Keyur Rakholiya UL 1741 SB (Supplement SB) is the certification route in the UL 1741 inverter standard that tests grid-support functions to IEEE 1547.1-2020 to show conformance with IEEE 1547-2018. Many US utilities now require SB-certified inverters for interconnection, and the certificate must come from a Nationally Recognized Testing Laboratory (NRTL) and cover the exact model and firmware.
UL 1741 SB is the inverter certification US utilities increasingly ask for in interconnection applications. This entry is for solar designers, installers and procurement teams who need to know what UL 1741 SB covers, how it relates to IEEE 1547-2018, and how to check a specific inverter.
Quick facts
| Field | Detail |
|---|---|
| Term | UL 1741 Supplement SB |
| Category | US solar codes |
| Equipment | Grid-interactive inverters, converters, controllers, and related DER equipment within the certificate scope |
| Requirements standard | IEEE 1547-2018 |
| Conformance test standard | IEEE 1547.1-2020 |
| Adoption | Jurisdiction and utility specific |
| Project check | Rule, exact model, firmware, and settings |
What is UL 1741 SB?
Formal definition
UL 1741 Supplement SB is part of the UL 1741 equipment standard. It connects the equipment certification process to IEEE 1547.1-2020 conformance testing for IEEE 1547-2018 requirements.
IREC reports that Supplement SB was introduced in August 2020. Further clarifications were published with the third edition of UL 1741 on September 28, 2021. Those public dates explain why a certificate should identify its edition and issue date.
Engineering definition
SB certification shows that a covered equipment configuration completed the applicable evaluation. Coverage can depend on the full model, electrical rating, voltage, control configuration, and firmware. The certificate or listing defines the boundary.
The certification does not select utility settings. It also does not decide whether the project falls under a particular state or utility rule.
Permitting definition
For a plan set or interconnection package, SB is one equipment record. The designer should also record the governing utility rule, exact scheduled model, covered firmware, and required settings.
How UL 1741 SB fits with IEEE 1547
The documents have different jobs:
| Document | Job |
|---|---|
| IEEE 1547-2018 | States DER interconnection and interoperability requirements |
| IEEE 1547.1-2020 | States conformance test procedures |
| UL 1741 Supplement SB | Supports product certification using that test route and UL clarifications |
| Utility tariff and source requirements | Establish local adoption, settings, and submission evidence |
The letters in Supplement SA and Supplement SB do not map to IEEE performance Categories A and B. Treat the supplement and performance category as separate fields.
UL 1741 SA vs SB
Supplement SA supported advanced-inverter testing before the national IEEE 1547-2018 conformance route was available. California and other early markets used SA-era procedures.
Supplement SB followed IEEE 1547.1-2020. It supports the certification route aligned with IEEE 1547-2018. Existing projects can still fall under transition rules, so an older SA record should be evaluated against the application date and utility requirements.
| Question | SA | SB |
|---|---|---|
| Advanced inverter test route | Earlier route | IEEE 1547.1-2020-based route |
| Performance category | Separate decision | Separate decision |
| Utility settings included | No | No |
| Local adoption still required | Yes | Yes |
How to verify a listed inverter
Confirm these fields before equipment release:
- Serving utility, application track, tariff revision, and effective date.
- Full manufacturer model, suffix, AC rating, nominal voltage, and phase.
- NRTL, certificate number, UL 1741 edition, and Supplement SB scope.
- Firmware, software, regional profile, and required control accessories.
- Utility-selected categories, operating modes, communications, and settings.
The California Energy Commission publishes a Grid Support Solar Inverter List. Its page warns that listed products can provide different levels of advanced functionality. It directs users to verify the required functionality with the utility, AHJ, or responsible entity.
Common mistakes
- Treating a base UL 1741 reference as proof of SB scope.
- Treating Supplement SB as IEEE performance Category B.
- Matching only the manufacturer instead of the full model and voltage.
- Omitting firmware or regional configuration from the record.
- Copying settings from another utility territory.
- Treating a California equipment list as nationwide approval.
- Assuming equal power ratings make two inverters interchangeable.
Related reading
For the project-level workflow, use the UL 1741 SB inverter verification guide. The IEEE 1547-2018 interconnection guide explains the requirements standard. The IEEE 1547.1 glossary entry covers the conformance test standard.
The solar interconnection application guide shows where the equipment record fits in a broader submission. California projects should also confirm the current Rule 21 tariff and serving utility materials.
Key takeaways
- UL 1741 SB is a certification route, not a utility settings profile.
- SB does not mean IEEE performance Category B.
- Adoption is jurisdiction specific, not universal across the United States.
- Certification is model and configuration specific.
- The utility rule, equipment record, firmware, and project settings must agree.
This glossary is a public-source summary. It does not reproduce paywalled UL or IEEE standard text. Project-specific decisions require review by the serving utility, AHJ, manufacturer, and responsible professional.
Frequently Asked Questions
4 commonly searched questions about UL 1741 SB.
What is the difference between UL 1741 SA and SB?
Is UL 1741 SB required everywhere in the United States?
How do I verify a UL 1741 SB certified inverter?
Does Supplement SB mean IEEE performance Category B?
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