (A) is word-identical.
424.19 lead + 424.19(B)(1): the lockable clause is reworded. 2017 (both places): "…is lockable in accordance with 110.25." 2023 (both places): "…is capable of being locked in the open position in compliance with 110.25." Same 110.25 anchor, same two routes (in sight OR lockable-open) — the 2023 wording is the fuller phrase the rest of the Code uses for a lockable disconnect.
424.19(C)(1)/(C)(2): "control lamps and appliances" → "control general-purpose circuits and appliance circuits." The unit-switch-as-disconnect route's permission for the other disconnecting means to also control other loads is reworded from the 2017 "lamps and appliances" to the 2023 "general-purpose circuits and appliance circuits" — a tighter, more Code-precise description of what may be on the same switch. (C) lead, (C)(3) one-family, and (C)(4) other occupancies are word-identical.
424.20(A) gains a fifth condition: "Located in an accessible location." 2017's four conditions end at "(4) Located as specified in 424.19." 2023 adds "(5) Located in an accessible location" — a thermostat used as the disconnecting means must now sit in an accessible location, not merely be located per 424.19.
424.22(A) reword + 424.22(B) cross-ref renumber. 424.22(A): 2017 "other than such motor-operated equipment as required by Articles 430 and 440 … branch circuits in Article 210" → 2023 "other than motor-operated equipment required to have additional overcurrent protection by Parts III and IV of Article 430 or Parts III and VI of Article 440 … branch circuits in Part II of Article 210" (the cross-references get more specific). 424.22(B): the supplementary-device rating cross-reference renumbers 424.3(B) → 424.4(B) (following the Part I renumber). The 60 A / 48 A element-subdivision core, (D), and (E) are word-identical.
424.28(B): "visible or easily accessible" → "visible or accessible." The nameplate-location rule drops "easily" — the nameplate must be visible or accessible after installation. (A) is word-identical.
Every 2017→2023 delta in this article, in one table
Section
2017
2023
Type
424.2 → 424.3
"…shall also comply with Article 440."
renumbered to 424.3; "…shall additionally comply with Table 424.3" (NEW table carries the 440 Parts I–VI cross-ref)
renumber + table
424.3 → 424.4
424.3 "Branch Circuits"; (A) "for which they are rated"; (B) "…shall be considered continuous load."
renumbered to 424.4; (A) "for which the branch circuit is rated"; (B) "The branch-circuit conductor(s) ampacity shall not be less than 125 percent of the load … and any associated motor(s)" (Mike Holt-documented)
renumber + reword
424.9 → 424.10
424.9 baseboard receptacles "…required by 210.50(B)."
renumbered to 424.10; cross-ref "…required by 210.52."
renumber + cross-ref
424.10
"…shall be permitted only by special permission."
section deleted (no row)
deleted
424.11
"…supply conductors with over 60°C insulation…"
"…supply conductors with an insulation rating greater than 60°C…"
reword
424.12(B)
"…shall be listed for such locations and shall be constructed and installed so that water or other liquids cannot enter or accumulate…"
"…shall be listed for such locations." (the water-accumulation sentence is dropped; both INs retained)
substantive
424.19 lead
"…shall be lockable in accordance with 110.25."
"…shall be capable of being locked in the open position in compliance with 110.25."
reword
424.19(B)(1)
"…or is lockable in accordance with 110.25."
"…or is capable of being locked in the open position in compliance with 110.25."
reword
424.19(C)(1)/(C)(2)
"…shall also be permitted to control lamps and appliances."
"…shall also be permitted to control general-purpose circuits and appliance circuits."
reword
424.20(A)
four conditions, ending "(4) Located as specified in 424.19."
NEW fifth condition: "(5) Located in an accessible location."
new requirement
424.22(A)
"…required by Articles 430 and 440… branch circuits in Article 210."
"…required to have additional overcurrent protection by Parts III and IV of Article 430 or Parts III and VI of Article 440… branch circuits in Part II of Article 210."
reword
424.22(B)
"…shall comply with 424.3(B)."
"…shall comply with 424.4(B)." (following the renumber; the 60 A / 48 A core unchanged)
cross-ref
424.28(B)
"…visible or easily accessible after installation."
"…visible or accessible after installation."
editorial
Unchanged (word-identical 2017→2023, machine-verified): 424.6 (listed equipment), 424.12(A) (physical damage), 424.13 (spacing from combustibles), 424.19(A) core (to "if fuses"), 424.19(C) lead (unit-switch permission), 424.19(C)(3) (one-family), 424.19(C)(4) (other occupancies), 424.20(B) (thermostats that do not directly interrupt), 424.21 (indicating type), 424.22(B) 60 A / 48 A element-subdivision core, 424.22(D) (branch-circuit conductors + 50 kW 100% escape), 424.22(E) (field-wired 125% + 50 kW 100% escape), 424.29 (heating-element marking) — thirteen identity checks, all passing. No ampere, watt, or percentage number in Parts I–IV moved between editions; every 2023 change is a renumber, a cross-reference update, a reword, the one new 424.20(A) condition, and the 424.10 deletion.
Worked examples (core-computed)
Every rating below is computed by the shipped PanelWright cores under node (compute_art60.js → art60_numbers.json) — nextStdBreaker (240.6 standard sizes), pickConductor31016 (Table 310.16), reqBreakerA (125% continuous). Zero hand math.
EX1 — the 424.4(B) 125% continuous-load conductor rule on a single large baseboard heater
A 12,000 W / 240 V baseboard heater on its own individual branch circuit. 424.4(A) permits an individual circuit to supply any rating for which it is rated; 424.4(B) (the 2023 reword) sizes the conductors at 125% of the load because it is a continuous load:
Step
Value
Rule
Heater load (12,000 W ÷ 240 V)
50 A
nameplate
Continuous-load conductor ampacity (125%)
62.5 A
424.4(B) — "ampacity shall not be less than 125 percent of the load"
OCPD (next standard at 62.5 A)
70 A
240.6 (nextStdBreaker)
Supply conductors (62.5 A @ 75 °C)
6 AWG Cu (65 A)
Table 310.16 (pickConductor31016)
The 125% is the whole of 424.4(B): a 50 A nameplate load needs 62.5 A of conductor ampacity, which lands a 6 AWG Cu (65 A) with a 70 A OCPD. In 2017 the same number came from the "considered continuous load" declaration + 210.20(A) 125%; in 2023 the 125% is written directly onto the conductors.
EX2 — the 424.4(A) 30 A multi-outlet cap (two baseboard heaters)
Two 2,400 W / 240 V baseboard heaters (4,800 W total = 20 A continuous) share one branch circuit — two outlets for fixed electric space-heating. 424.4(A) caps such a circuit at 30 A:
Step
Value
Rule
Combined load (4,800 W ÷ 240 V)
20 A
nameplate (two heaters)
Circuit rating cap
30 A
424.4(A) — "two or more outlets … rated not over 30 amperes"
Continuous-load conductor ampacity (125%)
25 A
424.4(B)
OCPD (next standard at 25 A, under the 30 A cap)
25 A
240.6 (nextStdBreaker); 25 A < 30 A cap
Conductor core pick (25 A @ 75 °C)
12 AWG Cu (25 A)
Table 310.16 — but see the 240.4(D) note
The 30 A cap does not bind here (the 125% value is 25 A, already under 30 A) — it is a ceiling, not a floor. The real trap is 240.4(D): a 12 AWG Cu conductor is capped at a 20 A OCPD, so a 12 AWG cannot legally feed a 25 A OCPD. The core picks 12 AWG by ampacity (25 A ≥ 25 A required), but to pair with the 25 A OCPD this 20 A continuous load actually requires, step the conductor up to 10 AWG Cu (30 A @ 75 °C). The 240.4(D) 20 A cap is flagged by the shipped core itself.
EX3 — the 424.22(B) 48 A element subdivision on a large heater
A 15,000 W / 240 V heater = 62.5 A nameplate — over the 48 A threshold. 424.22(B) requires the heating elements to be subdivided so each subdivided load is 48 A or less:
Step
Value
Rule
Nameplate load (15,000 W ÷ 240 V)
62.5 A
nameplate
48 A subdivision threshold
exceeded
424.22(B) — "equipment rated more than 48 amperes … shall have the heating elements subdivided"
Subdivisions (two equal elements)
2 × 31.25 A
each ≤ 48 A
Each subdivided load within 48 A
yes (31.25 A)
424.22(B) — "each subdivided load shall not exceed 48 amperes"
The 62.5 A heater cannot have a single 62.5 A resistance element (the 60 A element protection ceiling of 424.22(B) is also breached). Splitting it into two 7,500 W / 31.25 A elements satisfies both the 60 A element ceiling and the 48 A per-subdivision rule; the supplementary devices for those subdivisions follow 424.22(C) (factory-installed, accessible, suitable for branch-circuit protection) and their rating complies with 424.4(B) (2023; 2017 cited 424.3(B)).
EX4 — the 424.19(B)(1) breaker-as-disconnect on a motor-less heater
A 4,800 W / 240 V baseboard heater (20 A), no motor (or a motor not over 1/8 hp). 424.19(B)(1) lets the branch-circuit breaker BE the disconnecting means, in sight or lockable-open (110.25); the 424.19 lead rates the disconnect at 125% of the load:
Step
Value
Rule
Heater load (4,800 W ÷ 240 V)
20 A
nameplate
Disconnect rating floor (125% of load)
25 A
424.19 lead — "not less than 125 percent of the total load of the motors and the heaters"
Disconnect OCPD (next standard at 25 A)
25 A
240.6 (nextStdBreaker)
Location condition
in sight OR lockable-open
424.19(B)(1) + 110.25 (2023: "capable of being locked in the open position in compliance with 110.25")
The 25 A breaker is both the branch OCPD and the disconnecting means — no separate heater switch is required — provided it is within sight of the heater or lockable-open. The 2017 wording for that lock condition ("is lockable in accordance with 110.25") is exactly what 2023 rewords to the "locked in the open position in compliance with 110.25" form.
EX5 — the 424.4(A) non-dwelling 50 A infrared allowance
A 4,800 W / 120 V infrared heater (40 A continuous) in a commercial (non-dwelling) space, on its own circuit. 424.4(A) permits non-dwelling fixed infrared heating equipment on branch circuits rated not over 50 A:
Step
Value
Rule
Infrared heater load (4,800 W ÷ 120 V)
40 A
nameplate
Non-dwelling infrared circuit cap
50 A
424.4(A) — "in other than a dwelling unit, fixed infrared … not over 50 amperes"
Continuous-load conductor ampacity (125%)
50 A
424.4(B)
OCPD (next standard at 50 A)
50 A
240.6 (nextStdBreaker); 50 A = the cap
Supply conductors (50 A @ 75 °C)
8 AWG Cu (50 A)
Table 310.16 (pickConductor31016)
The 40 A infrared load rides right up to the 50 A non-dwelling infrared allowance: 125% = 50 A, which is exactly the 424.4(A) ceiling, so an 8 AWG Cu (50 A) with a 50 A OCPD is the package. (In a dwelling the 30 A multi-outlet cap of 424.4(A) would have applied to a multi-outlet infrared circuit instead — the 50 A route is the non-dwelling infrared exception.)
Where 424.1–424.29 fit
The appliance-side neighbor: the NEC 422.10–422.13 appliance branch-circuit article (56) — 422.10/422.11 size the appliance circuit and OCPD and 422.13 makes the water heater a 125% continuous load; Article 424 is the fixed space-heating cousin (baseboard, duct, boiler, radiant) where the 125% continuous rule lives in 424.4(B) instead of 422.13.
The multi-motor hand-off: the NEC 430.24 + 430.53 several-motors article (57) — 430.24's conductor sum explicitly routes the space-heating load to 424.4(B) (the 125% continuous-load conductor rule this article documents); the 2017 424.3(B) cross-reference that 430.24 used is the one 2023 renumbers to 424.4(B).
The appliance disconnecting-means neighbor: the NEC 422.30–422.62 appliance disconnecting-means article (59) — 424.19(A)(2)(2) routes a motor-driven heater with a compliant unit switch to 422.34(A), (B), (C), or (D) (the out-of-sight allowance), the same unit-switch rules Article 424 leans on.
The air-conditioning / refrigerating cross-reference: the NEC 440.22 + 440.32 air-conditioning branch-circuit article (50) — 424.2 (2017) / 424.3 + Table 424.3 (2023) sends a compressor-equipped space heater to Article 440 (Parts I–VI), which is the source of the 175% / 125% / 72% rules that article works.
Scope boundary, stated: this article is exactly 424.1–424.29 — Part I General (424.1–424.6), Part II Installation (424.9–424.13), Part III Control and Protection (424.19–424.22), and Part IV Marking (424.28–424.29). The rest of Article 424 is adjacent scope outside this article: Part V Electric Space-Heating Cables (424.34–424.48), Part VI Duct Heaters (424.57–424.66), Part VII Resistance-Type Boilers (424.70–424.74), Part VIII Electrode-Type Boilers (424.80–424.86), Part IX Radiant Heating Panels (424.90–424.99), and Part X Low-Voltage (424.100–424.104) — the on-disk 2017 scan carries all of it (verified) and the 2023 CSV carries the remaining 106 rows (138 total 424.x rows, 32 in this article's scope). 2020 position is not asserted: no on-disk 2020 source carries the 424.1–424.29 section bodies (the on-disk 2020 scan ends at Article 230; verified), so the edition story is 2017↔2023 only. Verify section numbers against the NEC edition adopted in your jurisdiction.
Method, sources & honesty notes
Section text. Verbatim NEC 2017 (official NFPA text on disk, nec2017_full.txt, lines 49567–50943 reflowed to art60_2017_cont.txt with scan furniture stripped — page numbers 70-281…70-287, the edition lines, the ARTICLE 424 banner, and the running-header bare section numbers 424.19/424.20/424.43/424.82/424.83/424.101/424.102): 424.1, 424.2, 424.3 (A)/(B), 424.6, 424.9, 424.10, 424.11, 424.12 (A)/(B), 424.13, 424.19 lead/(A)/(A)(1)/(A)(2)/(B)(1)/(B)(2)/(C)/(C)(1)–(C)(4), 424.20 (A)/(B), 424.21, 424.22 (A)–(E), 424.28 (A)/(B), 424.29. OCR line-wrap reflow normalized; disclosed scan artifacts corrected (listed per quote block): the 1/8-hp fraction printing as "% hp" (424.19(A)(1)/(A)(2)/(B)(1)/(B)(2), 424.28(A)), the comma-for-period "424,99(B)" / "424,22(C)" in 424.22(C) (resolves to 424.22(B); the clean 2023 row confirms it), and the page-break running header "424.19" printed mid-424.19(A) (removed). No other wording altered.
2023 text. On-disk 2023 NEC CSV (art35_nec_csv.csv): 32 in-scope rows — 424.1; 424.3; 424.4(A)/(B); 424.6; 424.10; 424.11; 424.12(A)/(B); 424.13; 424.19 lead/(A)/(A)(1)/(A)(2)/(B)(1)/(B)(2)/(C)/(C)(1)/(C)(2)/(C)(3)/(C)(4); 424.20(A)/(B); 424.21; 424.22(A)–(E); 424.28(A)/(B); 424.29 — complete for the scope (verified: the row set matches exactly; no 424.9 row, and no 424.10 "Special Permission" row — confirming the 424.9→424.10 renumber and the 424.10 deletion). The CSV carries 138 424.x rows total; the other 106 are the cable/duct/boiler/radiant/low-voltage parts out of this article's scope.
Worked examples (core-computed). Every rating is computed by the shipped PanelWright cores under node (compute_art60.js → art60_numbers.json): nextStdBreaker (240.6 standard sizes), pickConductor31016 (Table 310.16 pick + the 240.4(D) small-conductor OCPD caps), reqBreakerA (125% continuous). Zero hand math — the EX1/EX2/EX4/EX5 loads are nameplate watts ÷ volts, the 125% and next-standard steps are core calls, and the conductor picks are core calls.
Edition-delta claims (machine-checked). A targeted assertion script (verify_art60.py) reads the on-disk 2017 NFPA scan (reflowed), the on-disk 2023 NEC CSV, and the on-disk Mike Holt 2023 change summary and asserts 72 phrase-level checks: 25 verbatim-2017 presence probes (every in-scope section's 2017 text, each delta's 2017 side), 13 verbatim-2023 presence probes (each delta's 2023 side, including the 424.4(B) 125% conductor reword, the 424.11 "insulation rating greater than 60°C" reword, the 424.20(A) "Located in an accessible location" new condition, and the 424.22(A)/(B) rewords), 10 one-sided delta-absence probes from the 2023 side (the "shall be considered continuous load" drop, the 424.10 special-permission deletion, the 424.11 "over 60°C insulation" drop, the 424.12(B) water-sentence drop, the 424.19 "lockable in accordance with 110.25" drop, the 424.19(C) "control lamps and appliances" drop, the 424.22(A) old cross-ref drop, the 424.22(B) 424.3(B) drop, the 424.28(B) "easily accessible" drop, and the 210.50(B) drop), 3 one-sided NEW-in-2023 probes from the 2017 side (the 424.20(A) accessible-location condition, the Table 424.3, and the 424.4(B) 125% conductor sentence are all absent from the 2017 scan), 5 renumber/deletion proofs (424.4(B) row present; no 424.3 branch-circuits row; no 424.9 row; no 424.10 special-permission row; 424.10 carries the 210.52 baseboard text), 13 word-identity checks (alpha-normalized 2017↔2023: 424.6, 424.12(A), 424.13, 424.19(A) core, 424.19(C) lead, 424.19(C)(3), 424.19(C)(4), 424.20(B), 424.21, 424.22(B) elements, 424.22(D), 424.22(E), 424.29), 2 Mike Holt probes (the 424.4 (B) reword entry present; exactly ONE in-scope Article-424 entry in the whole summary — 424.4 — so every other delta is on-disk-verified with ELR silence), and the 32-row CSV completeness check (25 + 13 + 10 + 3 + 5 + 13 + 2 + 1 = 72). All 72 pass (re-runnable, exit 0). 2020 position is not asserted: no on-disk 2020 source carries the 424.1–424.29 section bodies (verified against the on-disk 2020 scan, which ends at Article 230).