1. Energy code VSD requirements
No US energy code sets a variable-speed threshold at 50 HP or by NEMA starter size. Current thresholds are lower. The requirements attach to new installation and, under each code's alteration provisions, to replacement of the driven equipment (fan, pump, air handler) under permit. Replacement of a starter or bucket alone is not an enumerated trigger in any of the codes below.
Scroll table left / right →Alteration provisions that attach these requirements at equipment replacement: ASHRAE 90.1-2019 section 6.1.1.3 (direct replacement equipment shall comply); IECC C503.4 (altered or replaced mechanical components shall comply with C403); Title 24 section 141.0(b)2 (altered components and newly installed equipment serving the alteration shall meet current requirements); Washington WAC 51-11C-50300. Adoption edition varies by state; see section 2.| Code | Section | Equipment | Requirement | Threshold |
|---|
| ASHRAE 90.1-2013, -2016, -2019 | 6.5.3.2.1 | Individual VAV supply fans | Mechanical or electrical VSD, or control producing max 30% design wattage at 50% flow | 7.5 HP |
| ASHRAE 90.1-2016, -2019 | Table 6.5.3.2.1 | CHW / evaporative AHU supply fans | Two-speed (max 66% speed, 40% power) or modulating control | 1/4 HP |
| ASHRAE 90.1 | 6.5.5.2.1 | Heat rejection fans | VSD or two-speed | 7.5 HP |
| ASHRAE 90.1 | 6.5.4.2 | Hydronic pumping systems with modulating valves | Variable flow, min 50% turndown | 10 HP system |
| IECC 2012, 2015 | C403.4.2 | Individual VAV fans | VSD or equivalent | 7.5 HP |
| IECC 2018, 2021 | C403.4.4 | Pumps operating continuously or on schedule | Variable speed drive | 2 HP |
| California Title 24 | 140.4(m) | AHU and fan-coil supply fans | Two-speed or VSD | 1/4 HP |
| Washington WSEC | WAC 51-11C-40344 (C403.4.4) | Scheduled or continuous pumps; Table C403.4.4 HW/CHW pumps | Variable speed drive | 2 HP; 7.5 HP per table |
| NYC Energy Code | Hydronic variable flow provisions | Chilled water pumps | Variable flow / VSD, max 30% wattage at 50% flow | 5 HP |
2. Where the requirements are in force: state adoption, August 2026
The provisions in section 1 apply only where a jurisdiction has adopted a code edition that contains them. The pump VFD rule (2 HP) requires an IECC 2018 or newer base, or ASHRAE 90.1-2019 equivalent. The VAV fan rule (7.5 HP) requires IECC 2012 or 90.1-2013 or newer.
Scroll table left / right →Compiled Aug 2026 from the ACEEE State Policy Database (commercial code table) cross-checked against primary state sources: NY DOS notice of adoption, PA Dept. of Labor and Industry, MI LARA final rules, TN State Fire Marshal, TX SECO, Ohio BBS compliance flowchart, WA SBCC. No mandatory statewide commercial code: Kansas, Missouri, North Dakota, South Dakota, Alaska (state facilities only). Very old editions with neither provision: Arkansas and South Carolina (IECC 2009), Oklahoma, Louisiana (90.1-2007; a 2024 update is reported but unverified). Adoption changes; verify with the authority having jurisdiction.| State | Commercial code in force | Base edition | Fan VSD (7.5 HP VAV) | Pump VFD (2 HP) |
|---|
| California | Title 24 Part 6, 2025 Energy Code | exceeds IECC 2021 | yes | yes |
| Washington | 2021 WSEC, effective Mar 2024 | exceeds IECC 2021 | yes | yes |
| Oregon | OEESC, effective Apr 2021 | ASHRAE 90.1-2019 | yes | yes |
| New York | 2025 ECCCNYS, effective Dec 31, 2025 | IECC 2024 / 90.1-2022 | yes | yes |
| Massachusetts | 10th edition base code plus stretch code | IECC 2021 | yes | yes |
| New Jersey | Adopted Sept 2022 | ASHRAE 90.1-2019 | yes | yes |
| Pennsylvania | UCC, IECC 2018; IECC 2021 effective Jan 1, 2026 | IECC 2018 to 2021 | yes | yes |
| Virginia | 2021 Virginia codes, effective Jan 2024 | IECC 2021 / 90.1-2019 | yes | yes |
| Florida | FBC Energy Conservation 8th ed., effective Dec 2023 | IECC 2021 / 90.1-2019 | yes | yes |
| Illinois | Illinois Energy Conservation Code, effective Jan 2024 | IECC 2021 | yes | yes |
| Ohio | 2024 OBC, comply via IECC 2021 or 90.1-2019 | IECC 2021 / 90.1-2019 | yes | yes |
| Michigan | 2021 Michigan Energy Code, effective Apr 2025 | ASHRAE 90.1-2019 | yes | yes |
| Minnesota | Effective Jan 2024 | ASHRAE 90.1-2019 | yes | yes |
| Tennessee | IECC 2021 commercial, effective Apr 2025 | IECC 2021 | yes | yes |
| Connecticut | 2022 State Building Code | IECC 2021 | yes | yes |
| Colorado | HB22-1362: IECC 2021 required at any local code update after Jul 2023 | IECC 2021 rolling | yes, where updated | yes, where updated |
| Texas | IECC as of May 1, 2015 statewide; Austin, Houston, Dallas on IECC 2021 | IECC 2015 | yes | no statewide; yes in IECC 2021 cities |
| Georgia | IECC 2015 with amendments, 90.1-2013 path | IECC 2015 | yes | no |
| North Carolina | 2018 NC ECC, effective Jan 2019 | IECC 2015 | yes | no |
| Wisconsin | SPS 363 | IECC 2015 / 90.1-2013 | yes | no |
| Indiana | 2010 Indiana Energy Conservation Code | ASHRAE 90.1-2007 | no | no |
| Arizona | No statewide code; Phoenix, Tucson, Chandler on IECC 2018 | IECC 2018, major cities | yes, cities | yes, cities |
Scroll table left / right →Sources: NYC DOB Energy Code Rules handbook and Buildings Bulletin 2026-005; Seattle SDCI; City of Chicago; Denver CPD; City of Austin; Mass.gov 225 CMR 22/23; Illinois CDB.| City / program | Code | Relation to state baseline |
|---|
| New York City | NYCECC; 2025 edition effective Dec 31, 2025, DOB enforcement from ~Mar 2026 | Required by Admin Code 28-1001.3.1 to meet or exceed the state code; DOB performs energy-code progress inspections |
| Seattle | 2021 Seattle Energy Code, amending the 2021 WSEC | Exceeds the most aggressive state code; fan speed control at C403.8.6.1, hydronic controls at C403.4; SDCI dedicated energy plan review |
| Chicago | 2022 Energy Transformation Code, permits from Nov 2022 | IECC 2021 base with amendments, ahead of prior Illinois baseline |
| Denver | 2022 Denver Energy Code | IECC 2021 plus amendments; Green Building Ordinance above 25,000 sq ft |
| Austin | Austin Energy Code, effective Sept 2021 | IECC 2021 in a state on IECC 2015 |
| Massachusetts stretch communities | Stretch code in ~272 of 351 municipalities; opt-in Specialized Code in 29+ | Exceeds the IECC 2021 base code |
| Illinois stretch | 2023 Commercial Stretch Code, IECC 2024 base, available from Jan 2025 | Supersedes the state code where a municipality adopts it |
Enforcement is weaker than adoption. The DOE/PNNL commercial field study (PNNL-32157, 230 buildings) found 4 of 230 fully code-compliant, with HVAC controls among the largest sources of lost savings. No published study measures enforcement of the alteration provisions at equipment replacement specifically. Jurisdictions with dedicated energy plan review (Seattle SDCI, NYC DOB progress inspections, Massachusetts stretch communities) demonstrably review these provisions at permit; elsewhere, like-for-like replacement work is frequently permitted without energy review.
3. Why a large motor cannot go back in as a starter bucket
Three documented constraints converge on motors of roughly 100 HP and up: the inrush a full-voltage start draws, the limits utilities place on that inrush, and the physical ceiling on what fits in an MCC unit.
Scroll table left / right →Locked-rotor values: NEMA MG 1, Section II Part 12, Table 12-1A (230 V values halved for 460 V per the table's own voltage rule); the same series appears in NEC Table 430.251(B). Ratio is about 6x FLC; Eaton's application literature states 6 to 8x for NEMA Design B (101 Basics Series, Module 21, Reduced Voltage Starters). Motors 15 HP and up carry locked-rotor kVA Code G, 5.6 to 6.3 kVA per HP.| Motor (460 V) | FLC (NEC 430.250) | Max locked-rotor current, Design B |
|---|
| 100 HP | 124 A | 725 A |
| 150 HP | 180 A | 1,085 A |
| 200 HP | 240 A | 1,450 A |
| 250 HP | 302 A | 1,825 A |
| 300 HP | 361 A | 2,200 A |
| 400 HP | 477 A | 2,900 A |
Scroll table left / right →Three verified examples spanning an investor-owned utility, a multi-state utility, and a rural cooperative. Voltage dip scales as starting kVA over source kVA times source reactance (NEMA MG 1 32.18.5.2, as published in Cummins bulletin 5544188); Kohler's generator sizing guide carries the same starting-kVA method.| Utility | Published limit | Document |
|---|
| PG&E (California) | Rule 2 Table 1 allows 711 A starting current at 460 V, a table that ends at 100 HP; larger motors require PG&E consultation and suitable starting equipment at customer expense. A Design B 100 HP motor may legally draw 725 A locked rotor, above the table ceiling. | PG&E Electric Rule No. 2, section F.4, Motor Starting Current Limitations |
| Xcel Energy | Starting kVA generally not to exceed 6x full-load kVA; flicker held to IEEE 1453 with a 4% maximum; remedies include 15+ second ramp rates; noncompliance can mean discontinuance of service. | Xcel Standard for Electric Installation and Use, sections 6.4.3 and 6.4.4 (2026) |
| Trico Electric Cooperative (AZ) | Reduced-voltage starting mandatory at 200 HP and above, and may be required from 40 HP. | Trico Electric Service Requirements Book 2025-7, section 1.15.2 |
Scroll table left / right →Sources: Rockwell 2100-SG003G-EN-P (July 2025) Bulletin 2162/2163 tables and drive placement rules; Eaton catalog CA08100004E Vol. 3 Tab 3; Siemens tiastar selection guide SIEA-C40019-00-4AUS. The engineering driver is heat: drive loss is approximately 3.5% of throughput power per the Siemens guide, so a 150 HP drive dissipates roughly 3.9 kW into one enclosed section, an order of magnitude more than the section's bus. This is why drive units sit at section bottoms, take wider structures, and stop at these ratings, and why larger drives go on the wall fed from a breaker feeder bucket.| Manufacturer | Drives available inside the MCC | Where it ends |
|---|
| Rockwell CENTERLINE 2100 | PowerFlex 753/755 units to 300 HP normal duty | A 100 HP drive unit is already a full 72" section 25" wide; 250-300 HP takes a 35" wide, 20" deep section. Nothing above 300 HP. All drive units are frame-mounted; plug-in stabs remain 225 A. |
| Eaton Freedom | SVX9000 plug-in units 3-30 HP only; frame-mounted to 700 HP | Everything 100 HP and up consumes a full section; 18-pulse versions take 40" to 106" wide dedicated structures; 250 HP and up unavailable in arc-resistant Freedom. |
| Siemens tiastar | SINAMICS G120 units to 150 HP | The 150 HP unit is a full 72" mounting height in a 20" x 20" structure. Nothing larger is cataloged. |
4. Feeder unit sizing, 460 V three-phase
Scroll table left / right →FLC values: NEC Table 430.250, three-phase induction, 460 V; 230 V values are double. Drive rated input: 94-100% of rated output for drives with DC link chokes (ABB ACH580, Danfoss FC series, PowerFlex 750 series; see section 4), 105-115% for chokeless drives (PowerFlex 525 frames A-D). Breaker column: 125% of FLC rounded up to the next standard rating between 15 and 400 A. The drive's marked maximum input protection governs where lower (NEC 430.130(A)(2)). Unit heights per the height rules in the bucket size reference.| Motor | FLC per NEC 430.250 | Typical drive rated input | Feeder breaker at 125% FLC | Unit height |
|---|
| 50 HP | 65 A | 61-65 A | 90 A | 12" |
| 60 HP | 77 A | 72-77 A | 100 A | 12" |
| 75 HP | 96 A | 90-96 A | 125 A | 18" |
| 100 HP | 124 A | 117-124 A | 175 A | 18" |
| 125 HP | 156 A | 147-156 A | 200 A | 18" |
| 150 HP | 180 A | 169-180 A | 225 A | 18" |
| 200 HP | 240 A | 226-240 A | 300 A | 24" |
| 250 HP | 302 A | 284-302 A | 400 A | 24" |
| 300 HP | 361 A | 339-361 A | over 400 A | quote |
5. NEC Article 430 Part X requirements
Sections 430.120 through 430.131 govern adjustable-speed drive systems. Section numbering is unchanged across the 2017, 2020, and 2023 editions.
Scroll table left / right →Text cross-verified against UpCodes-hosted NEC, EC&M NEC series (2020 and 2023 editions), and JADE Learning change analysis of 430.122. NFPA verbatim text is paywalled; section numbers and percentages agree across all three secondary sources.| Section | Requirement |
|---|
| 430.122(A) | Supply conductors to the drive: ampacity not less than 125% of the drive rated input current. The drive nameplate input current is the basis, not motor FLC. |
| 430.122(C) | With a bypass: supply conductors sized at 125% of the larger of drive rated input current or motor FLC per 430.6. Adding bypass to an existing installation without resizing the feeder violates this section. |
| 430.124(A) | No separate overload device required where the drive is marked as including motor overload protection. |
| 430.126 | Motor overtemperature protection required where the motor is not rated to operate at nameplate current over the drive speed range. |
| 430.128 | Disconnecting means permitted in the incoming line to the drive; rating not less than 115% of drive rated input current. An MCC feeder unit with through-the-door operator meeting 115% qualifies as the drive disconnecting means. |
| 430.130(A)(1) | Branch short-circuit and ground-fault protection per 430.52 using motor FLC from Table 430.250; drives listed and marked "Suitable for Output Motor Conductor Protection" may use drive rated input current instead. |
| 430.130(A)(2) | The drive manufacturer’s marked maximum branch protective device rating shall not be exceeded. |
6. Drive manual protection maxima, 480 V
Scroll table left / right →ABB: Technical Note 019, document 3AXD50000645015 Rev C. ABB permits only specific tested current-limiting breaker types at 460 V on the ACx580 family; non-current-limiting breakers are not permitted. Rockwell: publication 750-TD001, 480 V input protection tables; inverse-time breakers permitted to the listed maxima. Danfoss: FC 202 Design Guide MG22B202 Table 7.1, maximum external mains fuses.| Drive (normal duty) | HP | Rated input | Max fuse | Max breaker |
|---|
| ABB ACH580-01-124A-4 | 100 | 124 A | 200 A Class T or J | 225 A, tested current-limiting types only |
| ABB ACH580-01-180A-4 | 150 | 180 A | 300 A Class T or J | 250 A, tested current-limiting types only |
| ABB ACH580-01-240A-4 | 200 | 240 A | 350 A Class T or J | 400 A, tested current-limiting types only |
| PowerFlex 755 code D125 | 100 | 117.4 A | 175-275 A dual-element | 375 A inverse-time |
| PowerFlex 755 code D186 | 150 | 174.6 A | 250-400 A dual-element | 550 A inverse-time |
| PowerFlex 755 code D248 | 200 | 232.8 A | 325-550 A dual-element | 700 A inverse-time |
| Danfoss FC 202 N110K | 150 | 183 A | 315 A | per manual |
| Danfoss FC 202 N132 | 200 | 231 A | 350 A | per manual |
Manufacturer positions on breakers differ. Rockwell permits standard inverse-time breakers to the listed maxima. ABB requires Class T or J fuses, or breakers from its tested current-limiting list. Where the drive brand is not fixed at bucket ordering time, a breaker feeder sized per section 4 with provision for Class T or J fusing at the drive satisfies both.
7. Short-circuit current rating
Scroll table left / right →UL 61800-5-1 replaced UL 508C in February 2020. A drive's usable SCCR is conditional on the specific protective device installed ahead of it. Available fault current at the drive must not exceed the SCCR corresponding to the device actually installed in the feeder unit.| Item | Value | Source |
|---|
| Default SCCR, unspecified protection (UL 61800-5-1) | 5 kA | Schneider VFD SCCR application guide |
| ABB ACx580 with specified fuses | 100 kA at 240/480/600 V | ABB Technical Note 019 |
| ABB ACx580 with listed tested breakers | 65 kA | ABB Technical Note 019 |
| PowerFlex 525 label | 100 kA maximum; actual rating determined by AIC of installed protective device | Rockwell publication 520-UM001 |
8. Grounding and conduit
Scroll table left / right →| Requirement | Source |
|---|
| Drive ground leakage exceeds 3.5 mA: PE conductor minimum 8 AWG, or two separate ground conductors, each individually sized. | Danfoss FC 202 Design Guide MG22B202 |
| Insulated equipment grounding conductor to the drive PE terminal, in addition to conduit bonded at both ends. | ABB ACH580-01 Quick Installation Guide (UL/NEC) |
| Input and output conductors not in shared conduit. | ABB ACH580-01 Quick Installation Guide (UL/NEC) |
9. Example: 150 HP, 460 V, ABB ACH580-01-180A-4
Scroll table left / right →Resulting order specification: Square D Model 6 feeder unit, 18", 225 A, 65 kAIC breaker. A 30" Size 5 FVNR starter unit replaced by this feeder returns 12" of section space.| Step | Calculation | Result |
|---|
| Drive rated input | nameplate | 180 A |
| Supply conductors, 430.122(A) | 180 x 1.25 | 225 A min ampacity |
| Disconnect minimum, 430.128 | 180 x 1.15 | 207 A |
| Feeder breaker | next standard rating covering both | 225 A |
| ABB maximum protection | Tech Note 019 | 300 A Class T/J fuse or 250 A tested breaker; 225 A complies |
| Unit height, Square D Model 6 | 225 A breaker | 18" feeder unit |
| Fault duty | bucket breaker 65 kAIC; drive SCCR per installed protection | verify against available fault current |
Sources
1. NEC Article 430 Part X via UpCodes, EC&M NEC Motors series Part 10 and Part 2 of 2 (2023 ed.), JADE Learning analysis of 430.122.
2. ABB Technical Note 019, Branch Circuit Protection for ABB Drives, 3AXD50000645015 Rev C.
3. ABB Technical Note 023, UL 508C transition to UL 61800-5-1, LVD-EOTKN023U-EN.
4. ABB ACH580-01 Quick Installation and Start-up Guide (UL/NEC).
5. Rockwell publication 750-TD001, PowerFlex 750-Series Technical Data.
6. Rockwell publication 520-UM001, PowerFlex 520-Series User Manual.
7. Rockwell publication DRIVES-IN001, Wiring and Grounding Guidelines for PWM AC Drives.
8. Danfoss FC 202 Design Guide, MG22B202.
9. Schneider Electric, Variable Frequency Drives and Short-Circuit Current Ratings.
10. ASHRAE 90.1 (6.5.3.2.1, 6.5.4.2, 6.1.1.3); ASHRAE Interpretation IC-90.1-2013-4; IECC C403.4.2/C403.4.4/C503.4; California Title 24 sections 140.4(m), 141.0(b)2; WAC 51-11C-40344, 51-11C-50300.
11. ACEEE State Policy Database, commercial code table, cross-checked against state primary sources (NY DOS, PA L&I, MI LARA, TN SFMO, TX SECO, Ohio BBS, WA SBCC), Aug 2026.
12. PNNL-32157, Commercial Building Energy Code Field Study, DOE/PNNL.
13. NEMA MG 1, Section II Part 12, Tables 12-1A/12-1B; Eaton 101 Basics Series, Module 21.
14. PG&E Electric Rule No. 2 (F.4); Xcel Energy Standard for Electric Installation and Use (6.4.3, 6.4.4); Trico Electric Cooperative ESRB 2025-7 (1.15.2).
15. Cummins bulletin 5544188; Kohler, Sizing Generators for Motor Starting.
16. Rockwell 2100-SG003G-EN-P drive unit tables; Eaton CA08100004E Vol. 3 Tab 3; Siemens tiastar selection guide SIEA-C40019-00-4AUS.
Related: lineup identification, unit height by amperage, breaker interrupting ratings.
