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 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.
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).
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.
