Nirav Dhanani UL 1741 SA (Supplement A), published in 2016, is a test supplement to the UL 1741 inverter standard. It verified California Rule 21 Phase 1 and 2 smart inverter functions such as ride-through, volt-VAR and volt-watt. UL 1741 SB, published in 2021 for IEEE 1547-2018, has replaced it for most new interconnection applications.
What is UL 1741 SA?
UL 1741 SA is the 2016 supplement that tested inverters for California Rule 21 smart functions. This page is for solar designers and permit teams checking UL1741SA listings on inverter datasheets. For the base standard and inverter lists, see UL 1741.
What UL 1741-SA Tested
UL 1741-SA added a specific test matrix to the base UL 1741 inverter listing, built around California’s Rule 21 rollout. Phase 1 functions covered anti-islanding detection and voltage/frequency ride-through, the inverter’s ability to stay connected through minor grid disturbances instead of tripping offline.
Phase 2 functions added autonomous grid-support behavior: volt-VAR (adjusting reactive power output based on local voltage) and volt-Watt (curtailing active power output at high voltage). An inverter listed under UL 1741-SA had been lab-tested against both phases, which is what made it eligible for California interconnection at the time.
Why was UL 1741 SA replaced by UL 1741 SB?
IEEE 1547, the underlying technical standard both supplements test against, was revised to the 2018 edition, which introduced a third tier of requirements: utility-dispatched communications functions using the IEEE 2030.5 SunSpec protocol. UL 1741-SA’s test matrix stopped at Phase 2 and had no way to certify those communications capabilities, so UL published Supplement B in 2021 to close the gap.
From that point forward, new interconnection applications in Rule 21 territory and most other high-DER states have required UL 1741-SB rather than SA. Systems that were already interconnected under UL 1741-SA are typically grandfathered and don’t need to be re-certified, but any new equipment installed today should carry the SB listing.
Related Reading
Because UL 1741-SA only comes up in practice on legacy California interconnections, it’s worth pairing this entry with UL 1741-SB to see exactly which test requirements changed between the two supplements. Anyone specifying equipment for a current project should also check the California AHJ solar permit guide, which covers how Title 24 and NEC 2020 (CEC) requirements interact with the utility’s own interconnection checklist.
For teams comparing US inverter listing rules against international certification frameworks, Qbits Energy’s guide to solar inverter certification standards is a useful reference point outside the US market.
The current test basis is IEEE 1547 with IEEE 1547.1 procedures, as required under California Rule 21.
Disclosure: Qbits Energy is a Heaven Designs group company.
Frequently Asked Questions
4 commonly searched questions about UL 1741-SA.
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