UL 3700, Explained
If you landed here from ul3700.com, this is the page you wanted. UL 3700 is the document that gives plug-in solar a safety certification path in the US for the first time — here's what it actually covers, and what it doesn't.
What it is
Published 11 December 2025 by UL LLC (the UL Solutions side of the business), UL 3700 is the "Outline of Investigation for Interactive Plug-In PV (PIPV) Equipment and Systems." The catalog listing is explicit: "UL LLC Outline of Investigation… © 2025 UL LLC."
It is an Outline of Investigation, not a finalized UL Standard. That's a pre-standard document used to certify products while the full standard is still being developed. Anyone telling you the US has a finished plug-in solar standard is overstating it — Germany's DIN VDE V 0126-95, published the same month after eight years of work, is a full standard. The US is earlier in the process than the headlines suggest.
What it's meant to prevent
Plug-in solar creates problems ordinary rooftop solar doesn't, because you're pushing power backwards into wiring designed only ever to deliver it. UL's own launch announcement gives four aims for the outline, in its wording:
- "Mitigate accidental contact with hazardous electric parts." An unplugged inverter still has panels feeding it, so accessible plug blades must not be live.
- "Promote safe installation." The whole premise is gear installed by whoever buys it, with no electrician in the loop.
- "Protect against overloads." Grid power plus solar power on one branch circuit can exceed what the wiring in your wall is rated for.
- "Prevent electric current from flowing in the wrong direction." Back-fed current can blind or damage the ground-fault protection already in your home — the thing meant to stop you being electrocuted. UL 3700's reference list includes UL 943, the ground-fault standard.
Most coverage compresses this into "three hazards." It's a fair summary, but it isn't UL's split. And an honest caveat: we've read the catalog listing and its reference list, not the full text. What the outline demands, as opposed to what it references, isn't something we can tell you from source yet — so we don't.
Technical scope
UL 3700 covers PV modules and DC circuits up to 64 VDC open-circuit (80 VDC once the 1.25 cold-temperature factor is applied). Systems above that are outside its scope.
Note this is a voltage limit, not a power cap. Germany's regime works differently — it caps AC output at 800W with up to 2,000W of modules. The two systems are not equivalent and there is no reciprocity: a unit certified for German Steckersolar carries no UL 3700 status, and vice versa.
"UL Certified" is not "UL 3700 Certified"
This is the distinction worth understanding before you spend money. Almost every electrical product sold in the US carries some UL mark. That says nothing about whether it's been evaluated as a plug-in PV system against the hazards above.
A microinverter can be legitimately UL-certified to a different standard and still be untested for back-feeding your house wiring. Treat a vague "UL Listed" claim on a plug-in kit as telling you nothing relevant, and look for the specific 3700 designation.
With one catch worth being blunt about: no kit on sale in the US carries it today. So this isn't yet a test you can apply at checkout — it's what to wait for, and what to hold a seller to when they start claiming it.
UL 3700 is one of several UL standards behind a plug-in system — the inverter, panels, battery, and racking each carry their own. See the whole UL certification stack →
Who's behind it
Two different organizations, constantly confused — including by us until we checked the catalog listing itself:
- UL Standards & Engagement (ULSE) — the nonprofit that writes consensus standards and runs the store this is sold through.
- UL LLC / UL Solutions — the for-profit that tests and certifies products, owns the UL Mark, and publishes Outlines of Investigation like UL 3700.
This isn't pedantry. An Outline of Investigation is a UL LLC certification instrument used where no consensus standard exists. A UL Solutions spokesperson confirmed to pv magazine USA in January 2026 that ULSE has not developed a consensus standard for plug-in solar. UL Solutions certifies to the outline — which is a weaker claim than "the US has a plug-in solar standard," and most coverage blurs the two.
BalconySolarHQ is independent of both.
Canada: not yet
A binational version, ANSI/CAN/UL 3700, is under development but unpublished. Until it lands there's no Canadian standard for plug-in PV — which means no certification path, which effectively keeps compliant plug-in solar out of Canada entirely. Ontario's ESA has issued a flash notice on PIPV. The cUL mark doesn't bridge this: it signals compliance with Canadian requirements, and for plug-in PV there aren't any yet.