Rule 21 is a California interconnection tariff, and it binds only the state’s investor-owned utilities: PG&E, SCE, SDG&E, Bear Valley Electric Service, Liberty Utilities (CalPeco) and PacifiCorp. If your project sits in SMUD, LADWP, Imperial Irrigation District or any other publicly owned utility territory, Rule 21 does not apply. That utility runs its own interconnection process, and filing a Rule 21 application there is a wasted step.
Key takeaways
- Scope first. Rule 21 is a CPUC-jurisdictional tariff covering six investor-owned utilities. It does not reach SMUD, LADWP, Imperial Irrigation District or any other publicly owned utility, nor projects selling into wholesale FERC markets.
- UL 1741 SB is what the IOUs require now. PG&E has required UL 1741 SB inverters plus Common Smart Inverter Profile conformance since 29 August 2023, and SCE requires SB under Section Hh of its Rule 21 tariff.
- SA is not banned, it is just not what the IOUs accept. The California Energy Commission’s lists carry inverters at different levels of advanced functionality, so CEC listing alone is not proof of compliance.
- All three phases have real dates. Phase 1 landed 8 September 2017, Phase 2 communications 22 March 2020, Phase 3 in pieces from 22 February 2019. Only Functions 4 and 7 are undated.
- It shows up on the drawings in four places: the equipment schedule, the certification note, the point of interconnection, and the utility disconnect callout.
- Avila Solar Drafting does not take projects in four jurisdictions, including Los Angeles County. The full list is APS and SRP territory in Arizona, the City of Peoria, AZ, the City of Phoenix, AZ, and Los Angeles County (LABD), CA; much of LA County, including the City of Los Angeles, is served by LADWP, which sits outside Rule 21 entirely.
What is Rule 21, and which utilities does it actually bind?
The California Public Utilities Commission defines Rule 21 as “a tariff that describes the interconnection, operating and metering requirements for generation facilities to be connected to an investor-owned utility’s (IOUs) distribution system and transmission system over which the California Public Utilities Commission (Commission) has jurisdiction.” That sentence settles the scope question, and most write-ups skip it. It is the first thing we pin down before drawing any of the California solar plan sets that come through our intake: which utility, and therefore which rulebook.
Rule 21 is not state law and not a building code. It is a tariff, filed by each utility and approved by the CPUC, and it reaches exactly as far as CPUC jurisdiction reaches. The CPUC’s Rule 21 page names those utilities: the large IOUs PG&E, SCE and SDG&E, plus the three small and multi-jurisdictional utilities, Bear Valley Electric Service, Liberty Utilities (CalPeco Electric) and PacifiCorp doing business as Pacific Power. Six utilities. That is the list. The same page carves out the other direction too: Rule 21 does not govern facilities headed for wholesale markets overseen by the Federal Energy Regulatory Commission.
| Utility type | Examples | Interconnection governed by | Smart-inverter standard to note on the drawings |
|---|---|---|---|
| Investor-owned utility (CPUC-jurisdictional) | PG&E, SCE, SDG&E, Bear Valley Electric Service, Liberty Utilities (CalPeco), PacifiCorp / Pacific Power | That utility’s Electric Rule 21, Section Hh | UL 1741 Supplement SB, per the utility’s own Rule 21 requirements |
| Publicly owned / municipal utility | SMUD, LADWP, Imperial Irrigation District, Roseville Electric | That utility’s own rules. It is outside CPUC jurisdiction, so Rule 21 does not reach it | Whatever that utility publishes. Confirm before drawing |
| Wholesale / FERC market participant | Projects selling into CAISO markets | FERC-jurisdictional interconnection process | Not set by Rule 21 |
What if the project is in SMUD, LADWP or another municipal territory?
Then Rule 21 is the wrong document and the CPUC is the wrong regulator. The CPUC’s own primer is blunt about the boundary: the Commission regulates investor-owned electric and natural gas utilities. The California Energy Commission’s register of load-serving entities keeps the categories separate for the same reason, listing PG&E, SCE, SDG&E, Liberty, PacifiCorp and Bear Valley as IOUs, and LADWP, SMUD, Imperial Irrigation District and Roseville Electric among the publicly owned utilities.
Practically, a municipal utility publishes its own interconnection agreement, application, equipment requirements and inverter settings. Some track Rule 21 closely. Some do not. Either way, drawings citing “Rule 21” on the cover sheet of a SMUD job cite a tariff that does not apply. This is one of the quieter reasons why permits get rejected: the set is technically fine but pointed at the wrong authority.
One boundary to state plainly: Avila Solar does not accept projects in four jurisdictions — APS and SRP territory in Arizona, the City of Peoria, AZ, the City of Phoenix, AZ, and Los Angeles County (LABD), CA. Much of LA County, including the City of Los Angeles, is served by LADWP, a publicly owned utility outside Rule 21 anyway. If your project is in LA County we are not the right drafting partner, and we would rather say so here than after you have filled in an intake form.
UL 1741 SA or UL 1741 SB: which does my inverter need?
For a new Rule 21 interconnection with a large IOU, the answer is UL 1741 Supplement SB. PG&E states it directly on its interconnections and renewables page: “PG&E will require interconnection applicants to use UL1741 SB Certified inverters and Common Smart Inverter Profile Conformance (CSIP) starting on August 29, 2023.” SCE’s Rule 21 page carries the matching requirement, that “Rule 21 applicants are required to use inverters that comply with UL 1741 SB requirements as specified in Section Hh of SCE’s Rule 21 tariff,” plus an attestation for the Phase 2 communication requirements established in Resolution E-5000.
What UL 1741 SB is matters for how you write the note. It is a supplement to the UL 1741 safety standard, and the test method used to show that grid-support inverters comply with IEEE 1547-2018, together with its test standard IEEE 1547.1-2020. So UL 1741 SB is the listing, IEEE 1547-2018 is the performance requirement behind it, and IEEE 2030.5 with the Common Smart Inverter Profile is the communications layer on top. Three separate things, frequently collapsed into one on a drawing note.
Now the error in the other direction. UL 1741 SA has not been outlawed. Neither the CPUC nor the California Energy Commission has published a hard sunset making SA-listed hardware illegal, and SA listings still exist. What changed is what the IOUs accept on a new smart-inverter interconnection. The accurate framing is “SB is what the IOU requires,” not “SA is banned.”
Appearing on a CEC list is necessary but not sufficient. The Grid Support Solar Inverters list notes that inverters on it are capable of different levels of advanced functionality. Listing is downstream of UL certification, not an alternative to it. PG&E recommends installers use CEC-listed equipment because unlisted equipment triggers extra documentation and slows engineering review.
Where did the three Rule 21 smart-inverter phases actually land?
All three phases have adopted dates, and all are in the past. The CPUC’s Smart Inverter Working Group publishes the schedule, and every requirement below sits in Section Hh of Electric Tariff Rule 21. Phase 1 covered the seven autonomous functions adopted in CPUC Decision 14-12-035, the ones an inverter performs without talking to anybody. Phase 2 set the default communication protocols between IOUs, distributed energy resources and DER aggregators, built on IEEE 2030.5 and the Common Smart Inverter Profile, required by 22 March 2020, not 2018. Phase 3 covers advanced functions that may or may not require communications, and it did not arrive as a single event.
| Phase | What it requires | Capability required by |
|---|---|---|
| Phase 1: autonomous functions | The seven autonomous smart-inverter functions adopted in CPUC Decision 14-12-035 | 8 September 2017 |
| Phase 2: default communications | Default communication protocols between IOUs, DERs and aggregators, based on IEEE 2030.5 and the Common Smart Inverter Profile | 22 March 2020 |
| Phase 3, Functions 5 and 6 | Frequency-Watt Mode and Volt-Watt Mode | 22 February 2019 |
| Phase 3, Functions 1, 2, 3 and 8 | Monitor Key DER Data; DER Cease to Energize and Return to Service Command; Limit Maximum Active Power Mode; Scheduling Power Values and Modes | 22 March 2020 |
| Phase 3, Functions 4 and 7 | Set Active Power Mode; Dynamic Reactive Current Support Mode | Still to be determined. No date adopted |
The takeaway for a designer: there is nothing left to wait for. Six of Phase 3’s eight functions have been required capability for years, and the two that remain have no adopted date. A currently listed UL 1741 SB inverter already carries what it needs.
What does Rule 21 actually change on the plan set?
Rule 21 is a utility document, but it lands on your drawings in specific, checkable places, alongside everything else in what a plan set includes.
- Cover sheet and general notes. Name the interconnecting utility and the tariff you are drawing to. For an IOU project that is the utility’s Electric Rule 21, Section Hh. Do not put “Rule 21” on a municipal job.
- Equipment schedule. Match the inverter manufacturer and model string to the CEC Grid Support Solar Inverters entry character for character. PG&E’s portal populates from CEC- and utility-approved equipment, and anything unlisted needs extra documentation.
- Certification note. State the listing explicitly: inverter listed to UL 1741 including Supplement SB, certified to IEEE 1547-2018 and IEEE 1547.1-2020, with IEEE 2030.5 CSIP conformance. A note reading only “UL listed” tells a reviewer nothing.
- Point of interconnection. Show whether you are landing supply side under NEC 2023 705.11 or load side under NEC 2023 705.12, and if load side, put the busbar calculation on the sheet. SCE requires a single-line drawing with the application, so the sheet you draw is the sheet the utility reads.
- Utility AC disconnect. Call out the device, its rating, its location relative to the meter, and the accessibility and lockability the utility asks for. Requirements differ across the IOUs.
- Site or plot plan. SCE asks for a site/plot plan drawing alongside the single-line. If the utility and building submittals pull from the same set, the site plan has to serve both.
- Export status and nameplate. Aggregate AC output and whether the system exports drives which Rule 21 path the application follows. Non-export projects carry extra documentation on the switching scheme, so the drawings must describe the limiting method, not just assert it.
Consistency is what saves time. If the equipment schedule, the single-line and the application name three slightly different inverter models, you will hear about it from both the utility and the building department. It is the failure mode behind most of the design success factors that separate a set that clears review from one that does not.
What still comes from the NEC and the AHJ, not from Rule 21?
Rule 21 gets blamed for things it never said. It is an interconnection tariff: it does not review your rafters, conductor sizing or labelling. Two reviewers read the same set for different reasons, and the drawings have to satisfy both.
The building department reviews against the California Electrical Code, Title 24 Part 3, whose 2025 edition took effect 1 January 2026 and is based on NFPA 70, the 2023 National Electrical Code, plus local amendments. That is where rapid shutdown under NEC 2023 690.12 lives, along with PV system disconnecting means under NEC 2023 690.13 and the power source identification directory under NEC 2023 705.10. Conductor ampacity, temperature-corrected string sizing, fire setbacks and structural attachment are AHJ territory, not utility territory, as we cover in our breakdown of NEC and storage requirements.
Local practice varies more than the code text suggests, which is the subject of permitting nuances. Structural or electrical scope may also need a licensed engineer’s seal, a separate decision from anything Rule 21 requires. If you are unsure when a PE stamp applies, make that call before the set goes out. We handle California engineering stamps when a project needs them.
How Avila handles California plan sets
Our intake asks for the interconnecting utility by name, because that single field determines which tariff the cover sheet cites and which disconnect detail goes on the electrical sheet. From there our solar drafting services produce a permit-ready set drawn to the code edition your jurisdiction has adopted and the rules of the utility you named.
Standard turnaround is 2-3 business days. Fast Roof sets come back in 1-2 business days. Pricing depends on scope and complexity — current figures are on the solar plan sets page, and a separate development and consultancy fee applies where the work is for a homeowner rather than a business. We draw the set. The authority having jurisdiction issues the permit and the utility approves the interconnection, so we make no promises about either outcome. And to repeat the exclusions: no projects in APS or SRP territory in Arizona, the City of Peoria, AZ, the City of Phoenix, AZ, or Los Angeles County (LABD), CA.
FAQ
Does Rule 21 apply if my project is in LADWP or SMUD territory?
No. Rule 21 is a CPUC-jurisdictional tariff, and the CPUC regulates investor-owned utilities. LADWP and SMUD are publicly owned, so they sit outside that jurisdiction and run their own interconnection processes, applications and equipment requirements. Citing Rule 21 on drawings for a municipal job gets you nowhere. Confirm the utility first.
Is a UL 1741 SA inverter still allowed in California?
SA-listed equipment has not been outlawed, and neither the CPUC nor the California Energy Commission has published a hard sunset. But Pacific Gas and Electric has required UL 1741 SB inverters and CSIP conformance since 29 August 2023, and Southern California Edison requires SB under Section Hh of its Rule 21 tariff. Write the note as what the utility requires, not as SA being prohibited.
Which Rule 21 smart-inverter phases are in effect right now?
All of Phase 1 and Phase 2, and six of the eight Phase 3 functions. Phase 1 was required by 8 September 2017, Phase 2 communications by 22 March 2020, Phase 3 Functions 5 and 6 by 22 February 2019, and Functions 1, 2, 3 and 8 by 22 March 2020. Only Functions 4 and 7 have no adopted date.
What has to appear on the plan set for a Rule 21 interconnection?
Name the utility and its Electric Rule 21, Section Hh on the cover sheet. Match the inverter make and model to the California Energy Commission Grid Support Solar Inverters list exactly. Add a certification note citing UL 1741 Supplement SB, IEEE 1547-2018, IEEE 1547.1-2020 and IEEE 2030.5 CSIP conformance. Show the point of interconnection per NEC 2023 705.11 or NEC 2023 705.12, call out the utility AC disconnect, and include a site plan.
Does Avila draw plan sets for California projects?
Yes, with exclusions: Avila does not accept projects in Los Angeles County (LABD), CA, or in three other jurisdictions — APS and SRP territory in Arizona, the City of Peoria, AZ, and the City of Phoenix, AZ. Everywhere else in California we produce permit-ready plan sets in 2-3 business days standard, or 1-2 business days for Fast Roof. Pricing depends on scope and complexity — current figures are on the solar plan sets page, with a separate development and consultancy fee where the work is for a homeowner rather than a business.
Settle the utility question before you draw
Most Rule 21 trouble is not a code problem. It is a set drawn to the wrong authority, or an inverter note that says less than the reviewer needs. Name the interconnecting utility on the intake form and we handle the rest.
Order online and we come back with questions rather than guessing. If you would rather talk through a tricky interconnection first, call us.
Or call 971-410-0655.
