Akash Hirpara UL 1741-SB is Supplement B to UL 1741, the inverter listing standard published by Underwriters Laboratories. UL 1741-SB explicitly tests inverter compliance with IEEE 1547-2018 grid-support functions and is required for new solar installations in most US states.
Quick Facts
| Field | Detail |
|---|---|
| Term | UL 1741-SB — Inverter Listing, Supplement B |
| Category | US Solar Codes |
| Engineering Discipline | Inverter Certification |
| Published | 2020 (Supplement B) |
| Aligned With | IEEE 1547-2018 |
| Test Standard | IEEE 1547.1-2020 |
| Adopted by | CPUC Rule 21, NY SIR, Hawaii Rule 14H, and most state interconnections |
| Difficulty Level | Intermediate |
What is UL 1741-SB?
Formal definition
UL 1741, “Inverters, Converters, Controllers and Interconnection System Equipment for Use with Distributed Energy Resources,” Supplement B. Published by Underwriters Laboratories and CSA Group as a joint standard testing equipment for compliance with IEEE 1547-2018.
Engineering definition
UL 1741-SB defines test procedures for autonomous and dispatched grid-support functions: voltage and frequency ride-through curves, anti-islanding within 2 seconds, volt-VAR Q-V curves, volt-Watt P-V curves, frequency-Watt droop, and dynamic reactive power.
Industry definition
The current US inverter listing standard. Specifying a UL 1741 (without SB) inverter for new installations in California, New York, Hawaii, etc. results in interconnection rejection.
Permitting definition
Permit applications and interconnection applications reviewed by the AHJ both require evidence of UL 1741-SB listing — typically the inverter datasheet plus the UL Product iQ listing certificate.
How UL 1741-SB Differs from Earlier Versions
| Version | Year | Tests |
|---|---|---|
| UL 1741 (base) | 2010 | Anti-islanding, basic disconnection (IEEE 1547-2003) |
| UL 1741-SA | 2016 | + Grid-support functions per Rule 21 Phase 1/2 |
| UL 1741-SB | 2020 | + IEEE 1547-2018 + Phase 3 communications |
| UL 1741-CRD | Ongoing | Additional Certification Requirements Decisions |
Why UL 1741-SB Matters
Equipment compliance. The single requirement that gates new US solar interconnection.
Grid support. Inverters with UL 1741-SB actively support grid voltage and frequency.
Future-proofing. Adopting UL 1741-SB now avoids re-certification when more states phase in IEEE 1547-2018.
Permitting. Without UL 1741-SB, interconnection application denied.
Engineering Deep Dive
Functions tested by UL 1741-SB
- Voltage and frequency operating range (continuous, must-disconnect, must-trip).
- Voltage ride-through (Category I, II, III curves).
- Frequency ride-through.
- Volt-VAR (autonomous reactive power based on voltage).
- Volt-Watt (active power curtailment at high voltage).
- Frequency-Watt (overfrequency droop).
- Dynamic reactive power (fast reactive support).
- Specified power factor mode.
- IEEE 2030.5 SunSpec communications (Phase 3).
- Anti-islanding detection within 2 seconds.
Category I/II/III voltage ride-through
- Category I: minimal voltage support (legacy inverters).
- Category II: typical for residential/commercial.
- Category III: high-penetration zones; tighter ride-through requirements.
Permitting Implications
UL 1741-SB listing must be confirmed on the inverter datasheet and listed in the interconnection application. CPUC publishes a definitive California-approved inverter list, and the California AHJ solar permit guide walks through how that list is checked during local plan review.
Common Mistakes
- Specifying UL 1741-SA inverter when UL 1741-SB is required.
- Configuring inverter without enabling the smart inverter settings the utility requires.
- Disabling grid-support functions to maximize yield (illegal in most states).
- Missing IEEE 2030.5 communication infrastructure for Phase 3 commercial projects.
Best Practices
- Verify UL 1741-SB listing on the manufacturer datasheet before quoting.
- Check the utility’s approved inverter list (PG&E, SCE, SDG&E publish their own).
- Document smart inverter settings in the commissioning report.
- Maintain firmware updates that preserve UL 1741-SB compliance.
Standards & Certifications
- UL 1741 (base standard).
- UL 1741-SA (Supplement A, 2016).
- UL 1741-SB (Supplement B, 2020).
- IEEE 1547-2018 (technical requirements).
- IEEE 1547.1-2020 (conformance test procedures).
Related Reading
For EPCs preparing US inverter submittals, the Solar Permit Design FAQ answers the plan-review questions that come up most often around inverter listings, and How to Submit a Solar Permit Package to an AHJ shows where the UL 1741-SB certificate fits inside a complete submittal. Projects that mix scopes should also see Commercial vs. Residential Solar Permit Design, since Phase 3 IEEE 2030.5 communications requirements are enforced more strictly on commercial interconnections. Outside the US, where UL 1741-SB doesn’t apply, Solar Inverter Certification Standards compares it against IEC-based inverter frameworks, including IEC 62109, the safety standard most non-US markets test against instead.
Key Takeaways
- UL 1741-SB is the current US inverter listing standard, testing IEEE 1547-2018 compliance.
- Required by California Rule 21, New York SIR, Hawaii Rule 14H, and most states with high DER penetration.
- UL 1741-SA inverters are obsolete for new installations in most US jurisdictions.
- Major brands (Enphase, SolarEdge, SMA, Sungrow, Tesla, etc.) have UL 1741-SB listings; verify on the manufacturer datasheet.
- Always confirm the utility’s approved inverter list before specifying.
Frequently Asked Questions
10 commonly searched questions about UL 1741-SB.
What is UL 1741-SB?
What is the difference between UL 1741, UL 1741-SA, and UL 1741-SB?
Is UL 1741-SB mandatory?
How do I find UL 1741-SB-listed inverters?
Do all inverter brands have UL 1741-SB listings?
What is the CRD (Certification Requirements Decision)?
Can I retrofit an existing UL 1741 inverter to UL 1741-SB?
Does UL 1741-SB apply to microinverters?
What happens during a UL 1741-SB test?
Is UL 1741-SB required for India?
Need engineering-backed solar designs?
Heaven Designs delivers PE-stamped solar design packages, structural calculations, electrical engineering, and utility-compliant permit plans.
