Key takeaways
- UL 3700 was published by UL Solutions in December 2025; certification began on January 8, 2026.
- It tests the risks unique to plug-in systems: live plug prongs, anti-islanding, circuit overload and GFCI compatibility.
- UL 1741 certifies grid-tied inverters in general; UL 3700 certifies the plug-in system as a whole.
- Hoymiles' HiFlow Pro became the first UL 3700-certified microinverter in July 2026; APsystems' EZ1 followed.
- Most state laws require UL or equivalent certification — UL 3700 is the clearest way to meet that bar.
Every state plug-in solar law says some version of the same thing: the equipment must be certified by UL or an equivalent testing laboratory. Until recently there was no US standard written specifically for a solar system that plugs into a wall outlet. UL 3700 changes that.
What UL 3700 is
UL 3700 is a safety standard published by UL Solutions in December 2025 for plug-in photovoltaic systems — the small "balcony" kits that connect to a home through an ordinary receptacle. UL Solutions began certifying products against it on January 8, 2026.
It's the first American standard to treat the plug-in system as a whole, rather than certifying the panels and the inverter separately and leaving the connection to the home as an open question.
The risks it addresses
Plugging a generator into a wall outlet creates hazards that a conventional, hard-wired rooftop system doesn't:
1. Live plug prongs
If a solar plug is pulled from the wall while the panels are producing, could its metal prongs carry voltage? With a properly designed microinverter, no — it should stop exporting instantly when it loses the grid connection. UL 3700 tests this "dead-prong" behavior directly. This is why you must never use a homemade "suicide cable" with male prongs on both ends.
2. Islanding
When the grid goes down, a solar system that kept feeding power into the neighborhood lines could electrocute a line worker. Grid-tied inverters must detect the outage and shut down within a fraction of a second. UL 3700 verifies this anti-islanding function in the plug-in configuration.
3. Overloading the circuit
Your circuit breaker protects the wiring by measuring current coming from the panel. Solar current enters from the outlet. If a 15-amp circuit has a 1,200 W solar input and 1,800 W of appliances running, the wire between the two can carry more than the breaker ever sees. UL 3700 includes requirements for output limits and overcurrent protection; state laws add a hard cap, usually 1,200 W. See the 1,200-watt limit explained.
4. GFCI compatibility
Ground-fault circuit interrupters (GFCIs) — the outlets with test and reset buttons required outdoors and in kitchens and bathrooms — weren't designed for current flowing backward. UL 3700 addresses how plug-in systems interact with GFCI protection so that a ground fault still trips reliably.
5. Outdoor durability
Plug-in systems live outdoors, often on balconies exposed to rain, wind and UV. The standard includes environmental and weatherproofing requirements for the system.
UL 3700 vs. UL 1741
| UL 1741 (incl. SB) | UL 3700 | |
|---|---|---|
| Covers | Inverters and grid-interactive equipment | Complete plug-in PV systems |
| Anti-islanding | Yes | Yes, in plug-in configuration |
| Dead-prong protection | Not specifically | Yes |
| Branch-circuit overload | Not specifically | Yes |
| GFCI interaction | Not specifically | Yes |
| Typical use | Rooftop and commercial solar | Balcony / plug-in kits |
Many plug-in kits on the market in 2026 use microinverters certified to UL 1741-SB. That's a meaningful safety credential — it confirms anti-islanding and grid-support behavior — but it doesn't test the plug-in-specific risks above.
Which products are certified?
UL 3700 listings were scarce for most of 2026:
- Hoymiles HiFlow Pro became the first microinverter certified to UL 3700, in July 2026.
- APsystems EZ1 plug-in microinverter followed, certified by CSA to the UL 3700 standard.
More listings are expected through 2027 as manufacturers prepare for the California and New Jersey markets. Certification status changes quickly, so always verify a specific model before you buy.
How to verify a certification
- Find the certification mark on the product label or spec sheet — UL, CSA, Intertek (ETL) and TÜV are all nationally recognized testing laboratories that can certify to UL standards.
- Note the exact model number.
- Search the certifying lab's public database — for UL, the Product iQ database.
- Make sure the listing names UL 3700 (or, at minimum, UL 1741-SB for the microinverter) and matches your model.
Be wary of listings that say only "UL compliant," "meets UL standards" or "UL-recognized components." Those aren't the same as a certified, listed product.
Do you need UL 3700 today?
- Legally: most laws require "UL or equivalent" certification without naming a standard. Your utility or state regulator may issue guidance; check your state page.
- Practically: if a UL 3700-listed system is available at a reasonable price, buy it. It's the only certification that tests the exact way you'll use the product.
- At minimum: never buy a kit whose microinverter isn't certified to UL 1741 by a recognized lab.
Certified equipment is the single most important safety decision you'll make. Read our kit-buying guide next.
Frequently asked questions
Is UL 3700 required by law?
State laws generally require plug-in systems to be certified by UL or an equivalent nationally recognized testing laboratory, without naming a specific standard. UL 3700 is the standard designed for exactly this use, so a UL 3700 listing is the clearest evidence of compliance. Check your state's law and your utility's guidance.
What's the difference between UL 1741 and UL 3700?
UL 1741 (including its SB supplement) is the established standard for inverters that connect to the grid, covering grid-support functions such as anti-islanding. UL 3700 addresses the hazards specific to plugging a generator into a household receptacle: energized plug prongs, overloading of branch-circuit wiring and interaction with GFCI outlets.
Can I use a microinverter that's only UL 1741 certified?
Many plug-in kits sold in 2026 use UL 1741-SB microinverters, which provide anti-islanding protection. Whether that satisfies your state's certification requirement depends on the law and your utility's interpretation. Where available, a UL 3700-listed system is the safer choice.
How do I verify a UL certification?
Look for the certification mark on the product label, then confirm the listing in UL Solutions' Product iQ database (or the database of the certifying lab, such as CSA or Intertek) using the manufacturer name and model number.