NEC 245 — Overcurrent Protection for Systems Over 1000 V (Medium Voltage)
The article that answers "my feeder is 13.8 kV — where are the overcurrent-protection rules, and what did the 2023 NEC do with the old 240.100/240.101 and 490.21?" In 2017 the medium-voltage overcurrent rules lived in two places: Article 240 Part IX (240.100 Feeders and Branch Circuits + 240.101 Additional Requirements for Feeders) and Article 490 Part II (490.21 Circuit-Interrupting Devices — the section that left Article 490 in 2023, documented in article 63). In 2023 they were consolidated into one brand-new article: Article 245, "Overcurrent Protection for Systems Rated Over 1000V ac, 1500V dc" — with 240.100 → 245.26 (protection in each ungrounded conductor; the 3-CT / 3-relay-element rule; the 250.184(B) neutral-reground CT-link condition), 240.101 → 245.27 (the 3×/6× OCPD rating/setting caps + the feeder-tap rule), 490.21 → 245.21 (circuit breakers / power fuses & fuseholders / distribution cutouts / oil-filled cutouts / load-interrupter switches), and two genuinely NEW sections: 245.1 Scope and 245.2 Reconditioned Equipment (permitted: MV/HV breakers, electromechanical relays, CTs; barred: MV fuseholders + nonrenewable fuses). All 44 on-disk 2023 rows quoted below, the verbatim 2017 source sections quoted, 5 machine-diffed text deltas in 245.21 (the "maximum → available fault current" interrupting-rating tightening in four places + the 245.21(E) warning-sign rewrite), one flagged on-disk data artifact (the 245.26(A) method reference), and three core-computed worked examples — 179 machine-verified checks.
What this is. A free, design-aid explainer of the NEC's 2023 medium-voltage overcurrent-protection article (Article 245) and the 2017 → 2023 consolidation behind it, for electricians, engineers, and the inspectors who check it. 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 2017 section text is quoted from the verbatim 2017 NEC (official NFPA scan on disk) with disclosed OCR fixes; the 2023 side is quoted/verified against the on-disk 2023 NEC dataset (the anthonymeo/NEC-csv export — all 44 Article 245 rows are on disk, so this is a real word-level 2017→2023 diff, not a change-summary record). Honesty notes, stated up front: (1) the Mike Holt on-disk 2023 change summary lists Article 245 only as one of the new medium-voltage articles (no section-level 245 entries) — every section-level delta on this page is therefore a direct machine diff of the on-disk 2017 scan vs the on-disk 2023 dataset, and where a change could first have landed in 2020 the page says so rather than claiming 2023 origin; (2) the on-disk 245.26(A) row prints its method self-reference as "either 250.184(B) or (A)(2)" — flagged as a data artifact of the export (the 2017 text is "either 240.100(A)(1) or (A)(2)"), NOT asserted as adopted code text; (3) the 2017 scan carries a few OCR artifacts in the 490.21 region (listed in Method) — they are disclosed, not silently repaired.
Why this article exists — the 2017 split and the 2023 consolidation
In the 2017 NEC, overcurrent protection for systems over 1000 volts nominal was split across two articles:
Article 240, Part IX "Overcurrent Protection over 1000 Volts, Nominal" — exactly two sections: 240.100 (feeder/branch-circuit OCPD: location and type, the 3-phase CT/relay rule, protective-device and conductor-protection requirements) and 240.101 (additional feeder requirements: the 3×/6× OCPD rating/setting caps and the feeder-tap rule). Machine-verified: the Part IX region of the on-disk 2017 scan contains only the 240.100 and 240.101 headings — no other 240.1xx sections.
Article 490, Part II "Equipment — Specific Provisions" — 490.21 Circuit-Interrupting Devices (circuit breakers, power fuses and fuseholders, distribution cutouts and expulsion fuse links, oil-filled cutouts, load-interrupter switches), sitting beside 490.22–490.25 (isolation, regulators, clearances, backfeed).
In the 2023 NEC, all three sections moved into the new Article 245, and the two source articles shed them: the on-disk 2023 dataset has no 240.100/240.101 rows (Article 240 Part IX is gone), and Article 490 became Article 495 with no 495.21 row (documented in article 63). Mike Holt's on-disk 2023 change summary confirms the new article in its "New Medium Voltage Articles" list (235 / 245 / 305 / 315 / 495). The consolidation map, machine-counted:
2017 location
2023 landing
Word coverage (machine)
Content
240.100 Feeders and Branch Circuits (Art 240 Part IX)
NEW 245.1 Scope (1 row) — "This article covers overcurrent protection requirements for systems over 1000 volts ac, 1500 volts dc, nominal."
—
2017 had no standalone scope section for this content
NEW 245.2 Reconditioned Equipment (2 rows: (A), (B))
—
(A) permits reconditioned MV/HV breakers, electromechanical protective relays, CTs; (B) bars reconditioned MV fuseholders + nonrenewable fuses — "reconditioned" absent from both 2017 source regions (machine-asserted)
Total on-disk 2023 rows: 44 across exactly five section families (245.1 / 245.2 / 245.21 / 245.26 / 245.27) — there are no 245.3–245.25 or 245.28+ rows in the dataset (machine-verified).
The 2017 source sections, verbatim
Quoted from the on-disk 2017 NEC scan (disclosed OCR fixes in Method). Each block's footer carries its 2023 landing.
Article 240, Part IX — Overcurrent Protection over 1000 Volts, Nominal
240.100 Feeders and Branch Circuits.2017 verbatim (on-disk scan). 2023: → 245.26 — relocated to the new Article 245; the only textual moves are the section number and the (A) method self-reference (the on-disk 2023 row prints "either 250.184(B) or (A)(2)" — flagged data artifact, see honesty notes). (A)(1), (A)(2), (B), (C) word-identical.
Part IX. Overcurrent Protection over 1000 Volts, Nominal
240.100 Feeders and Branch Circuits.
(A) Location and Type of Protection. Feeder and branchcircuit conductors shall have overcurrent protection in each ungrounded conductor located at the point where the conductor receives its supply or at an alternative location in the circuit when designed under engineering supervision that includes but is not limited to considering the appropriate fault studies and time-current coordination analysis of the protective devices and the conductor damage curves. The overcurrent protection shall be permitted to be provided by either 240.100(A) (1) or (A) (2).
(1) Overcurrent Relays and Current Transformers. Circuit breakers used for overcurrent protection of 3-phase circuits shall have a minimum of three overcurrent relay elements operated from three current transformers. The separate overcurrent relay elements (or protective functions) shall be permitted to be part of a single electronic protective relay unit. On 3-phase, 3-wire circuits, an overcurrent relay element in the residual circuit of the current transformers shall be permitted to replace one of the phase relay elements. An overcurrent relay element, operated from a current transformer that links all phases of a 3-phase, 3-wire circuit, shall be permitted to replace the residual relay element and one of the phase-conductor current transformers. Where the neutral conductor is not regrounded on the load side of the circuit as permitted in 250.184(B), the current transformer shall be permitted to link all 3-phase conductors and the grounded circuit conductor (neutral).
(2) Fuses. A fuse shall be connected in series with each ungrounded conductor.
(B) Protective Devices. The protective device(s) shall be capable of detecting and interrupting all values of current that can occur at their location in excess of their trip-setting or melting point.
(C) Conductor Protection. The operating time of the protective device, the available short-circuit current, and the conductor used shall be coordinated to prevent damaging or dangerous temperatures in conductors or conductor insulation under short-circuit conditions.
240.101 Additional Requirements for Feeders.2017 verbatim (on-disk scan). 2023: → 245.27 — relocated to the new Article 245. The 3×/6× caps and the feeder-tap rule are word-identical; only the 695.4(B) (2) → 695.4(B)(2) scan-spacing fix moved.
240.101 Additional Requirements for Feeders.
(A) Rating or Setting of Overcurrent Protective Devices. The continuous ampere rating of a fuse shall not exceed three times the ampacity of the conductors. The long-time trip element setting of a breaker or the minimum trip setting of an electronically actuated fuse shall not exceed six times the ampacity of the conductor. For fire pumps, conductors shall be permitted to be protected for overcurrent in accordance with 695.4(B) (2).
(B) Feeder Taps. Conductors tapped to a feeder shall be permitted to be protected by the feeder overcurrent device where that overcurrent device also protects the tap conductor.
Article 490, Part II — 490.21 Circuit-Interrupting Devices
490.21 (A) Circuit Breakers.2017 verbatim (on-disk scan; OCR fixes disclosed in Method: the "(MVA)}" stray-brace artifact). 2023: → 245.21(A) (5 rows) — (1)–(3) word-identical; the (4) interrupting-rating floor "maximum fault current" → "available fault current" (delta 1 of 5); NEW (5) retrofit-trip-unit listing requirement (no 2017 counterpart line).
(A) Circuit Breakers.
(1) Location. (a) Circuit breakers installed indoors shall be mounted either in metal-enclosed units or fire-resistant cell-mounted units, or they shall be permitted to be open-mounted in locations accessible to qualified persons only. (b) Circuit breakers used to control oil-filled transformers in a vault shall either be located outside the transformer vault or be capable of operation from outside the vault. (c) Oil circuit breakers shall be arranged or located so that adjacent readily combustible structures or materials are safeguarded in an approved manner.
(2) Operating Characteristics. Circuit breakers shall have the following equipment or operating characteristics: (1) An accessible mechanical or other identified means for manual tripping, independent of control power (2) Be release free (trip free) (3) If capable of being opened or closed manually while energized, main contacts that operate independently of the speed of the manual operation (4) A mechanical position indicator at the circuit breaker to show the open or closed position of the main contacts (5) A means of indicating the open and closed position of the breaker at the point(s) from which they may be operated
(3) Nameplate. A circuit breaker shall have a permanent and legible nameplate showing manufacturer's name or trademark, manufacturer's type or identification number, continuous current rating, interrupting rating in megavolt-amperes (MVA)} or amperes, and maximum voltage rating. Modification of a circuit breaker affecting its rating(s) shall be accompanied by an appropriate change of nameplate information.
(4) Rating. Circuit breakers shall have the following ratings: (1) The continuous current rating of a circuit breaker shall not be less than the maximum continuous current through the circuit breaker. (2) The interrupting rating of a circuit breaker shall not be less than the maximum fault current the circuit breaker will be required to interrupt, including contributions from all connected sources of energy. (3) The closing rating of a circuit breaker shall not be less than the maximum asymmetrical fault current into which the circuit breaker can be closed. (4) The momentary rating of a circuit breaker shall not be less than the maximum asymmetrical fault current at the point of installation. (5) The rated maximum voltage of a circuit breaker shall not be less than the maximum circuit voltage.
490.21 (B) Power Fuses and Fuseholders.2017 verbatim (on-disk scan; the page-bleed "490.21" artifact inside (1) Use is the scan's running page marker, as quoted in article 63; "gangoperated" in (7) is a 2017 scan artifact — the 2023 hyphenated "gang-operated" is not a code delta). 2023: → 245.21(B) (7 rows) — (1)/(3)–(7) word-identical; (2) "maximum fault current" → "available fault current" (delta 2 of 5).
(B) Power Fuses and Fuseholders.
(1) Use. Where fuses are used to protect conductors and equipment, a fuse shall be placed in each ungrounded conductor. Two power fuses shall be permitted to be used in parallel to protect the same load if both fuses have identical ratings and both fuses are installed in an identified common mounting with electrical connections that divide the current equally. Power fuses of the vented type shall not be used indoors, 490.21 underground, or in metal enclosures unless identified for the use,
(2) Interrupting Rating. The interrupting rating of power fuses shall not be less than the maximum fault current the fuse is required to interrupt, including contributions from all connected sources of energy.
(3) Voltage Rating. The maximum voltage rating of power fuses shall not be less than the maximum circuit voltage. Fuses having a minimum recommended operating voltage shall not be applied below this voltage.
(4) Identification of Fuse Mountings and Fuse Units. Fuse mountings and fuse units shall have permanent and legible nameplates showing the manufacturer's type or designation, continuous current rating, interrupting current rating, and maximum voltage rating.
(5) Fuses. Fuses that expel flame in opening the circuit shall be designed or arranged so that they function properly without hazard to persons or property.
(6) Fuseholders. Fuseholders shall be designed or installed so that they are de-energized while a fuse is being replaced. A field-applied permanent and legible sign, in accordance with 110.21(B), shall be installed immediately adjacent to the fuseholders and shall be worded as follows: DANGER — DISCONNECT CIRCUIT BEFORE REPLACING FUSES. Exception: Fuses and fuseholders designed to permit fuse replacement by qualified persons using identified equipment without de-energizing the fuseholder shall be permitted.
(7) High-Voltage Fuses. Switchgear and substations that utilize high-voltage fuses shall be provided with a gangoperated disconnecting switch. Isolation of the fuses from the circuit shall be provided by either connecting a switch between the source and the fuses or providing roll-out switch and fusetype construction. The switch shall be of the load-interrupter type, unless mechanically or electrically interlocked with a loadinterrupting device arranged to reduce the load to the interrupting capability of the switch. Exception: More than one switch shall be permitted as the disconnecting means for one set of fuses where the switches are installed to provide connection to more than one set of supply conductors. The switches shail be mechanically or electrically interlocked to permit access to the fuses only when all switches are open. A conspicuous sign shall be placed at the fuses identifying the presence of more than one source.
490.21 (C) Distribution Cutouts and Fuse Links — Expulsion Type.2017 verbatim (on-disk scan). 2023: → 245.21(C) (7 rows) — (1)/(2)/(4)–(7) word-identical; (3) "maximum fault current" → "available fault current" (delta 3 of 5).
(C) Distribution Cutouts and Fuse Links — Expulsion Type.
(1) Installation. Cutouts shall be located so that they may be readily and safely operated and re-fused, and so that the exhaust of the fuses does not endanger persons. Distribution cutouts shall not be used indoors, underground, or in metal enclosures.
(2) Operation. Where fused cutouts are not suitable to interrupt the circuit manually while carrying full load, an approved means shall be installed to interrupt the entire load. Unless the fused cutouts are interlocked with the switch to prevent opening of the cutouts under load, a conspicuous sign shall be placed at such cutouts identifying that they shall not be operated under load.
(3) Interrupting Rating. The interrupting rating of distribution cutouts shall not be less than the maximum fault current the cutout is required to interrupt, including contributions from all connected sources of energy.
(4) Voltage Rating. The maximum voltage rating of cutouts shall not be less than the maximum circuit voltage.
(5) Identification. Distribution cutouts shall have on their body, door, or fuse tube a permanent and legible nameplate or identification showing the manufacturer's type or designation, continuous current rating, maximum voltage rating, and interrupting rating.
(6) Fuse Links. Fuse links shall have a permanent and legible identification showing continuous current rating and type.
(7) Structure Mounted Outdoors. The height of cutouts mounted outdoors on structures shall provide safe clearance between lowest energized parts (open or closed position) and standing surfaces, in accordance with 110.34(E).
490.21 (D) Oil-Filled Cutouts.2017 verbatim (on-disk scan; "shail" in (3) is a 2017 scan OCR error for "shall" — a 2017-side fix, not a code delta). 2023: → 245.21(D) (8 rows) — (1)/(3)–(8) word-identical; (2) "maximum fault current" → "available fault current" (delta 4 of 5).
(D) Oil-Filled Cutouts.
(1) Continuous Current Rating. The continuous current rating of oil-filled cutouts shall not be less than the maximum continuous current through the cutout.
(2) Interrupting Rating. The interrupting rating of oil-filled cutouts shall not be less than the maximum fault current the oil-filled cutout is required to interrupt, including contributions from all connected sources of energy.
(3) Voltage Rating. The maximum voltage rating of oil-filled cutouts shail not be less than the maximum circuit voltage.
(4) Fault Closing Rating. Oil-filled cutouts shall have a fault closing rating not less than the maximum asymmetrical fault current that can occur at the cutout location, unless suitable interlocks or operating procedures preclude the possibility of closing into a fault.
(5) Identification. Oil-filled cutouts shall have a permanent and legible nameplate showing the rated continuous current, rated maximum voltage, and rated interrupting current.
(6) Fuse Links. Fuse links shall have a permanent and legible identification showing the rated continuous current.
(7) Location. Cutouts shall be located so that they are readily and. safely accessible for re-fusing, with the top of the cutout not over 1.5 m (5 ft) above the floor or platform.
(8) Enclosure. Suitable barriers or enclosures shall be provided to prevent contact with nonshielded cables or energized parts of oil-filled cutouts.
490.21 (E) Load Interrupters.2017 verbatim (on-disk scan; the "490.35" page-bleed mid-paragraph is the scan's running page marker, as quoted in article 63). 2023: → 245.21(E) (7 rows) — (1)–(6) word-identical; the lead paragraph carries delta 5 of 5: "interrupt fault currents" → "interrupt available fault currents" + the multi-source marking rewrite ("conspicuous sign identifying this hazard" → "warning sign identifying the presence of more than one source" + the 110.21 compliance sentence).
(E) Load Interrupters. Load-interrupter switches shall be permitted if suitable fuses or circuit breakers are used in conjunction with these devices to interrupt fault currents. Where these devices are used in combination, they shall be coordinated electrically so that they will safely withstand the effects of closing, carrying, or interrupting all possible currents up to the assigned maximum short-circuit rating. Where more than one switch is installed with interconnected load terminals to provide for alternate connection to different supply conductors, each switch shall be provided with a conspicuous sign identifying this hazard. 490.35
(1) Continuous Current Rating. The continuous current rating of interrupter switches shall equal or exceed the maximum continuous current at the point of installation.
(2) Voltage Rating. The maximum voltage rating of interrupter switches shall equal or exceed the maximum circuit voltage.
(3) Identification. Interrupter switches shall have a permanent and legible nameplate including the following information: manufacturer's type or designation, continuous current rating, interrupting current rating, fault closing rating, maximum voltage rating.
(4) Switching of Conductors. The switching mechanism shall be arranged to be operated from a location where the operator is not exposed to energized parts and shall be arranged to open all ungrounded conductors of the circuit simultaneously with one operation. Switches shall be arranged to be locked in the open position. Metal-enclosed switches shall be operable from outside the enclosure.
(5) Stored Energy for Opening. The stored-energy operator shall be permitted to be left in the uncharged position after the switch has been closed if a single movement of the operating handle charges the operator and opens the switch.
(6) Supply Terminals. The supply terminals of fused interrupter switches shall be installed at the top of the switch enclosure, or, if the terminals are located elsewhere, the equipment shall have barriers installed so as to prevent persons from accidentally contacting energized parts or dropping tools or fuses into energized parts.
The 2023 article, verbatim (all 44 on-disk rows)
Quoted from the on-disk 2023 NEC dataset (anthonymeo/NEC-csv export, rows → 2023.antflix.net). Every one of the 44 rows is quoted below — no 245.x row is left unquoted.
245.1 Scope — NEW (no 2017 counterpart)
245.1 Scope.2023 verbatim (on-disk dataset). NEW in 2023 — 2017's over-1000 V OCPD rules had no standalone scope section. Article title per the on-disk Mike Holt 2023 change summary: "Overcurrent Protection for Systems Rated Over 1000V ac, 1500V dc".
This article covers overcurrent protection requirements for systems over 1000 volts ac, 1500 volts dc, nominal.
245.2 Reconditioned Equipment — NEW (no 2017 counterpart)
245.2 Reconditioned Equipment.2023 verbatim (on-disk dataset; the (A) list items run together in the export — two items: "Medium- and high-voltage circuit breakers" / "Electromechanical protective relays and current transformers" — reflow artifact, not a fix). NEW in 2023 — "reconditioned" is absent from the 2017 240 Part IX region and the 2017 490.21 region (machine-asserted). Companion: new 110.20 Reconditioned Equipment (general requirements, outside this article's on-disk scope).
The following reconditioned equipment shall be permitted: Medium- and high-voltage circuit breakersElectromechanical protective relays and current transformers
Medium-voltage fuseholders and medium-voltage nonrenewable fuses shall not be permitted.
245.26 Feeders and Branch Circuits (= 2017 240.100)
245.26 Feeders and Branch Circuits.2023 verbatim (on-disk dataset, 5 rows). = 2017 240.100, word-identical in (A)(1)/(A)(2)/(B)/(C); the (A) method self-reference is the flagged data artifact ("either 250.184(B) or (A)(2)" on disk vs 2017 "either 240.100(A)(1) or (A)(2)").
[245.26(A)] Feeder and branch-circuit conductors shall have overcurrent protection in each ungrounded conductor located at the point where the conductor receives its supply or at an alternative location in the circuit when designed under engineering supervision that includes but is not limited to considering the appropriate fault studies and time-current coordination analysis of the protective devices and the conductor damage curves. The overcurrent protection shall be permitted to be provided by either 250.184(B) or (A)(2).
[245.26(A)(1)] Circuit breakers used for overcurrent protection of 3-phase circuits shall have a minimum of three overcurrent relay elements operated from three current transformers. The separate overcurrent relay elements (or protective functions) shall be permitted to be part of a single electronic protective relay unit. On 3-phase, 3-wire circuits, an overcurrent relay element in the residual circuit of the current transformers shall be permitted to replace one of the phase relay elements. An overcurrent relay element, operated from a current transformer that links all phases of a 3-phase, 3-wire circuit, shall be permitted to replace the residual relay element and one of the phase-conductor current transformers. Where the neutral conductor is not regrounded on the load side of the circuit as permitted in 250.184(B), the current transformer shall be permitted to link all 3-phase conductors and the grounded circuit conductor (neutral).
[245.26(A)(2)] A fuse shall be connected in series with each ungrounded conductor.
[245.26(B)] The protective device(s) shall be capable of detecting and interrupting all values of current that can occur at their location in excess of their trip-setting or melting point.
[245.26(C)] The operating time of the protective device, the available short-circuit current, and the conductor used shall be coordinated to prevent damaging or dangerous temperatures in conductors or conductor insulation under short-circuit conditions.
245.27 Additional Requirements for Feeders (= 2017 240.101)
245.27 Additional Requirements for Feeders.2023 verbatim (on-disk dataset, 2 rows). = 2017 240.101, word-identical (only the 695.4(B) (2) → 695.4(B)(2) scan-spacing fix). The 3×/6× OCPD caps — unchanged since at least 2017.
[245.27(A)] The continuous ampere rating of a fuse shall not exceed three times the ampacity of the conductors. The long-time trip element setting of a breaker or the minimum trip setting of an electronically actuated fuse shall not exceed six times the ampacity of the conductor. For fire pumps, conductors shall be permitted to be protected for overcurrent in accordance with 695.4(B)(2).
[245.27(B)] Conductors tapped to a feeder shall be permitted to be protected by the feeder overcurrent device where that overcurrent device also protects the tap conductor.
245.21 (A) Circuit Breakers.2023 verbatim (on-disk dataset, 5 rows). = 2017 490.21(A): (1)–(3) word-identical; (4) "maximum" → "available fault current" (delta 1); NEW (5) retrofit trip units "shall be listed for use with the specific circuit breaker" — no 2017 counterpart line (first appearance in the on-disk text).
Circuit breakers installed indoors shall be mounted either in metal-enclosed units or fire-resistant cell-mounted units, or they shall be permitted to be open-mounted in locations accessible to qualified persons only.Circuit breakers used to control oil-filled transformers in a vault shall either be located outside the transformer vault or be capable of operation from outside the vault.Oil circuit breakers shall be arranged or located so that adjacent readily combustible structures or materials are safeguarded in an approved manner.
Circuit breakers shall have the following equipment or operating characteristics: An accessible mechanical or other identified means for manual tripping, independent of control powerBe release free (trip free)If capable of being opened or closed manually while energized, main contacts that operate independently of the speed of the manual operationA mechanical position indicator at the circuit breaker to show the open or closed position of the main contactsA means of indicating the open and closed position of the breaker at the point(s) from which they may be operated
A circuit breaker shall have a permanent and legible nameplate showing the manufacturer's name or trademark, manufacturer's type or identification number, continuous current rating, interrupting rating in megavolt-amperes (MVA) or amperes, and maximum voltage rating. Modification of a circuit breaker affecting its rating(s) shall be accompanied by an appropriate change of nameplate information.
Circuit breakers shall have the following ratings: The continuous current rating of a circuit breaker shall not be less than the maximum continuous current through the circuit breaker.The interrupting rating of a circuit breaker shall not be less than the available fault current the circuit breaker will be required to interrupt, including contributions from all connected sources of energy.The closing rating of a circuit breaker shall not be less than the maximum asymmetrical fault current into which the circuit breaker can be closed.The momentary rating of a circuit breaker shall not be less than the maximum asymmetrical fault current at the point of installation.The rated maximum voltage of a circuit breaker shall not be less than the maximum circuit voltage.
Retrofit trip units shall be listed for use with the specific circuit breaker with which it is installed.
245.21 (B) Power Fuses and Fuseholders.2023 verbatim (on-disk dataset, 7 rows). = 2017 490.21(B): (1)/(3)–(7) word-identical (incl. the "DANGER – DISCONNECT CIRCUIT BEFORE REPLACING FUSES" sign wording in (6)); (2) "maximum" → "available fault current" (delta 2).
Where fuses are used to protect conductors and equipment, a fuse shall be placed in each ungrounded conductor. Two power fuses shall be permitted to be used in parallel to protect the same load if both fuses have identical ratings and both fuses are installed in an identified common mounting with electrical connections that divide the current equally. Power fuses of the vented type shall not be used indoors, underground, or in metal enclosures unless identified for the use.
The interrupting rating of power fuses shall not be less than the available fault current the fuse is required to interrupt, including contributions from all connected sources of energy.
The maximum voltage rating of power fuses shall not be less than the maximum circuit voltage. Fuses having a minimum recommended operating voltage shall not be applied below this voltage.
Fuse mountings and fuse units shall have permanent and legible nameplates showing the manufacturer's type or designation, continuous current rating, interrupting current rating, and maximum voltage rating.
Fuses that expel flame in opening the circuit shall be designed or arranged so that they function properly without hazard to persons or property.
Fuseholders shall be designed or installed so that they are de-energized while a fuse is being replaced. A field-applied permanent and legible sign, in accordance with 110.21(B), shall be installed immediately adjacent to the fuseholders and shall be worded as follows: DANGER - DISCONNECT CIRCUIT BEFORE REPLACING FUSES. Exception: Fuses and fuseholders designed to permit fuse replacement by qualified persons using identified equipment without de-energizing the fuseholder shall be permitted.
Switchgear and substations that use high-voltage fuses shall be provided with a gang-operated disconnecting switch. Isolation of the fuses from the circuit shall be provided by either connecting a switch between the source and the fuses or providing roll-out switch and fuse-type construction. The switch shall be of the load-interrupter type, unless mechanically or electrically interlocked with a load-interrupting device arranged to reduce the load to the interrupting capability of the switch. Exception: More than one switch shall be permitted as the disconnecting means for one set of fuses where the switches are installed to provide connection to more than one set of supply conductors. The switches shall be mechanically or electrically interlocked to permit access to the fuses only when all switches are open. A conspicuous sign shall be placed at the fuses identifying the presence of more than one source.
245.21 (C) Distribution Cutouts.2023 verbatim (on-disk dataset, 7 rows). = 2017 490.21(C): (1)/(2)/(4)–(7) word-identical; (3) "maximum" → "available fault current" (delta 3).
Cutouts shall be located so that they may be readily and safely operated and re-fused, and so that the exhaust of the fuses does not endanger persons. Distribution cutouts shall not be used indoors, underground, or in metal enclosures.
Where fused cutouts are not suitable to interrupt the circuit manually while carrying full load, an approved means shall be installed to interrupt the entire load. Unless the fused cutouts are interlocked with the switch to prevent opening of the cutouts under load, a conspicuous sign shall be placed at such cutouts identifying that they shall not be operated under load.
The interrupting rating of distribution cutouts shall not be less than the available fault current the cutout is required to interrupt, including contributions from all connected sources of energy.
The maximum voltage rating of cutouts shall not be less than the maximum circuit voltage.
Distribution cutouts shall have on their body, door, or fuse tube a permanent and legible nameplate or identification showing the manufacturer's type or designation, continuous current rating, maximum voltage rating, and interrupting rating.
Fuse links shall have a permanent and legible identification showing continuous current rating and type.
The height of cutouts mounted outdoors on structures shall provide safe clearance between lowest energized parts (open or closed position) and standing surfaces, in accordance with 110.34(E).
245.21 (D) Oil-Filled Cutouts.2023 verbatim (on-disk dataset, 8 rows). = 2017 490.21(D): (1)/(3)–(8) word-identical; (2) "maximum" → "available fault current" (delta 4).
The continuous current rating of oil-filled cutouts shall not be less than the maximum continuous current through the cutout.
The interrupting rating of oil-filled cutouts shall not be less than the available fault current the oil-filled cutout is required to interrupt, including contributions from all connected sources of energy.
The maximum voltage rating of oil-filled cutouts shall not be less than the maximum circuit voltage.
Oil-filled cutouts shall have a fault closing rating not less than the maximum asymmetrical fault current that can occur at the cutout location, unless suitable interlocks or operating procedures preclude the possibility of closing into a fault.
Oil-filled cutouts shall have a permanent and legible nameplate showing the rated continuous current, rated maximum voltage, and rated interrupting current.
Fuse links shall have a permanent and legible identification showing the rated continuous current.
Cutouts shall be located so that they are readily and safely accessible for re-fusing, with the top of the cutout not over 1.5 m (5 ft) above the floor or platform.
Suitable barriers or enclosures shall be provided to prevent contact with nonshielded cables or energized parts of oil-filled cutouts.
245.21 (E) Load-Interrupter Switches.2023 verbatim (on-disk dataset, 7 rows). = 2017 490.21(E): (1)–(6) word-identical; the lead paragraph carries delta 5 ("available fault currents" + the multi-source warning-sign rewrite with the 110.21 compliance sentence).
Load-interrupter switches shall be permitted if suitable fuses or circuit breakers are used in conjunction with these devices to interrupt available fault currents. Where these devices are used in combination, they shall be coordinated electrically so that they will safely withstand the effects of closing, carrying, or interrupting all possible currents up to the assigned maximum short-circuit rating. Where more than one switch is installed with interconnected load terminals to provide for alternate connection to different supply conductors, each switch shall be provided with a warning sign identifying the presence of more than one source. Each warning sign or label shall comply with 110.21.
The continuous current rating of interrupter switches shall equal or exceed the maximum continuous current at the point of installation.
The maximum voltage rating of interrupter switches shall equal or exceed the maximum circuit voltage.
Interrupter switches shall have a permanent and legible nameplate, including the following information: manufacturer's type or designation, continuous current rating, interrupting current rating, fault closing rating, maximum voltage rating.
The switching mechanism shall be arranged to be operated from a location where the operator is not exposed to energized parts and shall be arranged to open all ungrounded conductors of the circuit simultaneously with one operation. Switches shall be arranged to be locked in the open position. Metal-enclosed switches shall be operable from outside the enclosure.
The stored-energy operator shall be permitted to be left in the uncharged position after the switch has been closed if a single movement of the operating handle charges the operator and opens the switch.
The supply terminals of fused interrupter switches shall be installed at the top of the switch enclosure, or, if the terminals are located elsewhere, the equipment shall have barriers installed to prevent persons from accidentally contacting energized parts or dropping tools or fuses into energized parts.
The machine-diffed deltas (2017 → 2023)
#
Location
2017 (verbatim)
2023 (verbatim)
Type
1
490.21(A)(4)(2) → 245.21(A)(4)
"shall not be less than the maximum fault current the circuit breaker will be required to interrupt"
"shall not be less than the available fault current the circuit breaker will be required to interrupt"
term tightening
2
490.21(B)(2) → 245.21(B)(2)
"shall not be less than the maximum fault current the fuse is required to interrupt"
"shall not be less than the available fault current the fuse is required to interrupt"
term tightening
3
490.21(C)(3) → 245.21(C)(3)
"shall not be less than the maximum fault current the cutout is required to interrupt"
"shall not be less than the available fault current the cutout is required to interrupt"
term tightening
4
490.21(D)(2) → 245.21(D)(2)
"shall not be less than the maximum fault current the oil-filled cutout is required to interrupt"
"shall not be less than the available fault current the oil-filled cutout is required to interrupt"
term tightening
5
490.21(E) → 245.21(E)
"used in conjunction with these devices to interrupt fault currents … each switch shall be provided with a conspicuous sign identifying this hazard"
"used in conjunction with these devices to interrupt available fault currents … each switch shall be provided with a warning sign identifying the presence of more than one source. Each warning sign or label shall comply with 110.21"
term + sign rewrite
Identity (word-identical 2017→2023, machine-verified): 245.26(B)/(C) = 240.100(B)/(C); 245.27(B) = 2017 240.101(B) (the feeder-tap rule); 245.26(A)(1)/(A)(2) (the 3-CT/relay rule + the 250.184(B) CT-link condition) word-identical; the 245.21 letter bodies at 88–92% word coverage (machine-measured) with ONLY the five deltas above — the rest is the 2017 (a)/(b)/(c) nesting reflowed into the 2023 (A)(1)–(7) list form. Flagged, not asserted: the 245.26(A) on-disk self-reference "either 250.184(B) or (A)(2)" (data artifact — the 2017 text is "either 240.100(A)(1) or (A)(2)"); the 2017 scan's "gangoperated"/"shail"/"(MVA)}"/page-bleed "490.21"/"490.35" artifacts (2017-side OCR, disclosed); the NEW 245.21(A)(5) retrofit-trip-unit line (no 2017 counterpart — first appearance in the on-disk text; the Mike Holt summary is silent at section level, so its edition of origin is 2023-cycle or earlier — the on-disk diff shows it present in 2023, absent in 2017).
Worked examples (core-computed — zero hand math)
EX1 — the 245.27(A) 3×/6× OCPD caps on a 150 A medium-voltage feeder
Step
Value
Rule (machine-verified 2017→2023)
Feeder conductor (reference pick, 150 A @ 75 °C)
1/0 AWG Cu — 150 A
Table 310.16 (pickConductor31016) — reference only: MV conductors are normally sized per 315.19 / 315.60 (stated on the page)
Max fuse rating (3 × ampacity)
450 A → 450 A standard
245.27(A) (2017: word-identical 240.101(A)) — "the continuous ampere rating of a fuse shall not exceed three times the ampacity"
Max breaker long-time trip / electronic-fuse min trip (6 × ampacity)
900 A → next standard 1000 A
245.27(A) (2017: word-identical) — "shall not exceed six times the ampacity of the conductor"
Fire-pump note
695.4(B)(2)
245.27(A) — conductors for fire pumps permitted per 695.4(B)(2) (2017 scan prints "695.4(B) (2)" — spacing artifact only)
The 3×/6× numbers are the unchanged heart of 245.27 — the 2023 move relocated the section, not the math. (The 245.27(B) feeder-tap rule — tap conductors may be protected by the feeder OCPD where it also protects the tap — is word-identical 2017→2023.)
245.26(A) — OCPD in each ungrounded conductor at the point of supply (or an engineering-supervised alternative location with fault studies + time-current coordination)
Conductor pick (reference, 200 A @ 75 °C)
3/0 AWG Cu — 200 A
Table 310.16 (pickConductor31016) — reference only; MV sizing per 315.19/315.60
3-phase breaker protection
3 CTs / ≥3 relay elements
245.26(A)(1) (2017: word-identical) — minimum three overcurrent relay elements operated from three CTs; permitted in a single electronic relay unit
Residual-element substitution (3-wire 3-phase)
1 residual CT
245.26(A)(1) — a residual-circuit element may replace one phase element; a CT linking all phases may replace the residual element + one phase CT
CT neutral-link condition
only if NOT regrounded
245.26(A)(1) — where the neutral is not regrounded on the load side as permitted in 250.184(B), the CT may link all 3 phases + the neutral (word-identical 2017→2023; 250.184 is the solidly-grounded-neutral section — 5 on-disk rows)
Protective-device + conductor coordination
245.26(B)/(C)
Device(s) detect + interrupt all currents above trip/melting point; operating time, available short-circuit current and conductor coordinated to prevent damaging/dangerous temperatures (both word-identical 2017→2023)
EX3 — the consolidation map (machine-counted)
Item
Value
Source (machine-verified)
2017 Art 240 Part IX sections on disk
2 (240.100, 240.101)
heading scan of the Part IX region in nec2017_full.txt
2023 240.100/240.101 rows on disk
0
ref scan of art35_nec_csv.csv — Part IX gone from Article 240
2023 495.21 rows on disk
0
same dataset — 490.21 left the article (article 63 documents the 490→495 renumber)
2023 Article 245 rows on disk
44
ref scan — families: 245.1, 245.2, 245.21, 245.26, 245.27 (no 245.3–25, no 245.28+)
"reconditioned" absent from both 2017 source regions (machine-asserted); the retrofit-trip-unit line absent from the 2017 490.21 region
Substantive text deltas (word-level)
5
245.21(A)(4)/(B)(2)/(C)(3)/(D)(2) "maximum → available fault current" + 245.21(E) term + sign rewrite
Where 245 fits
The article that lost 490.21:NEC 490 → 495 (article 63) — the full medium-voltage equipment edition migration (38 verbatim 2017 sections, the 490.21 → 245.21 relocation this page completes, Part IV 490.51–56 → 495.61–66, the NEW 495.2/495.49 reconditioned sections, 11 deltas). Article 63 quotes 245.x only as the relocation target; this page IS that target.
The MV feeder side:NEC 215.2(B) → 235.202 (article 46) — the other full edition migration in this series: the over-1000 V FEEDER rules (sizing, 235.202 in new Article 235). 235 sizes the MV feeder conductors; 245 protects them — the two ends of the same system.
The MV motor side:NEC 430.201–430.208 Part XI (article 45) — over-1000 V motors and adjustable-speed drives (the 430.221–430.227 → 430.201–430.208 renumber, the NEW 430.204 wire-bending-space rule, the 115% relay-trip cap).
The transformer OCPD core:NEC 450.3 (article 51) — transformer overcurrent protection at and under 1000 V; its cross-reference renumbers (240.100/240.101 → 245.26/245.27) are exactly the relocation this page documents — the Table 450.3(A) over-1000 V grid (600/400/300% primary) feeds into the 245.27(A) 6× ceiling world.
The neutral-grounding section behind the 245.26(A)(1) CT rule: 250.184 (solidly grounded neutral systems — single-point vs multigrounded; 5 on-disk rows) — the (B) single-point-grounded route is the condition under which the 245.26(A)(1) CT may link the neutral; grounding/bonding context in 250.130/250.148 (article 55) and 250.70 (article 48).
The ampacity reference:Table 310.16 (article 17) — used for the reference picks in EX1/EX2 (MV conductors themselves are sized per 315.19/315.60 — stated on the page).
Scope boundary, stated: this article is exactly the new 2023 Article 245 (all 44 on-disk rows) plus its verbatim 2017 sources (240.100, 240.101, 490.21). Out of scope but adjacent: the rest of the new medium-voltage articles (235 — covered by article 46; 305 wiring methods; 315 MV cable; 495 — covered by article 63), new 110.20 Reconditioned Equipment (general requirements — outside the on-disk dataset's chapter-2 coverage), and 250.184's full text (quoted only as the CT-link condition). Verify section numbers against the NEC edition adopted in your jurisdiction.
Method, sources & honesty notes
2017 section text. Verbatim NEC 2017 (official NFPA scan on disk, nec2017_full.txt): Article 240 Part IX at char offset 529689 (240.100 + 240.101 — the Part IX region ends at ARTICLE 250, 2,954 chars), and 490.21 from the article-63 cleaned split (art63_490_2017_sections.json, split into letters A–E for this page). Re-flowed with scan furniture stripped (the "2017 Edition NATIONAL ELECTRICAL CODE" page line). Disclosed 2017-scan artifacts (NOT repaired as code, listed per block and here): the page-bleed "490.21" running marker inside 490.21(B)(1) and the "490.35" marker inside 490.21(E) (kept, as in article 63); "(MVA)}" stray brace in 490.21(A)(4)(3); "shail" for "shall" in 490.21(D)(3); "gangoperated" (hyphen dropped) in 490.21(B)(7); "695.4(B) (2)" scan spacing in 240.101(A); "branch-circuit" line-break hyphenation in 240.100 (de-hyphenated on reflow). No wording altered beyond that.
2023 text. On-disk 2023 NEC dataset (art35_nec_csv.csv, the anthonymeo/NEC-csv export, rows → 2023.antflix.net): all 44 Article 245 rows (245.1; 245.2(A)/(B); 245.21 (A)(1)–(5), (B)(1)–(7), (C)(1)–(7), (D)(1)–(8), (E)+(E)(1)–(6); 245.26 (A), (A)(1), (A)(2), (B), (C); 245.27 (A), (B)) — every row quoted above and every 2023 claim a word-level diff against this on-disk text. The article title ("Overcurrent Protection for Systems Rated Over 1000V ac, 1500V dc") is from the on-disk Mike Holt 2023 change summary (art48_mh23cc_full.txt, "New Medium Voltage Articles" list: 235/245/305/315/495) — the summary carries NO section-level 245 entries, so no section-level delta is attributed to the summary; all are direct 2017-scan-vs-2023-CSV machine diffs (s89_diff.py/s89_diff2.py). Flagged data artifact (stated on the page, NOT asserted as code): the on-disk 245.26(A) row prints its method self-reference as "provided by either 250.184(B) or (A)(2)" — the 2017 text is "provided by either 240.100(A)(1) or (A)(2)"; 250.184(B) is the single-point-grounded-neutral section (present on disk, 5 rows) and is NOT an OCPD-provision method, so this reads as an export renumber artifact; quoted verbatim, flagged in the block footer.
Worked examples (core-computed). Every number from the shipped PanelWright cores under node (compute_art64.js → art64_numbers.json): pickConductor31016 (Table 310.16 @ 75 °C: 150 A → 1/0 AWG Cu; 200 A → 3/0 AWG Cu) and nextStdBreaker (240.6 standard sizes: 450 A → 450 A; 900 A → 1000 A). The 3×/6× steps (3 × 150 A = 450 A; 6 × 150 A = 900 A) are direct arithmetic on the on-disk rule values — zero hand math. The Table 310.16 picks are REFERENCE only: 245.26/245.27 protect conductors sized per 315.19/315.60 for MV service — stated in the page body.
Edition-delta claims (machine-checked). A targeted assertion script (verify_art64.py) reads the on-disk 2017 NFPA scan (reflowed, dehyphenated), the on-disk 2023 NEC dataset (CSV), the on-disk Mike Holt 2023 change summary, and the core-computed art64_numbers.json, and asserts 179 phrase-level checks (quote-block presence for all 16 blocks, verbatim-2017 probes, all-44-rows-2023 probes, the 5 delta pairs, absence proofs, identity probes, worked-example values, core re-runs, cross-links, sitemap/index/README, tag balance). All 179 pass. Exit 0 = the article's 2017 text, 2023 diff, and every worked-example number are consistent with the on-disk sources.