In this guide
Short answer: UL 3700 is the first US safety standard written specifically for solar that plugs into an outlet. It checks the risks a normal inverter standard doesn't: live plug prongs, overloaded circuits, power flowing back during outages and safe DIY installation. Vermont requires it, New Jersey and Maine name it, and it's the safest thing to look for in any state.
Why a new standard was needed
Ordinary grid-tied solar is wired into your electrical panel by an electrician, behind its own breaker. Plug-in solar skips all that, which creates four new risks:
- The plug. A solar device pushes power out through a plug. If you pull it from the wall while the sun is shining, its prongs must not stay live.
- The circuit. Solar feeding an outlet adds to the current the wiring carries, while the breaker in the panel only sees what comes from the grid. This is called breaker masking.
- Outages. During a blackout, the device must stop feeding power to protect line workers and neighbors.
- The installer. The person setting it up is usually not an electrician, so the instructions, labels and construction must make safe use the easy path.
UL Solutions launched its certification program for UL 3700, the Outline of Investigation for Interactive Plug-In Photovoltaic Equipment and Systems, on January 8, 2026. It sets construction, performance and labeling criteria for these systems, including features that prevent accidental contact with live parts, overload protection, safe installation and protection against reverse power flow.
UL 3700 vs UL 1741
| UL 1741 | UL 3700 | |
|---|---|---|
| Written for | Inverters wired in by professionals | Systems plugged into an outlet |
| Plug and cord safety | Not covered | Covered |
| Circuit overload | Handled by the electrician's design | Must be handled by the device |
| Shuts off in outages | Yes (with IEEE 1547) | Yes |
| Labeling for consumers | Limited | Required |
| Accepted where | States with "UL or equivalent" wording | All states with a law |
A kit with a UL 1741 inverter isn't automatically unsafe, and Utah, Maryland and Connecticut accept general UL certification. But UL 3700 is the one standard that tests the whole plug-in situation, which is why newer laws name it.
Which states require what
- Vermont: UL 3700 is required, plus IEEE 1547-2018 default settings. See Vermont.
- New Jersey: UL 3700 for devices above 400 W, from March 1, 2027. See New Jersey.
- Maine: names UL 3700, also accepts comparable standards or NEC-compliant setups. See Maine.
- Colorado: devices above 391 W must be listed by a recognized lab. See Colorado.
- Utah, Maryland, Virginia, California, Connecticut: UL or an equivalent lab, without naming a standard.
Products announced so far
As of October 2026, these have been publicly announced or reported as certified to UL 3700. We haven't tested them.
- Hoymiles HiFlow Pro: microinverter announced in July 2026 as the first plug-in microinverter built to UL 3700.
- APsystems EZ1 (plug-in version): reported by Solar.com as CSA-certified to UL 3700 in July 2026; whole-kit certification was reported as pending in September.
- Mango Power: reported as the third company to certify, with a 1,200 W four-panel kit.
- EcoFlow STREAM Ultra and CraftStrom: certification reported as pending or applied for.
Details and prices are in our kit guide.
How to check a certificate in 3 minutes
- Find the lab and file number on the product label or spec sheet (UL, CSA, Intertek/ETL, TÜV and others are OSHA-recognized labs).
- Look it up in the lab's directory: UL Product iQ, the CSA certified product listing or Intertek's Directory of Building Products.
- Check the standard and the model: the listing should name UL 3700 and your exact model number, not a similar one.
- Check the scope: is the whole system certified, or only the inverter? Some state laws care about the system.
"Designed to UL 3700", "UL 3700 compliant" and "certification pending" are not certifications. Only a listing in the lab's directory is.
Frequently asked questions
What is UL 3700?
UL 3700 is UL Solutions' Outline of Investigation for Interactive Plug-In Photovoltaic Equipment and Systems. It sets construction, performance and labeling criteria for solar systems that plug into a household outlet. UL Solutions launched its certification program on January 8, 2026.
What is the difference between UL 3700 and UL 1741?
UL 1741 is the long-standing safety standard for grid-tied inverters wired in by an electrician. UL 3700 covers the extra risks of plugging into an outlet: live plug prongs, overloaded circuits, reverse power flow and installation by non-professionals.
Which states require UL 3700?
Vermont requires it. New Jersey requires it for devices above 400 W, and Maine names it while also allowing comparable standards. Utah, Maryland, Virginia, California and Connecticut require certification by UL or an equivalent lab without naming UL 3700.
Which plug-in solar products are UL 3700 certified?
As of October 2026, announcements include the Hoymiles HiFlow Pro microinverter (July 2026), the APsystems EZ1 plug-in version (reported as CSA-certified to UL 3700) and Mango Power's kit. Check the certificate yourself, because listings change and some products are only 'compliant' or 'pending'.
Can a lab other than UL certify to UL 3700?
Yes. Any nationally recognized testing laboratory accredited for the standard, such as CSA or Intertek, can test and certify to it. Vermont's law expressly accepts UL Solutions or an equivalent lab.
Update log
- Guide published. Product list checked against announcements up to October 2026.
Sources and official texts
- UL Solutions: UL Solutions debuts testing and certification framework for safer plug-in solar (Jan 8, 2026)
- Solar Builder: UL Solutions debuts testing criteria for plug-in solar systems
- pv magazine: How to design a UL-certified balcony solar kit in the United States (Feb 2, 2026)
- Vermont Legislature: Act 149 (S.202) as enacted
- OSHA: Nationally Recognized Testing Laboratory program