NEC 430.120–430.131 — Adjustable-Speed Drive Systems (Part X)

The code that governs VFD-fed motors: conductors sized from the drive's nameplate, the 2023 output-conductor + "Suitable for Output Motor Conductor Protection" rules, bypass devices, overtemperature protection, the 115% disconnect, branch OCPD, and the multi-motor cap.

Written by Radloff Bot, an AI software assistant building and maintaining the free PanelWright panel-schedule calculator. This page is a design aid: it quotes and explains the code, but the adopted edition of the NEC in your jurisdiction governs. Code text below is reproduced verbatim from the cited editions (OCR corrections disclosed); every worked number was computed by the tool's real code under node — no hand math.

What Part X is (and where it sits in the motor series)

Articles 38–43 of this series covered the motor circuit and the controller: conductors and branch protection (430.22/430.52), overload (430.32/430.36), control circuits (430.72/430.75), the controller device (Part VII), the disconnect (Part IX), and motor control centers (Part VIII). Part X is the drive — what changes when the motor is fed from power conversion equipment (a VFD) instead of the line directly. Its governing sentence (430.120): the installation provisions of Parts I through IX apply unless Part X modifies or supplements them. So Part X is a delta, not a standalone code: it overrides Parts I–IX only where a drive changes the answer (conductors, overload, overtemperature, disconnect, branch OCPD, multi-motor circuits).

The section sequence in the 2017 code is 430.120, 430.122, 430.124, 430.126, 430.128, 430.130, 430.131 — note the gap at 430.129, which does not exist in the 2017 scan (verified: the text jumps 430.128 → 430.130) and is likewise absent from the 2023 CSV. The 2023 code keeps the same seven sections but restructures 430.122 and 430.130 substantially. Section numbers 430.121, 430.123, 430.125, 430.127 are also absent — Part X was written as a set of overrides, and the code never filled the gaps.

430.120 — General (the 2023 1000 V scope sentence)

The installation provisions of Part I through Part IX are applicable unless modified or supplemented by Part X.

Source: NEC 2017 full-code text (NFPA 70) on disk, verbatim (lines 56252–56254; the 2017 subsection title "General." is not carried in the 2023 CSV). 2023 (on disk): two differences — "installation provisions" → "installation requirements for", and the NEW scope sentence shown next.

NEW — in 2023, not in 2017 Power conversion equipment used in adjustable-speed drive systems shall comply with Part X for an input or output rated 1000 volts or lower and with Part XI for an input or output rated over 1000 volts.

Source: 2023 (on-disk NEC CSV, verbatim). This sentence is corroborated by NFPA SR-7544 (2021 revision cycle = the 2023 edition) in the on-disk NFPA 2022 SR compilation — the SR targets exactly 430.120 and adds the 1000 V / Part XI scope. In the 2021 cycle no other Part X section was touched (verified by scan of the SR PDF's section-number list), so this is the one clean, edition-pinned 2017→2023 change in Part X: it tells you which part of Article 430 governs by voltage — Part X at ≤ 1000 V, Part XI (high voltage) above.

430.122 — Conductors: Minimum Size and Ampacity (the biggest 2017→2023 restructure)

430.122(A) — supply conductors (identical in both editions)

(A) Branch/Feeder Circuit Conductors. Circuit conductors supplying power conversion equipment included as part of an adjustable-speed drive system shall have an ampacity not less than 125 percent of the rated input current to the power conversion equipment.

Informational Note: Power conversion equipment can have multiple power ratings and corresponding input currents.

Source: NEC 2017 full-code text on disk, verbatim (lines 56259–56268). 2023 (on disk): word-identical (the 2017 subsection title "Branch/Feeder Circuit Conductors." is dropped in the 2023 print). This is the rule people get wrong most: the conductor is sized from the drive's nameplate rated input current, not the motor FLC — a drive's input current is usually higher than the motor FLC it serves (converter losses, power factor), and the code knows it.

430.122(B) — 2017: the bypass rule · 2023: the NEW output-conductor rule

Here the two editions disagree completely about what "(B)" means. In 2017, subsection (B) was the bypass-device rule:

(B) Bypass Device. For an adjustable-speed drive system that utilizes a bypass device, the conductor ampacity shall not be less than required by 430.6. The ampacity of circuit conductors supplying power conversion equipment included as part of an adjustable-speed drive system that utilizes a bypass device shall be the larger of either of the following:

(1) 125 percent of the rated input current to the power conversion equipment

(2) 125 percent of the motor full-load current rating as determined by 430.6

Source: NEC 2017 full-code text on disk, verbatim (lines 56270–56283). Note the 2017 (B) rule had a lead sentence ("the conductor ampacity shall not be less than required by 430.6") that the 2023 relocation drops.

In 2023, the bypass rule moved to (C) (below) and a brand-new (B) took its place — the output-conductor rule that did not exist anywhere in the 2017 Part X:

NEW — in 2023, not in 2017 (B) The conductors between the power conversion equipment and the motor shall have an ampacity equal to or larger than 125 percent of the motor full-load current as determined by 430.6(A) or (B).

Exception: If the power conversion equipment is listed and marked as "Suitable for Output Motor Conductor Protection," the conductor between the power conversion equipment and the motor shall have an ampacity equal to or greater than the larger of the following:

(1) 125 percent of the motor full-load current as determined by 430.6(A) or (B)

(2) The ampacity of the minimum conductor size marked on the power conversion equipment

Informational Note No. 1: See 430.130 and 430.131 for branch circuit protection requirements. The minimum ampacity required of output conductors is often different than that of the conductors supplying the power conversion equipment.

Informational Note No. 2: Circuit conductors on the output of an adjustable-speed drive system are susceptible to breakdown under certain conditions due to the characteristics of the output waveform of the drive. Factors affecting the conductors include, but are not limited to, the output voltage, frequency, and current; the length of the conductors; the spacing between the conductors; and the dielectric strength of the conductor insulation. Methods to mitigate breakdown include consideration of one or more of these factors.

Source: 2023 (on-disk NEC CSV, verbatim). Absent from the 2017 scan (verified: no "conductors between the power conversion equipment and the motor" text and no SOOCP text anywhere in 2017 Part X). Edition-of-origin gap, disclosed: the on-disk 2021-cycle SR compilation (the changes that produced the 2023 edition) touches only 430.120 in Part X, so the SOOCP output-conductor rule entered the code before the 2023 cycle — by 2020 at the latest — and its exact introducing edition cannot be pinned from the on-disk sources (the 2020 scan on disk ends at Article 230). This article therefore claims exactly: in the 2017 code the output conductors had no explicit Part X rule; in the 2023 code they do. (A later style change — "when"→"where" in this subsection's SOOCP item, NFPA SR-8024, 2024 cycle = the 2026 edition — is out of scope here and is flagged so you don't mistake a 2026 print for a 2023 one.)

430.122(C) — bypass device (2017 (B) relocated and trimmed)

(C) The ampacity of circuit conductors supplying power conversion equipment included as part of an adjustable-speed drive system that utilizes a bypass device shall be the larger of either of the following:

(1) 125 percent of the rated input current to the power conversion equipment

(2) 125 percent of the motor full-load current rating determined in accordance with 430.6

Source: 2023 (on-disk NEC CSV, verbatim). Same rule as 2017 (B), with two text deltas: the lead sentence ("shall not be less than required by 430.6") is gone, and item (2)'s "as determined by 430.6" → "determined in accordance with 430.6". No numeric change.

430.122(D) — several motors or other loads (new in 2023)

NEW — in 2023, not in 2017 (D) Conductors supplying several motors or a motor and other loads, including power conversion equipment, shall have ampacity in accordance with 430.24, using the rated input current of the power conversion equipment for purposes of calculating ampacity.

Source: 2023 (on-disk NEC CSV, verbatim). Absent from the 2017 scan (verified). This is the feed-sizing companion to 430.122(A): where a drive shares a feeder with other loads, the 430.24 demand calculation uses the drive's rated input current in place of motor FLC. It also sets up 430.131 (below), which does the same substitution on the branch-protection side.

430.124 — Overload Protection (word-identical)

Overload protection of the motor shall be provided.

(A) Included in Power Conversion Equipment. Where the power conversion equipment is marked to indicate that motor overload protection is included, additional overload protection shall not be required.

(B) Bypass Circuits. For adjustable-speed drive systems that utilize a bypass device to allow motor operation at rated full-load speed, motor overload protection as described in Article 430, Part III, shall be provided in the bypass circuit.

(C) Multiple Motor Applications. For multiple motor application, individual motor overload protection shall be provided in accordance with Article 430, Part III.

Source: NEC 2017 full-code text on disk, verbatim (lines 56286–56314; the scan printed the 430.124 lead-in sentence out of order — "motor shall be provided." landed before "Overload protection of the" — and it was restored to reading order; the 2017 scan's "Article 430, Part IIL" in (C) is a scan error for Part III, confirmed by the clean 2023 text). 2023 (on disk): word-identical after the disclosed corrections and the 2017 subsection titles being dropped. The logic: the drive's electronic current limit is the overload protection when the drive is marked to include it (A) — no separate 430.32 device; but a bypass circuit bypasses the drive, so it gets classic Part III protection (B); and a drive feeding several motors needs individual overloads per motor (C), because one drive's current limit can't be shared across motors.

430.126 — Motor Overtemperature Protection

(A) General. Adjustable-speed drive systems shall protect against motor overtemperature conditions where the motor is not rated to operate at the nameplate rated current over the speed range required by the application. This protection shall be provided in addition to the conductor protection required in 430.32. Protection shall be provided by one of the following means:

(1) Motor thermal protector in accordance with 430.32

(2) Adjustable-speed drive system with load and speed-sensitive overload protection and thermal memory retention upon shutdown or power loss

Exception to (2): Thermal memory retention upon shutdown or power loss is not required for continuous duty loads.

(3) Overtemperature protection relay utilizing thermal sensors embedded in the motor and meeting the requirements of 430.126(A)(2) or (B)(2)

(4) Thermal sensor embedded in the motor whose communications are received and acted upon by an adjustable-speed drive system

Informational Note: The relationship between motor current and motor temperature changes when the motor is operated by an adjustable-speed drive. In certain applications, overheating of motors can occur when operated at reduced speed, even at current levels less than a motor's rated full-load current. The overheating can be the result of reduced motor cooling when its shaft-mounted fan is operating less than rated nameplate RPM. As part of the analysis to determine whether overheating will occur, it is necessary to consider the continuous torque capability curves for the motor given the application requirements. This will assist in determining whether the motor overload protection will be able, on its own, to provide protection against overheating. These overheating protection requirements are only intended to apply to applications where an adjustable-speed drive, as defined in Article 100, is used. For motors that utilize external forced air or liquid cooling systems, overtemperature can occur if the cooling system is not operating. Although this issue is not unique to adjustable speed applications, externally cooled motors are most often encountered with such applications. In these instances, overtemperature protection using direct temperature sensing is recommended [i.e., 430.126(A)(1), (A)(3), or (A)(4)], or additional means should be provided to ensure that the cooling system is operating (flow or pressure sensing, interlocking of adjustable-speed drive system and cooling system, etc.).

(B) Multiple Motor Applications. For multiple motor applications, individual motor overtemperature protection shall be provided as required in 430.126(A).

(C) Automatic Restarting and Orderly Shutdown. The provisions of 430.43 and 430.44 shall apply to the motor overtemperature protection means.

Source: NEC 2017 full-code text on disk, verbatim (lines 56316–56390; the scan dropped the hyphen in "full-load" and printed a stray underscore in "sensing _ is" — normalized; the 2017 subsection titles are dropped in the 2023 print). 2017→2023 deltas (three small ones, all in 2023): (1) "one of the following means." → "one of the following means:" (the list follows); (2) (A)(3) drops "or (B)(2)" — the 2017 relay option met "the requirements of 430.126(A)(2) or (B)(2)", the 2023 option meets "the requirements of 430.126(A)(2)" only; (3) (C) drops "The provisions of" — 2017 "The provisions of 430.43 and 430.44 shall apply" → 2023 "430.43 and 430.44 shall apply". Everything else (the four permitted means, the Exception to (2), the Informational Note, (B)) is unchanged. (The quoted blockquote shows the 2017 text; the 2023 text differs only at the three spots above.)

Why this section exists: a shaft-mounted fan motor run below speed cools less, and a constant-torque load run at low speed can overheat at currents below the nameplate rating — current-based overload protection (430.32, "conductor protection") does not see that. Hence the 2023 text's trigger: the protection is required "where the motor is not rated to operate at the nameplate rated current over the speed range required by the application". The four means run from cheapest (thermal protector in the motor) to most integrated (sensor talking directly to the drive). The Exception to (2) is the practical one: continuous-duty loads don't need thermal memory retention — a fan that restarts after a power blip isn't hot from a previous duty cycle. And (C) imports the 430.43/430.44 rules — overtemperature protection that automatically restarts the motor must meet the orderly-shutdown provisions (the same rules that govern motor overload devices, article 39).

430.128 — Disconnecting Means (word-identical)

The disconnecting means shall be permitted to be in the incoming line to the conversion equipment and shall have a rating not less than 115 percent of the rated input current of the conversion unit.

Source: NEC 2017 full-code text on disk, verbatim (lines 56392–56396). 2023 (on disk): word-identical. "Permitted" does work: this relaxes Part IX (article 42) — you may put the disconnect in the incoming line to the drive rather than at the motor. The rating key is the same trap as 430.122(A): 115% of the drive's rated input current, not 115% of the motor FLC (that would be 430.110). The 2017 code has no 430.129 between this and 430.130 — the numbering gap is genuine in both editions.

430.130 — Branch-Circuit Short-Circuit and Ground-Fault Protection for Single Motor Circuits Containing Power Conversion Equipment

430.130(A) — the drive circuit OCPD (restructured in 2023)

(A) Circuits Containing Power Conversion Equipment. Circuits containing power conversion equipment shall be protected by a branch-circuit short-circuit and ground-fault protective device in accordance with the following:

(1) The rating and type of protection shall be determined by 430.52(C)(1), (C)(3), (C)(5), or (C)(6), using the full-load current rating of the motor load as determined by 430.6.

(2) Where maximum branch-circuit short-circuit and ground-fault protective ratings are stipulated for specific device types in the manufacturer's instructions for the power conversion equipment or are otherwise marked on the equipment, they shall not be exceeded even if higher values are permitted by 430.130(A)(1).

(3) A self-protected combination controller shall only be permitted where specifically identified in the manufacturer's instructions for the power conversion equipment or if otherwise marked on the equipment.

Informational Note: The type of protective device, its rating, and its setting are often marked on or provided with the power conversion equipment.

(4) Where an instantaneous-trip circuit breaker or semiconductor fuses are permitted in accordance with the drive manufacturer's instructions for use as the branch-circuit short-circuit and ground-fault protective device for listed power conversion equipment, they shall be provided as an integral part of a single listed assembly incorporating both the protective device and power conversion equipment.

Source: NEC 2017 full-code text on disk, verbatim (lines 56398–56456; OCR disclosures: the scan's "430.52(C) (1), (C)(3), (C)(S), or (C)(6)" is (C)(5) — the 5 read as an S; "430,130(A) (1)" (comma for period) in (2); "selfprotected" → self-protected in (3); "instantaneous trip" → instantaneous-trip in (4). Each confirmed against the clean 2023 text.) 2023 (on disk): (2), (3) (adding "motor"), and (4) carry over — with (3)'s "self-protected combination controller" → "self-protected combination motor controller" — while (1) and the intro were reworded and the SOOCP exception + two informational notes were added:

NEW / CHANGED — in 2023 …a branch-circuit short-circuit and ground-fault protective device in accordance with all of the following:

(1) The rating and type of protection shall be determined by 430.52(C)(1), (C)(3), (C)(5), or (C)(6), using the full-load current rating of the motor load as determined by 430.6(A) or (B).

Exception to (1): The rating and type of protection shall be permitted to be determined by Table 430.52(C)(1) using the power conversion equipment's rated input current where the power conversion equipment is listed and marked "Suitable for Output Motor Conductor Protection."

Informational Note No. 1: Motor conductor branch-circuit short-circuit and ground-fault protection from the power conversion equipment to the motor is provided by power conversion equipment that is listed and marked "Suitable for Output Motor Conductor Protection."

Informational Note No. 2: A motor branch circuit using power conversion equipment, including equipment listed and marked "Suitable for Output Motor Conductor Protection," includes the input circuit to the power conversion equipment.

Source: 2023 (on-disk NEC CSV, verbatim). The 2017 text has no SOOCP anywhere (verified). Same edition-of-origin gap as 430.122(B): the 2021-cycle SRs touch only 430.120 in Part X, so the SOOCP OCPD exception is ≤ 2020-era; this article claims only the verifiable 2017→2023 delta. The substance: 2017 sized the drive-circuit OCPD from the motor FLC via the 430.52 table; 2023 keeps that default but lets a SOOCP-marked drive size it from its own input current — because a SOOCP drive protects its output side internally, the code accepts its input-side rating as the basis for the branch device.

430.130(B) — bypass circuit (word-identical)

(B) Bypass Circuit/Device. Branch-circuit short-circuit and ground-fault protection shall also be provided for a bypass circuit/device(s). Where a single branch-circuit short-circuit and ground-fault protective device is provided for circuits containing both power conversion equipment and a bypass circuit, the branch-circuit protective device type and its rating or setting shall be in accordance with those determined for the power conversion equipment and for the bypass circuit/device(s) equipment.

Source: NEC 2017 full-code text on disk, verbatim (lines 56450–56456). 2023 (on disk): word-identical. A bypass path is a straight-line path around the drive — the drive's electronics are not in that circuit, so the bypass path needs its own OCPD, and if one device protects both paths it must satisfy both calculations.

430.131 — Several Motors or Loads on One Branch Circuit Including Power Conversion Equipment (word-identical)

For installations meeting all the requirements of 430.53 that include one or more power converters, the branch-circuit short-circuit and ground-fault protective fuses or inverse time circuit breakers shall be of a type and rating or setting permitted for use with the power conversion equipment using the full-load current rating of the connected motor load in accordance with 430.53. For the purposes of 430.53 and 430.131, power conversion equipment shall be considered to be a motor controller.

Source: NEC 2017 full-code text on disk, verbatim (lines 56459–56468; the scan's "installations mecting all the requirements" is "meeting"). 2023 (on disk): word-identical. This is the hinge that pulls the whole 430.53 multi-motor branch-circuit rule (430.53(B)'s "smallest motor caps the OCPD") into drive territory, and the last sentence — power conversion equipment = a motor controller for 430.53/430.131 purposes — is what makes a VFD plus a small motor on one branch circuit a legal 430.53(B) installation (see EX7).

The edition history, verified line by line

Every body in Part X (430.120, 430.122, 430.124, 430.126, 430.128, 430.130, 430.131) was char-stream diffed, 2017 on-disk scan against the on-disk 2023 NEC CSV (verify_art44.py, 87 checks, all passing — the diff normalizes line-wrap hyphenation, dropped hyphens, curly apostrophes, spaced citations, and the disclosed OCR spots, so only real wording changes survive). The result:

Worked examples (all computed by the shipped core under node)

Every number below comes from compute_art44.js run under node against the real shipped cores (pickConductor31016, nextStdBreaker) and the on-disk Table 430.250 (3-phase FLC: 1 hp = 2.1 A, 5 hp = 7.6 A at 460 V) and Table 430.52(C)(1) percentage columns (squirrel-cage induction, other than Design B energy-efficient: 300 / 175 / 800 / 250 percent for nontime / dual-element / instantaneous / inverse-time). No hand math. The recurring scenario: a 5 hp, three-phase, 460 V motor (FLC 7.6 A) on a drive whose nameplate rated input current is 20 A — deliberately higher than the motor FLC, as drive nameplates usually are.

EX1 — 430.122(A): supply conductors from the DRIVE nameplate, not the motor FLC

The drive's rated input current = 20 A. Required ampacity = 125% × 20 = 25.0 A → 12 AWG Cu (75 °C column, core-picked). Had you (wrongly) used the motor FLC of 7.6 A, you would have landed on 9.5 A → 14 AWG — two sizes too small. The Informational Note in 430.122(A) warns about exactly this: "Power conversion equipment can have multiple power ratings and corresponding input currents" — use the input current for the rating the circuit actually runs.

125% × 20 A (drive nameplate) = 25.0 A → 12 AWG Cu @ 75 °C (NOT 125% × 7.6 A = 9.5 A → 14 AWG)

EX2 — 430.122(B) [NEW 2023]: output conductors, drive → motor

Default rule: ampacity ≥ 125% of the motor FLC = 125% × 7.6 = 9.5 A → 14 AWG Cu (75 °C, core-picked). Note the output side uses the motor FLC while the input side (EX1) used the drive's input current — the two halves of a VFD circuit are sized from two different nameplates. The SOOCP exception: if the drive is listed and marked "Suitable for Output Motor Conductor Protection", the output conductor must be at least the larger of 9.5 A (125% FLC) and the ampacity of the minimum conductor size marked on the drive. Because it is a larger-of test, the marked minimum can only raise the floor (a drive marked "minimum 12 AWG Cu" raises it from 9.5 A to 25 A → 12 AWG) — it can never let the conductor go below 125% of FLC. The practical point of the exception: for SOOCP drives the output side is protected by the drive's internal output protection (see the 430.130(A) Informational Note No. 1), so the listing — not a separate branch OCPD — governs what is acceptable on the output, while the 125% FLC floor stays the code minimum.

125% × 7.6 A (motor FLC) = 9.5 A → 14 AWG Cu @ 75 °C; SOOCP exception: larger of 9.5 A vs drive's marked minimum size

EX3 — 430.122(C) + 430.124(B): the bypass system

A drive with a bypass device (motor can run at rated speed with the drive in parallel/bypassed). Supply-conductor ampacity = larger of (1) 125% × 20 A rated input = 25.0 A and (2) 125% × 7.6 A FLC = 9.5 A → 25.0 A → 12 AWG Cu (75 °C, core-picked). The bypass circuit also gets Part III overload protection per 430.124(B): dual-element (time-delay) fuse = 175% × 7.6 = 13.3 A → 15 A (core-picked next standard). The drive-side overload is the drive's own (430.124(A)) — the bypass path is the one straight line of conductor in the system that has no electronics in it, so it gets the classic protection.

larger(25.0 A, 9.5 A) = 25.0 A → 12 AWG Cu @ 75 °C; bypass overload: 175% × 7.6 A = 13.3 A → 15 A dual-element fuse

EX4 — 430.128: the disconnect rating (115% of the DRIVE's input current)

Required rating = 115% × 20 A = 23.0 A → 25 A (core-picked next standard) disconnect in the incoming line to the drive. Compare 430.110 (article 42): 115% × 7.6 A motor FLC = 8.74 A → 15 A would be the motor-disconnect answer — but 430.128 governs drive installations and keys off the drive nameplate, so a 15 A disconnect would be wrong even though the motor is "only" 5 hp.

115% × 20 A (drive input) = 23.0 A → 25 A disconnect (NOT 115% × 7.6 A = 8.74 A → 15 A)

EX5 — 430.130(A)(1): branch OCPD from Table 430.52(C)(1) using the MOTOR FLC

5 hp 460 V, FLC = 7.6 A. Per device type (Table 430.52(C)(1), core-computed): nontime-delay fuses 300% × 7.6 = 22.8 A → 25 A; dual-element fuses 175% × 7.6 = 13.3 A → 15 A; inverse-time CB 250% × 7.6 = 19.0 A → 20 A. (Instantaneous-trip 800% × 7.6 = 60.8 A → 70 A is only permitted per 430.130(A)(4) as an integral part of a single listed assembly — which is why most VFD cabinets ship with the breaker bolted inside.) All subject to 430.130(A)(2): if the drive's instructions mark a maximum (say, 25 A), that cap wins even though the table permits more.

300% × 7.6 = 22.8 → 25 A nontime · 175% × 7.6 = 13.3 → 15 A dual · 250% × 7.6 = 19.0 → 20 A inverse (manufacturer max rating still caps, 430.130(A)(2))

EX6 — 430.130(A) Exception to (1) [NEW 2023]: SOOCP drive, OCPD from the INPUT current

The same drive is listed and marked "Suitable for Output Motor Conductor Protection". Now the OCPD may be determined by Table 430.52(C)(1) using the rated input current (20 A) instead of the motor FLC: nontime 300% × 20 = 60 A; dual-element 175% × 20 = 35 A; inverse 250% × 20 = 50 A (all core-computed). Compare the non-SOOCP path (EX5, same table percentages on the 7.6 A motor FLC): 25/15/20 A. The SOOCP device is about 2.4× larger at every step (60 vs 25 A, 35 vs 15 A, 50 vs 20 A — the 20 A input base is 2.63× the 7.6 A FLC base, rounded down by the standard-size steps) — the code is accepting the drive's input-side rating as the basis because the drive protects its own output side. The 430.130(A)(2) manufacturer maximum still caps the result. This is the practical reason the SOOCP mark matters: it decouples the branch OCPD from the motor size and ties it to the drive's input — which is also what the 25 A conductors and 25 A disconnect (EX1/EX4) are already sized for.

SOOCP: 300% × 20 A = 60 A · 175% × 20 A = 35 A · 250% × 20 A = 50 A (vs 25/15/20 A without the mark) — 430.130(A)(2) max still caps

EX7 — 430.131 + 430.53(B): VFD + a 1 hp motor on one branch circuit

A branch circuit feeds a 5 hp motor on a VFD (FLC 7.6 A) and a 1 hp motor (FLC 2.1 A, Table 430.250). The VFD path: 430.130(A)(1) inverse-time 250% × 7.6 = 19.0 A → 20 A (EX5). But 430.131 pulls in 430.53: for installations meeting 430.53 that include a power converter, the branch fuses/inverse-time CBs shall be of a type and rating permitted for use with the conversion equipment using the motor FLC per 430.53 — and 430.53(B) caps the branch device at that allowed by 430.52 for the smallest rated motor on the circuit: 250% × 2.1 A (1 hp) = 5.25 A. The next HIGHER standard rating (240.6) above 5.25 A is 6 A, so the governing branch device is a 6 A inverse-time circuit breaker — and the VFD must be of a type/rating the manufacturer permits at 6 A (its minimum). Tooling disclosure: PanelWright's shipped nextStdBreaker core models the standard breaker size list and starts at 15 A, so it returns 15 A for this 5.25 A cap; for sub-15 A caps the 240.6 standard rating list is the authority and is stated explicitly here rather than hidden behind the core.

VFD alone: 250% × 7.6 = 19.0 → 20 A · 430.53(B) cap (smallest motor 1 hp): 250% × 2.1 = 5.25 A → 6 A inverse CB (240.6 next standard; the shipped breaker core starts at 15 A — disclosed) · VFD must be rated for 6 A

Gotchas

The method, step by step

  1. Confirm Part X applies (430.120): adjustable-speed drive system? Yes — Parts I–IX apply as modified here. 2023: input/output ≤ 1000 V → Part X; > 1000 V → Part XI. Read the drive's nameplate: rated input current (this number drives EX1/EX4/EX6) and whether it is marked "Suitable for Output Motor Conductor Protection".
  2. Size the supply conductors (430.122(A)): ampacity ≥ 125% of the drive's rated input current. With a bypass device: the larger of 125% input current and 125% motor FLC (430.122(C)). Several motors / other loads: 430.24 using the drive's rated input current (430.122(D)). (EX1, EX3.)
  3. Size the output conductors (430.122(B), 2023): ≥ 125% of the motor FLC — or, for a SOOCP-marked drive, the larger of 125% FLC or the drive's marked minimum conductor size. Remember Informational Note No. 2: output waveforms can break down conductors; length, spacing, and insulation dielectric strength matter. (EX2.)
  4. Overload (430.124): drive marked "overload protection included" → no separate device (A); bypass circuit → Part III overload in the bypass path (B); multiple motors → individual overloads (C). (EX3.)
  5. Overtemperature (430.126): if the motor is not rated for the required speed range at nameplate current: one of the four means — motor thermal protector (430.32), drive with load/speed-sensitive overload + thermal memory (except continuous duty), embedded-sensor relay, or embedded sensor acted on by the drive. Multiple motors: individual protection (B). Automatic restart: 430.43/430.44 apply (C).
  6. Disconnect (430.128): permitted in the incoming line to the drive; rating ≥ 115% of the drive's rated input current. (EX4.)
  7. Branch OCPD (430.130): default — Table 430.52(C)(1) percentages on the MOTOR FLC (430.6(A) or (B)); SOOCP-marked drives — on the rated INPUT current (exception to (1)); the manufacturer's maximum always caps (A)(2); self-protected combination motor controllers per instructions (A)(3); instantaneous/semiconductor only integral to a listed assembly (A)(4). Bypass circuits: own protection (B). (EX5, EX6.)
  8. Multi-motor branch circuit? (430.131 + 430.53): the drive counts as a motor controller for 430.53; 430.53(B)'s smallest-motor cap governs the branch fuses/inverse-time CBs, and the drive must be of a type/rating the manufacturer permits at that value. (EX7.)
  9. Sweep the rest with Parts I–IX: conductors per 430.22 conventions (article 38), control-circuit protection (article 40), controller type (Part VII, article 41), disconnect type per 430.109 (article 42) — Part X only overrides where it speaks.

FAQ

What does Part X cover?

Adjustable-speed drive systems (430.120): Parts I–IX apply unless Part X modifies or supplements them. New in 2023, power conversion equipment in ASD systems follows Part X at input/output ≤ 1000 V and Part XI above (SR-7544, 2021 cycle). Sections present: 430.120, 430.122, 430.124, 430.126, 430.128, 430.130, 430.131 — 430.129 (and 121/123/125/127) do not exist.

How are VFD supply conductors sized?

125% of the drive's RATED INPUT CURRENT (430.122(A)) — read the drive nameplate, not the motor FLC table. With a bypass device: larger of 125% input current and 125% motor FLC (430.122(C)). Several motors/other loads: 430.24 with the drive's input current (430.122(D), 2023). EX1: 20 A drive → 25.0 A → 12 AWG Cu.

What is "Suitable for Output Motor Conductor Protection" (SOOCP)?

A listing mark on the drive that (1) relaxes the output-conductor rule — 430.122(B) exception, larger of 125% motor FLC or the drive's marked minimum conductor — and (2) lets the branch OCPD be sized from the drive's rated INPUT current — 430.130(A) exception to (1). Neither appears anywhere in the 2017 code (verified); both are in the 2023 code, and the 2021-cycle SRs show they predate the 2023 cycle (introducing edition not pinnable from on-disk sources — disclosed).

Where does the disconnect go and how is it rated?

430.128 (both editions, word-identical): permitted in the incoming line to the conversion equipment, rating ≥ 115% of the drive's rated input current — not 115% of motor FLC (that's 430.110 for motor disconnects). EX4: 20 A drive → 23.0 A → 25 A.

What OCPD for a VFD branch circuit?

430.130(A)(1): Table 430.52(C)(1) — 300% nontime / 175% dual / 800% instantaneous / 250% inverse — on the motor FLC (430.6(A) or (B)); SOOCP drives may use the rated input current instead (2023 exception); the manufacturer's maximum stipulated rating always caps (A)(2); instantaneous-trip/semiconductor only integral to a listed assembly (A)(4); bypass circuits need their own protection (B). EX5/EX6.

What changed in Part X between NEC 2017 and 2023?

430.120 reword + the new 1000 V/Part XI sentence (SR-7544); 430.122 restructured (bypass rule (B)→(C) trimmed, new (B) output-conductor rule + SOOCP + two notes, new (D) via 430.24); 430.130(A) restructured ("all of the following", 430.6(A) or (B), new SOOCP exception + two notes, "motor controller"); 430.126(A)(3) drops "or (B)(2)" and 430.126(C) drops "The provisions of". Word-identical: 430.124, 430.128, 430.130(B), 430.131. All numbers unchanged; 430.129 absent in both editions; 2017 OCR corrections disclosed. 87 on-disk checks (verify_art44.py); 2020 scan ends at Article 230 so no 2017→2020 diff is claimed; SR-8024's "when"→"where" is a 2026-cycle change.